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Diffstat (limited to 'third_party/git/Documentation/technical')
42 files changed, 1625 insertions, 2902 deletions
diff --git a/third_party/git/Documentation/technical/api-allocation-growing.txt b/third_party/git/Documentation/technical/api-allocation-growing.txt deleted file mode 100644 index 5a59b548448f..000000000000 --- a/third_party/git/Documentation/technical/api-allocation-growing.txt +++ /dev/null @@ -1,39 +0,0 @@ -allocation growing API -====================== - -Dynamically growing an array using realloc() is error prone and boring. - -Define your array with: - -* a pointer (`item`) that points at the array, initialized to `NULL` - (although please name the variable based on its contents, not on its - type); - -* an integer variable (`alloc`) that keeps track of how big the current - allocation is, initialized to `0`; - -* another integer variable (`nr`) to keep track of how many elements the - array currently has, initialized to `0`. - -Then before adding `n`th element to the item, call `ALLOC_GROW(item, n, -alloc)`. This ensures that the array can hold at least `n` elements by -calling `realloc(3)` and adjusting `alloc` variable. - ------------- -sometype *item; -size_t nr; -size_t alloc - -for (i = 0; i < nr; i++) - if (we like item[i] already) - return; - -/* we did not like any existing one, so add one */ -ALLOC_GROW(item, nr + 1, alloc); -item[nr++] = value you like; ------------- - -You are responsible for updating the `nr` variable. - -If you need to specify the number of elements to allocate explicitly -then use the macro `REALLOC_ARRAY(item, alloc)` instead of `ALLOC_GROW`. diff --git a/third_party/git/Documentation/technical/api-argv-array.txt b/third_party/git/Documentation/technical/api-argv-array.txt deleted file mode 100644 index 870c8edbfb1d..000000000000 --- a/third_party/git/Documentation/technical/api-argv-array.txt +++ /dev/null @@ -1,65 +0,0 @@ -argv-array API -============== - -The argv-array API allows one to dynamically build and store -NULL-terminated lists. An argv-array maintains the invariant that the -`argv` member always points to a non-NULL array, and that the array is -always NULL-terminated at the element pointed to by `argv[argc]`. This -makes the result suitable for passing to functions expecting to receive -argv from main(), or the link:api-run-command.html[run-command API]. - -The string-list API (documented in string-list.h) is similar, but cannot be -used for these purposes; instead of storing a straight string pointer, -it contains an item structure with a `util` field that is not compatible -with the traditional argv interface. - -Each `argv_array` manages its own memory. Any strings pushed into the -array are duplicated, and all memory is freed by argv_array_clear(). - -Data Structures ---------------- - -`struct argv_array`:: - - A single array. This should be initialized by assignment from - `ARGV_ARRAY_INIT`, or by calling `argv_array_init`. The `argv` - member contains the actual array; the `argc` member contains the - number of elements in the array, not including the terminating - NULL. - -Functions ---------- - -`argv_array_init`:: - Initialize an array. This is no different than assigning from - `ARGV_ARRAY_INIT`. - -`argv_array_push`:: - Push a copy of a string onto the end of the array. - -`argv_array_pushl`:: - Push a list of strings onto the end of the array. The arguments - should be a list of `const char *` strings, terminated by a NULL - argument. - -`argv_array_pushf`:: - Format a string and push it onto the end of the array. This is a - convenience wrapper combining `strbuf_addf` and `argv_array_push`. - -`argv_array_pushv`:: - Push a null-terminated array of strings onto the end of the array. - -`argv_array_pop`:: - Remove the final element from the array. If there are no - elements in the array, do nothing. - -`argv_array_clear`:: - Free all memory associated with the array and return it to the - initial, empty state. - -`argv_array_detach`:: - Disconnect the `argv` member from the `argv_array` struct and - return it. The caller is responsible for freeing the memory used - by the array, and by the strings it references. After detaching, - the `argv_array` is in a reinitialized state and can be pushed - into again. diff --git a/third_party/git/Documentation/technical/api-config.txt b/third_party/git/Documentation/technical/api-config.txt deleted file mode 100644 index 7d20716c32a4..000000000000 --- a/third_party/git/Documentation/technical/api-config.txt +++ /dev/null @@ -1,319 +0,0 @@ -config API -========== - -The config API gives callers a way to access Git configuration files -(and files which have the same syntax). See linkgit:git-config[1] for a -discussion of the config file syntax. - -General Usage -------------- - -Config files are parsed linearly, and each variable found is passed to a -caller-provided callback function. The callback function is responsible -for any actions to be taken on the config option, and is free to ignore -some options. It is not uncommon for the configuration to be parsed -several times during the run of a Git program, with different callbacks -picking out different variables useful to themselves. - -A config callback function takes three parameters: - -- the name of the parsed variable. This is in canonical "flat" form: the - section, subsection, and variable segments will be separated by dots, - and the section and variable segments will be all lowercase. E.g., - `core.ignorecase`, `diff.SomeType.textconv`. - -- the value of the found variable, as a string. If the variable had no - value specified, the value will be NULL (typically this means it - should be interpreted as boolean true). - -- a void pointer passed in by the caller of the config API; this can - contain callback-specific data - -A config callback should return 0 for success, or -1 if the variable -could not be parsed properly. - -Basic Config Querying ---------------------- - -Most programs will simply want to look up variables in all config files -that Git knows about, using the normal precedence rules. To do this, -call `git_config` with a callback function and void data pointer. - -`git_config` will read all config sources in order of increasing -priority. Thus a callback should typically overwrite previously-seen -entries with new ones (e.g., if both the user-wide `~/.gitconfig` and -repo-specific `.git/config` contain `color.ui`, the config machinery -will first feed the user-wide one to the callback, and then the -repo-specific one; by overwriting, the higher-priority repo-specific -value is left at the end). - -The `config_with_options` function lets the caller examine config -while adjusting some of the default behavior of `git_config`. It should -almost never be used by "regular" Git code that is looking up -configuration variables. It is intended for advanced callers like -`git-config`, which are intentionally tweaking the normal config-lookup -process. It takes two extra parameters: - -`config_source`:: -If this parameter is non-NULL, it specifies the source to parse for -configuration, rather than looking in the usual files. See `struct -git_config_source` in `config.h` for details. Regular `git_config` defaults -to `NULL`. - -`opts`:: -Specify options to adjust the behavior of parsing config files. See `struct -config_options` in `config.h` for details. As an example: regular `git_config` -sets `opts.respect_includes` to `1` by default. - -Reading Specific Files ----------------------- - -To read a specific file in git-config format, use -`git_config_from_file`. This takes the same callback and data parameters -as `git_config`. - -Querying For Specific Variables -------------------------------- - -For programs wanting to query for specific variables in a non-callback -manner, the config API provides two functions `git_config_get_value` -and `git_config_get_value_multi`. They both read values from an internal -cache generated previously from reading the config files. - -`int git_config_get_value(const char *key, const char **value)`:: - - Finds the highest-priority value for the configuration variable `key`, - stores the pointer to it in `value` and returns 0. When the - configuration variable `key` is not found, returns 1 without touching - `value`. The caller should not free or modify `value`, as it is owned - by the cache. - -`const struct string_list *git_config_get_value_multi(const char *key)`:: - - Finds and returns the value list, sorted in order of increasing priority - for the configuration variable `key`. When the configuration variable - `key` is not found, returns NULL. The caller should not free or modify - the returned pointer, as it is owned by the cache. - -`void git_config_clear(void)`:: - - Resets and invalidates the config cache. - -The config API also provides type specific API functions which do conversion -as well as retrieval for the queried variable, including: - -`int git_config_get_int(const char *key, int *dest)`:: - - Finds and parses the value to an integer for the configuration variable - `key`. Dies on error; otherwise, stores the value of the parsed integer in - `dest` and returns 0. When the configuration variable `key` is not found, - returns 1 without touching `dest`. - -`int git_config_get_ulong(const char *key, unsigned long *dest)`:: - - Similar to `git_config_get_int` but for unsigned longs. - -`int git_config_get_bool(const char *key, int *dest)`:: - - Finds and parses the value into a boolean value, for the configuration - variable `key` respecting keywords like "true" and "false". Integer - values are converted into true/false values (when they are non-zero or - zero, respectively). Other values cause a die(). If parsing is successful, - stores the value of the parsed result in `dest` and returns 0. When the - configuration variable `key` is not found, returns 1 without touching - `dest`. - -`int git_config_get_bool_or_int(const char *key, int *is_bool, int *dest)`:: - - Similar to `git_config_get_bool`, except that integers are copied as-is, - and `is_bool` flag is unset. - -`int git_config_get_maybe_bool(const char *key, int *dest)`:: - - Similar to `git_config_get_bool`, except that it returns -1 on error - rather than dying. - -`int git_config_get_string_const(const char *key, const char **dest)`:: - - Allocates and copies the retrieved string into the `dest` parameter for - the configuration variable `key`; if NULL string is given, prints an - error message and returns -1. When the configuration variable `key` is - not found, returns 1 without touching `dest`. - -`int git_config_get_string(const char *key, char **dest)`:: - - Similar to `git_config_get_string_const`, except that retrieved value - copied into the `dest` parameter is a mutable string. - -`int git_config_get_pathname(const char *key, const char **dest)`:: - - Similar to `git_config_get_string`, but expands `~` or `~user` into - the user's home directory when found at the beginning of the path. - -`git_die_config(const char *key, const char *err, ...)`:: - - First prints the error message specified by the caller in `err` and then - dies printing the line number and the file name of the highest priority - value for the configuration variable `key`. - -`void git_die_config_linenr(const char *key, const char *filename, int linenr)`:: - - Helper function which formats the die error message according to the - parameters entered. Used by `git_die_config()`. It can be used by callers - handling `git_config_get_value_multi()` to print the correct error message - for the desired value. - -See test-config.c for usage examples. - -Value Parsing Helpers ---------------------- - -To aid in parsing string values, the config API provides callbacks with -a number of helper functions, including: - -`git_config_int`:: -Parse the string to an integer, including unit factors. Dies on error; -otherwise, returns the parsed result. - -`git_config_ulong`:: -Identical to `git_config_int`, but for unsigned longs. - -`git_config_bool`:: -Parse a string into a boolean value, respecting keywords like "true" and -"false". Integer values are converted into true/false values (when they -are non-zero or zero, respectively). Other values cause a die(). If -parsing is successful, the return value is the result. - -`git_config_bool_or_int`:: -Same as `git_config_bool`, except that integers are returned as-is, and -an `is_bool` flag is unset. - -`git_parse_maybe_bool`:: -Same as `git_config_bool`, except that it returns -1 on error rather -than dying. - -`git_config_string`:: -Allocates and copies the value string into the `dest` parameter; if no -string is given, prints an error message and returns -1. - -`git_config_pathname`:: -Similar to `git_config_string`, but expands `~` or `~user` into the -user's home directory when found at the beginning of the path. - -Include Directives ------------------- - -By default, the config parser does not respect include directives. -However, a caller can use the special `git_config_include` wrapper -callback to support them. To do so, you simply wrap your "real" callback -function and data pointer in a `struct config_include_data`, and pass -the wrapper to the regular config-reading functions. For example: - -------------------------------------------- -int read_file_with_include(const char *file, config_fn_t fn, void *data) -{ - struct config_include_data inc = CONFIG_INCLUDE_INIT; - inc.fn = fn; - inc.data = data; - return git_config_from_file(git_config_include, file, &inc); -} -------------------------------------------- - -`git_config` respects includes automatically. The lower-level -`git_config_from_file` does not. - -Custom Configsets ------------------ - -A `config_set` can be used to construct an in-memory cache for -config-like files that the caller specifies (i.e., files like `.gitmodules`, -`~/.gitconfig` etc.). For example, - ----------------------------------------- -struct config_set gm_config; -git_configset_init(&gm_config); -int b; -/* we add config files to the config_set */ -git_configset_add_file(&gm_config, ".gitmodules"); -git_configset_add_file(&gm_config, ".gitmodules_alt"); - -if (!git_configset_get_bool(gm_config, "submodule.frotz.ignore", &b)) { - /* hack hack hack */ -} - -/* when we are done with the configset */ -git_configset_clear(&gm_config); ----------------------------------------- - -Configset API provides functions for the above mentioned work flow, including: - -`void git_configset_init(struct config_set *cs)`:: - - Initializes the config_set `cs`. - -`int git_configset_add_file(struct config_set *cs, const char *filename)`:: - - Parses the file and adds the variable-value pairs to the `config_set`, - dies if there is an error in parsing the file. Returns 0 on success, or - -1 if the file does not exist or is inaccessible. The user has to decide - if he wants to free the incomplete configset or continue using it when - the function returns -1. - -`int git_configset_get_value(struct config_set *cs, const char *key, const char **value)`:: - - Finds the highest-priority value for the configuration variable `key` - and config set `cs`, stores the pointer to it in `value` and returns 0. - When the configuration variable `key` is not found, returns 1 without - touching `value`. The caller should not free or modify `value`, as it - is owned by the cache. - -`const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key)`:: - - Finds and returns the value list, sorted in order of increasing priority - for the configuration variable `key` and config set `cs`. When the - configuration variable `key` is not found, returns NULL. The caller - should not free or modify the returned pointer, as it is owned by the cache. - -`void git_configset_clear(struct config_set *cs)`:: - - Clears `config_set` structure, removes all saved variable-value pairs. - -In addition to above functions, the `config_set` API provides type specific -functions in the vein of `git_config_get_int` and family but with an extra -parameter, pointer to struct `config_set`. -They all behave similarly to the `git_config_get*()` family described in -"Querying For Specific Variables" above. - -Writing Config Files --------------------- - -Git gives multiple entry points in the Config API to write config values to -files namely `git_config_set_in_file` and `git_config_set`, which write to -a specific config file or to `.git/config` respectively. They both take a -key/value pair as parameter. -In the end they both call `git_config_set_multivar_in_file` which takes four -parameters: - -- the name of the file, as a string, to which key/value pairs will be written. - -- the name of key, as a string. This is in canonical "flat" form: the section, - subsection, and variable segments will be separated by dots, and the section - and variable segments will be all lowercase. - E.g., `core.ignorecase`, `diff.SomeType.textconv`. - -- the value of the variable, as a string. If value is equal to NULL, it will - remove the matching key from the config file. - -- the value regex, as a string. It will disregard key/value pairs where value - does not match. - -- a multi_replace value, as an int. If value is equal to zero, nothing or only - one matching key/value is replaced, else all matching key/values (regardless - how many) are removed, before the new pair is written. - -It returns 0 on success. - -Also, there are functions `git_config_rename_section` and -`git_config_rename_section_in_file` with parameters `old_name` and `new_name` -for renaming or removing sections in the config files. If NULL is passed -through `new_name` parameter, the section will be removed from the config file. diff --git a/third_party/git/Documentation/technical/api-credentials.txt b/third_party/git/Documentation/technical/api-credentials.txt deleted file mode 100644 index 75368f26ca28..000000000000 --- a/third_party/git/Documentation/technical/api-credentials.txt +++ /dev/null @@ -1,271 +0,0 @@ -credentials API -=============== - -The credentials API provides an abstracted way of gathering username and -password credentials from the user (even though credentials in the wider -world can take many forms, in this document the word "credential" always -refers to a username and password pair). - -This document describes two interfaces: the C API that the credential -subsystem provides to the rest of Git, and the protocol that Git uses to -communicate with system-specific "credential helpers". If you are -writing Git code that wants to look up or prompt for credentials, see -the section "C API" below. If you want to write your own helper, see -the section on "Credential Helpers" below. - -Typical setup -------------- - ------------- -+-----------------------+ -| Git code (C) |--- to server requiring ---> -| | authentication -|.......................| -| C credential API |--- prompt ---> User -+-----------------------+ - ^ | - | pipe | - | v -+-----------------------+ -| Git credential helper | -+-----------------------+ ------------- - -The Git code (typically a remote-helper) will call the C API to obtain -credential data like a login/password pair (credential_fill). The -API will itself call a remote helper (e.g. "git credential-cache" or -"git credential-store") that may retrieve credential data from a -store. If the credential helper cannot find the information, the C API -will prompt the user. Then, the caller of the API takes care of -contacting the server, and does the actual authentication. - -C API ------ - -The credential C API is meant to be called by Git code which needs to -acquire or store a credential. It is centered around an object -representing a single credential and provides three basic operations: -fill (acquire credentials by calling helpers and/or prompting the user), -approve (mark a credential as successfully used so that it can be stored -for later use), and reject (mark a credential as unsuccessful so that it -can be erased from any persistent storage). - -Data Structures -~~~~~~~~~~~~~~~ - -`struct credential`:: - - This struct represents a single username/password combination - along with any associated context. All string fields should be - heap-allocated (or NULL if they are not known or not applicable). - The meaning of the individual context fields is the same as - their counterparts in the helper protocol; see the section below - for a description of each field. -+ -The `helpers` member of the struct is a `string_list` of helpers. Each -string specifies an external helper which will be run, in order, to -either acquire or store credentials. See the section on credential -helpers below. This list is filled-in by the API functions -according to the corresponding configuration variables before -consulting helpers, so there usually is no need for a caller to -modify the helpers field at all. -+ -This struct should always be initialized with `CREDENTIAL_INIT` or -`credential_init`. - - -Functions -~~~~~~~~~ - -`credential_init`:: - - Initialize a credential structure, setting all fields to empty. - -`credential_clear`:: - - Free any resources associated with the credential structure, - returning it to a pristine initialized state. - -`credential_fill`:: - - Instruct the credential subsystem to fill the username and - password fields of the passed credential struct by first - consulting helpers, then asking the user. After this function - returns, the username and password fields of the credential are - guaranteed to be non-NULL. If an error occurs, the function will - die(). - -`credential_reject`:: - - Inform the credential subsystem that the provided credentials - have been rejected. This will cause the credential subsystem to - notify any helpers of the rejection (which allows them, for - example, to purge the invalid credentials from storage). It - will also free() the username and password fields of the - credential and set them to NULL (readying the credential for - another call to `credential_fill`). Any errors from helpers are - ignored. - -`credential_approve`:: - - Inform the credential subsystem that the provided credentials - were successfully used for authentication. This will cause the - credential subsystem to notify any helpers of the approval, so - that they may store the result to be used again. Any errors - from helpers are ignored. - -`credential_from_url`:: - - Parse a URL into broken-down credential fields. - -Example -~~~~~~~ - -The example below shows how the functions of the credential API could be -used to login to a fictitious "foo" service on a remote host: - ------------------------------------------------------------------------ -int foo_login(struct foo_connection *f) -{ - int status; - /* - * Create a credential with some context; we don't yet know the - * username or password. - */ - - struct credential c = CREDENTIAL_INIT; - c.protocol = xstrdup("foo"); - c.host = xstrdup(f->hostname); - - /* - * Fill in the username and password fields by contacting - * helpers and/or asking the user. The function will die if it - * fails. - */ - credential_fill(&c); - - /* - * Otherwise, we have a username and password. Try to use it. - */ - status = send_foo_login(f, c.username, c.password); - switch (status) { - case FOO_OK: - /* It worked. Store the credential for later use. */ - credential_accept(&c); - break; - case FOO_BAD_LOGIN: - /* Erase the credential from storage so we don't try it - * again. */ - credential_reject(&c); - break; - default: - /* - * Some other error occurred. We don't know if the - * credential is good or bad, so report nothing to the - * credential subsystem. - */ - } - - /* Free any associated resources. */ - credential_clear(&c); - - return status; -} ------------------------------------------------------------------------ - - -Credential Helpers ------------------- - -Credential helpers are programs executed by Git to fetch or save -credentials from and to long-term storage (where "long-term" is simply -longer than a single Git process; e.g., credentials may be stored -in-memory for a few minutes, or indefinitely on disk). - -Each helper is specified by a single string in the configuration -variable `credential.helper` (and others, see linkgit:git-config[1]). -The string is transformed by Git into a command to be executed using -these rules: - - 1. If the helper string begins with "!", it is considered a shell - snippet, and everything after the "!" becomes the command. - - 2. Otherwise, if the helper string begins with an absolute path, the - verbatim helper string becomes the command. - - 3. Otherwise, the string "git credential-" is prepended to the helper - string, and the result becomes the command. - -The resulting command then has an "operation" argument appended to it -(see below for details), and the result is executed by the shell. - -Here are some example specifications: - ----------------------------------------------------- -# run "git credential-foo" -foo - -# same as above, but pass an argument to the helper -foo --bar=baz - -# the arguments are parsed by the shell, so use shell -# quoting if necessary -foo --bar="whitespace arg" - -# you can also use an absolute path, which will not use the git wrapper -/path/to/my/helper --with-arguments - -# or you can specify your own shell snippet -!f() { echo "password=`cat $HOME/.secret`"; }; f ----------------------------------------------------- - -Generally speaking, rule (3) above is the simplest for users to specify. -Authors of credential helpers should make an effort to assist their -users by naming their program "git-credential-$NAME", and putting it in -the $PATH or $GIT_EXEC_PATH during installation, which will allow a user -to enable it with `git config credential.helper $NAME`. - -When a helper is executed, it will have one "operation" argument -appended to its command line, which is one of: - -`get`:: - - Return a matching credential, if any exists. - -`store`:: - - Store the credential, if applicable to the helper. - -`erase`:: - - Remove a matching credential, if any, from the helper's storage. - -The details of the credential will be provided on the helper's stdin -stream. The exact format is the same as the input/output format of the -`git credential` plumbing command (see the section `INPUT/OUTPUT -FORMAT` in linkgit:git-credential[1] for a detailed specification). - -For a `get` operation, the helper should produce a list of attributes -on stdout in the same format. A helper is free to produce a subset, or -even no values at all if it has nothing useful to provide. Any provided -attributes will overwrite those already known about by Git. If a helper -outputs a `quit` attribute with a value of `true` or `1`, no further -helpers will be consulted, nor will the user be prompted (if no -credential has been provided, the operation will then fail). - -For a `store` or `erase` operation, the helper's output is ignored. -If it fails to perform the requested operation, it may complain to -stderr to inform the user. If it does not support the requested -operation (e.g., a read-only store), it should silently ignore the -request. - -If a helper receives any other operation, it should silently ignore the -request. This leaves room for future operations to be added (older -helpers will just ignore the new requests). - -See also --------- - -linkgit:gitcredentials[7] - -linkgit:git-config[1] (See configuration variables `credential.*`) diff --git a/third_party/git/Documentation/technical/api-diff.txt b/third_party/git/Documentation/technical/api-diff.txt deleted file mode 100644 index 30fc0e9c93b2..000000000000 --- a/third_party/git/Documentation/technical/api-diff.txt +++ /dev/null @@ -1,174 +0,0 @@ -diff API -======== - -The diff API is for programs that compare two sets of files (e.g. two -trees, one tree and the index) and present the found difference in -various ways. The calling program is responsible for feeding the API -pairs of files, one from the "old" set and the corresponding one from -"new" set, that are different. The library called through this API is -called diffcore, and is responsible for two things. - -* finding total rewrites (`-B`), renames (`-M`) and copies (`-C`), and - changes that touch a string (`-S`), as specified by the caller. - -* outputting the differences in various formats, as specified by the - caller. - -Calling sequence ----------------- - -* Prepare `struct diff_options` to record the set of diff options, and - then call `repo_diff_setup()` to initialize this structure. This - sets up the vanilla default. - -* Fill in the options structure to specify desired output format, rename - detection, etc. `diff_opt_parse()` can be used to parse options given - from the command line in a way consistent with existing git-diff - family of programs. - -* Call `diff_setup_done()`; this inspects the options set up so far for - internal consistency and make necessary tweaking to it (e.g. if - textual patch output was asked, recursive behaviour is turned on); - the callback set_default in diff_options can be used to tweak this more. - -* As you find different pairs of files, call `diff_change()` to feed - modified files, `diff_addremove()` to feed created or deleted files, - or `diff_unmerge()` to feed a file whose state is 'unmerged' to the - API. These are thin wrappers to a lower-level `diff_queue()` function - that is flexible enough to record any of these kinds of changes. - -* Once you finish feeding the pairs of files, call `diffcore_std()`. - This will tell the diffcore library to go ahead and do its work. - -* Calling `diff_flush()` will produce the output. - - -Data structures ---------------- - -* `struct diff_filespec` - -This is the internal representation for a single file (blob). It -records the blob object name (if known -- for a work tree file it -typically is a NUL SHA-1), filemode and pathname. This is what the -`diff_addremove()`, `diff_change()` and `diff_unmerge()` synthesize and -feed `diff_queue()` function with. - -* `struct diff_filepair` - -This records a pair of `struct diff_filespec`; the filespec for a file -in the "old" set (i.e. preimage) is called `one`, and the filespec for a -file in the "new" set (i.e. postimage) is called `two`. A change that -represents file creation has NULL in `one`, and file deletion has NULL -in `two`. - -A `filepair` starts pointing at `one` and `two` that are from the same -filename, but `diffcore_std()` can break pairs and match component -filespecs with other filespecs from a different filepair to form new -filepair. This is called 'rename detection'. - -* `struct diff_queue` - -This is a collection of filepairs. Notable members are: - -`queue`:: - - An array of pointers to `struct diff_filepair`. This - dynamically grows as you add filepairs; - -`alloc`:: - - The allocated size of the `queue` array; - -`nr`:: - - The number of elements in the `queue` array. - - -* `struct diff_options` - -This describes the set of options the calling program wants to affect -the operation of diffcore library with. - -Notable members are: - -`output_format`:: - The output format used when `diff_flush()` is run. - -`context`:: - Number of context lines to generate in patch output. - -`break_opt`, `detect_rename`, `rename-score`, `rename_limit`:: - Affects the way detection logic for complete rewrites, renames - and copies. - -`abbrev`:: - Number of hexdigits to abbreviate raw format output to. - -`pickaxe`:: - A constant string (can and typically does contain newlines to - look for a block of text, not just a single line) to filter out - the filepairs that do not change the number of strings contained - in its preimage and postimage of the diff_queue. - -`flags`:: - This is mostly a collection of boolean options that affects the - operation, but some do not have anything to do with the diffcore - library. - -`touched_flags`:: - Records whether a flag has been changed due to user request - (rather than just set/unset by default). - -`set_default`:: - Callback which allows tweaking the options in diff_setup_done(). - -BINARY, TEXT;; - Affects the way how a file that is seemingly binary is treated. - -FULL_INDEX;; - Tells the patch output format not to use abbreviated object - names on the "index" lines. - -FIND_COPIES_HARDER;; - Tells the diffcore library that the caller is feeding unchanged - filepairs to allow copies from unmodified files be detected. - -COLOR_DIFF;; - Output should be colored. - -COLOR_DIFF_WORDS;; - Output is a colored word-diff. - -NO_INDEX;; - Tells diff-files that the input is not tracked files but files - in random locations on the filesystem. - -ALLOW_EXTERNAL;; - Tells output routine that it is Ok to call user specified patch - output routine. Plumbing disables this to ensure stable output. - -QUIET;; - Do not show any output. - -REVERSE_DIFF;; - Tells the library that the calling program is feeding the - filepairs reversed; `one` is two, and `two` is one. - -EXIT_WITH_STATUS;; - For communication between the calling program and the options - parser; tell the calling program to signal the presence of - difference using program exit code. - -HAS_CHANGES;; - Internal; used for optimization to see if there is any change. - -SILENT_ON_REMOVE;; - Affects if diff-files shows removed files. - -RECURSIVE, TREE_IN_RECURSIVE;; - Tells if tree traversal done by tree-diff should recursively - descend into a tree object pair that are different in preimage - and postimage set. - -(JC) diff --git a/third_party/git/Documentation/technical/api-directory-listing.txt b/third_party/git/Documentation/technical/api-directory-listing.txt deleted file mode 100644 index 5abb8e8b1fdb..000000000000 --- a/third_party/git/Documentation/technical/api-directory-listing.txt +++ /dev/null @@ -1,130 +0,0 @@ -directory listing API -===================== - -The directory listing API is used to enumerate paths in the work tree, -optionally taking `.git/info/exclude` and `.gitignore` files per -directory into account. - -Data structure --------------- - -`struct dir_struct` structure is used to pass directory traversal -options to the library and to record the paths discovered. A single -`struct dir_struct` is used regardless of whether or not the traversal -recursively descends into subdirectories. - -The notable options are: - -`exclude_per_dir`:: - - The name of the file to be read in each directory for excluded - files (typically `.gitignore`). - -`flags`:: - - A bit-field of options: - -`DIR_SHOW_IGNORED`::: - - Return just ignored files in `entries[]`, not untracked - files. This flag is mutually exclusive with - `DIR_SHOW_IGNORED_TOO`. - -`DIR_SHOW_IGNORED_TOO`::: - - Similar to `DIR_SHOW_IGNORED`, but return ignored files in - `ignored[]` in addition to untracked files in - `entries[]`. This flag is mutually exclusive with - `DIR_SHOW_IGNORED`. - -`DIR_KEEP_UNTRACKED_CONTENTS`::: - - Only has meaning if `DIR_SHOW_IGNORED_TOO` is also set; if this is set, the - untracked contents of untracked directories are also returned in - `entries[]`. - -`DIR_SHOW_IGNORED_TOO_MODE_MATCHING`::: - - Only has meaning if `DIR_SHOW_IGNORED_TOO` is also set; if - this is set, returns ignored files and directories that match - an exclude pattern. If a directory matches an exclude pattern, - then the directory is returned and the contained paths are - not. A directory that does not match an exclude pattern will - not be returned even if all of its contents are ignored. In - this case, the contents are returned as individual entries. -+ -If this is set, files and directories that explicitly match an ignore -pattern are reported. Implicitly ignored directories (directories that -do not match an ignore pattern, but whose contents are all ignored) -are not reported, instead all of the contents are reported. - -`DIR_COLLECT_IGNORED`::: - - Special mode for git-add. Return ignored files in `ignored[]` and - untracked files in `entries[]`. Only returns ignored files that match - pathspec exactly (no wildcards). Does not recurse into ignored - directories. - -`DIR_SHOW_OTHER_DIRECTORIES`::: - - Include a directory that is not tracked. - -`DIR_HIDE_EMPTY_DIRECTORIES`::: - - Do not include a directory that is not tracked and is empty. - -`DIR_NO_GITLINKS`::: - - If set, recurse into a directory that looks like a Git - directory. Otherwise it is shown as a directory. - -The result of the enumeration is left in these fields: - -`entries[]`:: - - An array of `struct dir_entry`, each element of which describes - a path. - -`nr`:: - - The number of members in `entries[]` array. - -`alloc`:: - - Internal use; keeps track of allocation of `entries[]` array. - -`ignored[]`:: - - An array of `struct dir_entry`, used for ignored paths with the - `DIR_SHOW_IGNORED_TOO` and `DIR_COLLECT_IGNORED` flags. - -`ignored_nr`:: - - The number of members in `ignored[]` array. - -Calling sequence ----------------- - -Note: index may be looked at for .gitignore files that are CE_SKIP_WORKTREE -marked. If you to exclude files, make sure you have loaded index first. - -* Prepare `struct dir_struct dir` and clear it with `memset(&dir, 0, - sizeof(dir))`. - -* To add single exclude pattern, call `add_exclude_list()` and then - `add_exclude()`. - -* To add patterns from a file (e.g. `.git/info/exclude`), call - `add_excludes_from_file()` , and/or set `dir.exclude_per_dir`. A - short-hand function `setup_standard_excludes()` can be used to set - up the standard set of exclude settings. - -* Set options described in the Data Structure section above. - -* Call `read_directory()`. - -* Use `dir.entries[]`. - -* Call `clear_directory()` when none of the contained elements are no longer in use. - -(JC) diff --git a/third_party/git/Documentation/technical/api-gitattributes.txt b/third_party/git/Documentation/technical/api-gitattributes.txt deleted file mode 100644 index 45f0df600fab..000000000000 --- a/third_party/git/Documentation/technical/api-gitattributes.txt +++ /dev/null @@ -1,154 +0,0 @@ -gitattributes API -================= - -gitattributes mechanism gives a uniform way to associate various -attributes to set of paths. - - -Data Structure --------------- - -`struct git_attr`:: - - An attribute is an opaque object that is identified by its name. - Pass the name to `git_attr()` function to obtain the object of - this type. The internal representation of this structure is - of no interest to the calling programs. The name of the - attribute can be retrieved by calling `git_attr_name()`. - -`struct attr_check_item`:: - - This structure represents one attribute and its value. - -`struct attr_check`:: - - This structure represents a collection of `attr_check_item`. - It is passed to `git_check_attr()` function, specifying the - attributes to check, and receives their values. - - -Attribute Values ----------------- - -An attribute for a path can be in one of four states: Set, Unset, -Unspecified or set to a string, and `.value` member of `struct -attr_check_item` records it. There are three macros to check these: - -`ATTR_TRUE()`:: - - Returns true if the attribute is Set for the path. - -`ATTR_FALSE()`:: - - Returns true if the attribute is Unset for the path. - -`ATTR_UNSET()`:: - - Returns true if the attribute is Unspecified for the path. - -If none of the above returns true, `.value` member points at a string -value of the attribute for the path. - - -Querying Specific Attributes ----------------------------- - -* Prepare `struct attr_check` using attr_check_initl() - function, enumerating the names of attributes whose values you are - interested in, terminated with a NULL pointer. Alternatively, an - empty `struct attr_check` can be prepared by calling - `attr_check_alloc()` function and then attributes you want to - ask about can be added to it with `attr_check_append()` - function. - -* Call `git_check_attr()` to check the attributes for the path. - -* Inspect `attr_check` structure to see how each of the - attribute in the array is defined for the path. - - -Example -------- - -To see how attributes "crlf" and "ident" are set for different paths. - -. Prepare a `struct attr_check` with two elements (because - we are checking two attributes): - ------------- -static struct attr_check *check; -static void setup_check(void) -{ - if (check) - return; /* already done */ - check = attr_check_initl("crlf", "ident", NULL); -} ------------- - -. Call `git_check_attr()` with the prepared `struct attr_check`: - ------------- - const char *path; - - setup_check(); - git_check_attr(path, check); ------------- - -. Act on `.value` member of the result, left in `check->items[]`: - ------------- - const char *value = check->items[0].value; - - if (ATTR_TRUE(value)) { - The attribute is Set, by listing only the name of the - attribute in the gitattributes file for the path. - } else if (ATTR_FALSE(value)) { - The attribute is Unset, by listing the name of the - attribute prefixed with a dash - for the path. - } else if (ATTR_UNSET(value)) { - The attribute is neither set nor unset for the path. - } else if (!strcmp(value, "input")) { - If none of ATTR_TRUE(), ATTR_FALSE(), or ATTR_UNSET() is - true, the value is a string set in the gitattributes - file for the path by saying "attr=value". - } else if (... other check using value as string ...) { - ... - } ------------- - -To see how attributes in argv[] are set for different paths, only -the first step in the above would be different. - ------------- -static struct attr_check *check; -static void setup_check(const char **argv) -{ - check = attr_check_alloc(); - while (*argv) { - struct git_attr *attr = git_attr(*argv); - attr_check_append(check, attr); - argv++; - } -} ------------- - - -Querying All Attributes ------------------------ - -To get the values of all attributes associated with a file: - -* Prepare an empty `attr_check` structure by calling - `attr_check_alloc()`. - -* Call `git_all_attrs()`, which populates the `attr_check` - with the attributes attached to the path. - -* Iterate over the `attr_check.items[]` array to examine - the attribute names and values. The name of the attribute - described by an `attr_check.items[]` object can be retrieved via - `git_attr_name(check->items[i].attr)`. (Please note that no items - will be returned for unset attributes, so `ATTR_UNSET()` will return - false for all returned `attr_check.items[]` objects.) - -* Free the `attr_check` struct by calling `attr_check_free()`. diff --git a/third_party/git/Documentation/technical/api-grep.txt b/third_party/git/Documentation/technical/api-grep.txt deleted file mode 100644 index a69cc8964d58..000000000000 --- a/third_party/git/Documentation/technical/api-grep.txt +++ /dev/null @@ -1,8 +0,0 @@ -grep API -======== - -Talk about <grep.h>, things like: - -* grep_buffer() - -(JC) diff --git a/third_party/git/Documentation/technical/api-history-graph.txt b/third_party/git/Documentation/technical/api-history-graph.txt deleted file mode 100644 index d0d1707c8c88..000000000000 --- a/third_party/git/Documentation/technical/api-history-graph.txt +++ /dev/null @@ -1,173 +0,0 @@ -history graph API -================= - -The graph API is used to draw a text-based representation of the commit -history. The API generates the graph in a line-by-line fashion. - -Functions ---------- - -Core functions: - -* `graph_init()` creates a new `struct git_graph` - -* `graph_update()` moves the graph to a new commit. - -* `graph_next_line()` outputs the next line of the graph into a strbuf. It - does not add a terminating newline. - -* `graph_padding_line()` outputs a line of vertical padding in the graph. It - is similar to `graph_next_line()`, but is guaranteed to never print the line - containing the current commit. Where `graph_next_line()` would print the - commit line next, `graph_padding_line()` prints a line that simply extends - all branch lines downwards one row, leaving their positions unchanged. - -* `graph_is_commit_finished()` determines if the graph has output all lines - necessary for the current commit. If `graph_update()` is called before all - lines for the current commit have been printed, the next call to - `graph_next_line()` will output an ellipsis, to indicate that a portion of - the graph was omitted. - -The following utility functions are wrappers around `graph_next_line()` and -`graph_is_commit_finished()`. They always print the output to stdout. -They can all be called with a NULL graph argument, in which case no graph -output will be printed. - -* `graph_show_commit()` calls `graph_next_line()` and - `graph_is_commit_finished()` until one of them return non-zero. This prints - all graph lines up to, and including, the line containing this commit. - Output is printed to stdout. The last line printed does not contain a - terminating newline. - -* `graph_show_oneline()` calls `graph_next_line()` and prints the result to - stdout. The line printed does not contain a terminating newline. - -* `graph_show_padding()` calls `graph_padding_line()` and prints the result to - stdout. The line printed does not contain a terminating newline. - -* `graph_show_remainder()` calls `graph_next_line()` until - `graph_is_commit_finished()` returns non-zero. Output is printed to stdout. - The last line printed does not contain a terminating newline. Returns 1 if - output was printed, and 0 if no output was necessary. - -* `graph_show_strbuf()` prints the specified strbuf to stdout, prefixing all - lines but the first with a graph line. The caller is responsible for - ensuring graph output for the first line has already been printed to stdout. - (This can be done with `graph_show_commit()` or `graph_show_oneline()`.) If - a NULL graph is supplied, the strbuf is printed as-is. - -* `graph_show_commit_msg()` is similar to `graph_show_strbuf()`, but it also - prints the remainder of the graph, if more lines are needed after the strbuf - ends. It is better than directly calling `graph_show_strbuf()` followed by - `graph_show_remainder()` since it properly handles buffers that do not end in - a terminating newline. The output printed by `graph_show_commit_msg()` will - end in a newline if and only if the strbuf ends in a newline. - -Data structure --------------- -`struct git_graph` is an opaque data type used to store the current graph -state. - -Calling sequence ----------------- - -* Create a `struct git_graph` by calling `graph_init()`. When using the - revision walking API, this is done automatically by `setup_revisions()` if - the '--graph' option is supplied. - -* Use the revision walking API to walk through a group of contiguous commits. - The `get_revision()` function automatically calls `graph_update()` each time - it is invoked. - -* For each commit, call `graph_next_line()` repeatedly, until - `graph_is_commit_finished()` returns non-zero. Each call to - `graph_next_line()` will output a single line of the graph. The resulting - lines will not contain any newlines. `graph_next_line()` returns 1 if the - resulting line contains the current commit, or 0 if this is merely a line - needed to adjust the graph before or after the current commit. This return - value can be used to determine where to print the commit summary information - alongside the graph output. - -Limitations ------------ - -* `graph_update()` must be called with commits in topological order. It should - not be called on a commit if it has already been invoked with an ancestor of - that commit, or the graph output will be incorrect. - -* `graph_update()` must be called on a contiguous group of commits. If - `graph_update()` is called on a particular commit, it should later be called - on all parents of that commit. Parents must not be skipped, or the graph - output will appear incorrect. -+ -`graph_update()` may be used on a pruned set of commits only if the parent list -has been rewritten so as to include only ancestors from the pruned set. - -* The graph API does not currently support reverse commit ordering. In - order to implement reverse ordering, the graphing API needs an - (efficient) mechanism to find the children of a commit. - -Sample usage ------------- - ------------- -struct commit *commit; -struct git_graph *graph = graph_init(opts); - -while ((commit = get_revision(opts)) != NULL) { - while (!graph_is_commit_finished(graph)) - { - struct strbuf sb; - int is_commit_line; - - strbuf_init(&sb, 0); - is_commit_line = graph_next_line(graph, &sb); - fputs(sb.buf, stdout); - - if (is_commit_line) - log_tree_commit(opts, commit); - else - putchar(opts->diffopt.line_termination); - } -} ------------- - -Sample output -------------- - -The following is an example of the output from the graph API. This output does -not include any commit summary information--callers are responsible for -outputting that information, if desired. - ------------- -* -* -* -|\ -* | -| | * -| \ \ -| \ \ -*-. \ \ -|\ \ \ \ -| | * | | -| | | | | * -| | | | | * -| | | | | * -| | | | | |\ -| | | | | | * -| * | | | | | -| | | | | * \ -| | | | | |\ | -| | | | * | | | -| | | | * | | | -* | | | | | | | -| |/ / / / / / -|/| / / / / / -* | | | | | | -|/ / / / / / -* | | | | | -| | | | | * -| | | | |/ -| | | | * ------------- diff --git a/third_party/git/Documentation/technical/api-merge.txt b/third_party/git/Documentation/technical/api-merge.txt index 9dc1bed768a4..487d4d83fff2 100644 --- a/third_party/git/Documentation/technical/api-merge.txt +++ b/third_party/git/Documentation/technical/api-merge.txt @@ -28,77 +28,9 @@ and `diff.c` for examples. * `struct ll_merge_options` -This describes the set of options the calling program wants to affect -the operation of a low-level (single file) merge. Some options: - -`virtual_ancestor`:: - Behave as though this were part of a merge between common - ancestors in a recursive merge. - If a helper program is specified by the - `[merge "<driver>"] recursive` configuration, it will - be used (see linkgit:gitattributes[5]). - -`variant`:: - Resolve local conflicts automatically in favor - of one side or the other (as in 'git merge-file' - `--ours`/`--theirs`/`--union`). Can be `0`, - `XDL_MERGE_FAVOR_OURS`, `XDL_MERGE_FAVOR_THEIRS`, or - `XDL_MERGE_FAVOR_UNION`. - -`renormalize`:: - Resmudge and clean the "base", "theirs" and "ours" files - before merging. Use this when the merge is likely to have - overlapped with a change in smudge/clean or end-of-line - normalization rules. +Check ll-merge.h for details. Low-level (single file) merge ----------------------------- -`ll_merge`:: - - Perform a three-way single-file merge in core. This is - a thin wrapper around `xdl_merge` that takes the path and - any merge backend specified in `.gitattributes` or - `.git/info/attributes` into account. Returns 0 for a - clean merge. - -Calling sequence: - -* Prepare a `struct ll_merge_options` to record options. - If you have no special requests, skip this and pass `NULL` - as the `opts` parameter to use the default options. - -* Allocate an mmbuffer_t variable for the result. - -* Allocate and fill variables with the file's original content - and two modified versions (using `read_mmfile`, for example). - -* Call `ll_merge()`. - -* Read the merged content from `result_buf.ptr` and `result_buf.size`. - -* Release buffers when finished. A simple - `free(ancestor.ptr); free(ours.ptr); free(theirs.ptr); - free(result_buf.ptr);` will do. - -If the modifications do not merge cleanly, `ll_merge` will return a -nonzero value and `result_buf` will generally include a description of -the conflict bracketed by markers such as the traditional `<<<<<<<` -and `>>>>>>>`. - -The `ancestor_label`, `our_label`, and `their_label` parameters are -used to label the different sides of a conflict if the merge driver -supports this. - -Everything else ---------------- - -Talk about <merge-recursive.h> and merge_file(): - - - merge_trees() to merge with rename detection - - merge_recursive() for ancestor consolidation - - try_merge_command() for other strategies - - conflict format - - merge options - -(Daniel, Miklos, Stephan, JC) +Check ll-merge.h for details. diff --git a/third_party/git/Documentation/technical/api-object-access.txt b/third_party/git/Documentation/technical/api-object-access.txt deleted file mode 100644 index 5b29622d00ea..000000000000 --- a/third_party/git/Documentation/technical/api-object-access.txt +++ /dev/null @@ -1,15 +0,0 @@ -object access API -================= - -Talk about <sha1-file.c> and <object.h> family, things like - -* read_sha1_file() -* read_object_with_reference() -* has_sha1_file() -* write_sha1_file() -* pretend_object_file() -* lookup_{object,commit,tag,blob,tree} -* parse_{object,commit,tag,blob,tree} -* Use of object flags - -(JC, Shawn, Daniel, Dscho, Linus) diff --git a/third_party/git/Documentation/technical/api-oid-array.txt b/third_party/git/Documentation/technical/api-oid-array.txt deleted file mode 100644 index c97428c2c349..000000000000 --- a/third_party/git/Documentation/technical/api-oid-array.txt +++ /dev/null @@ -1,90 +0,0 @@ -oid-array API -============== - -The oid-array API provides storage and manipulation of sets of object -identifiers. The emphasis is on storage and processing efficiency, -making them suitable for large lists. Note that the ordering of items is -not preserved over some operations. - -Data Structures ---------------- - -`struct oid_array`:: - - A single array of object IDs. This should be initialized by - assignment from `OID_ARRAY_INIT`. The `oid` member contains - the actual data. The `nr` member contains the number of items in - the set. The `alloc` and `sorted` members are used internally, - and should not be needed by API callers. - -Functions ---------- - -`oid_array_append`:: - Add an item to the set. The object ID will be placed at the end of - the array (but note that some operations below may lose this - ordering). - -`oid_array_lookup`:: - Perform a binary search of the array for a specific object ID. - If found, returns the offset (in number of elements) of the - object ID. If not found, returns a negative integer. If the array - is not sorted, this function has the side effect of sorting it. - -`oid_array_clear`:: - Free all memory associated with the array and return it to the - initial, empty state. - -`oid_array_for_each`:: - Iterate over each element of the list, executing the callback - function for each one. Does not sort the list, so any custom - hash order is retained. If the callback returns a non-zero - value, the iteration ends immediately and the callback's - return is propagated; otherwise, 0 is returned. - -`oid_array_for_each_unique`:: - Iterate over each unique element of the list in sorted order, - but otherwise behave like `oid_array_for_each`. If the array - is not sorted, this function has the side effect of sorting - it. - -`oid_array_filter`:: - Apply the callback function `want` to each entry in the array, - retaining only the entries for which the function returns true. - Preserve the order of the entries that are retained. - -Examples --------- - ------------------------------------------ -int print_callback(const struct object_id *oid, - void *data) -{ - printf("%s\n", oid_to_hex(oid)); - return 0; /* always continue */ -} - -void some_func(void) -{ - struct sha1_array hashes = OID_ARRAY_INIT; - struct object_id oid; - - /* Read objects into our set */ - while (read_object_from_stdin(oid.hash)) - oid_array_append(&hashes, &oid); - - /* Check if some objects are in our set */ - while (read_object_from_stdin(oid.hash)) { - if (oid_array_lookup(&hashes, &oid) >= 0) - printf("it's in there!\n"); - - /* - * Print the unique set of objects. We could also have - * avoided adding duplicate objects in the first place, - * but we would end up re-sorting the array repeatedly. - * Instead, this will sort once and then skip duplicates - * in linear time. - */ - oid_array_for_each_unique(&hashes, print_callback, NULL); -} ------------------------------------------ diff --git a/third_party/git/Documentation/technical/api-parse-options.txt b/third_party/git/Documentation/technical/api-parse-options.txt index 2e2e7c10c620..5a60bbfa7f41 100644 --- a/third_party/git/Documentation/technical/api-parse-options.txt +++ b/third_party/git/Documentation/technical/api-parse-options.txt @@ -232,9 +232,9 @@ There are some macros to easily define options: will be overwritten, so this should only be used for options where the last one specified on the command line wins. -`OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`:: +`OPT_PASSTHRU_ARGV(short, long, &strvec_var, arg_str, description, flags)`:: Introduce an option where all instances of it on the command-line will - be reconstructed into an argv_array. This is useful when you need to + be reconstructed into a strvec. This is useful when you need to pass the command-line option, which can be specified multiple times, to another command. diff --git a/third_party/git/Documentation/technical/api-quote.txt b/third_party/git/Documentation/technical/api-quote.txt deleted file mode 100644 index e8a1bce94e05..000000000000 --- a/third_party/git/Documentation/technical/api-quote.txt +++ /dev/null @@ -1,10 +0,0 @@ -quote API -========= - -Talk about <quote.h>, things like - -* sq_quote and unquote -* c_style quote and unquote -* quoting for foreign languages - -(JC) diff --git a/third_party/git/Documentation/technical/api-ref-iteration.txt b/third_party/git/Documentation/technical/api-ref-iteration.txt deleted file mode 100644 index ad9d019ff9b4..000000000000 --- a/third_party/git/Documentation/technical/api-ref-iteration.txt +++ /dev/null @@ -1,78 +0,0 @@ -ref iteration API -================= - - -Iteration of refs is done by using an iterate function which will call a -callback function for every ref. The callback function has this -signature: - - int handle_one_ref(const char *refname, const struct object_id *oid, - int flags, void *cb_data); - -There are different kinds of iterate functions which all take a -callback of this type. The callback is then called for each found ref -until the callback returns nonzero. The returned value is then also -returned by the iterate function. - -Iteration functions -------------------- - -* `head_ref()` just iterates the head ref. - -* `for_each_ref()` iterates all refs. - -* `for_each_ref_in()` iterates all refs which have a defined prefix and - strips that prefix from the passed variable refname. - -* `for_each_tag_ref()`, `for_each_branch_ref()`, `for_each_remote_ref()`, - `for_each_replace_ref()` iterate refs from the respective area. - -* `for_each_glob_ref()` iterates all refs that match the specified glob - pattern. - -* `for_each_glob_ref_in()` the previous and `for_each_ref_in()` combined. - -* Use `refs_` API for accessing submodules. The submodule ref store could - be obtained with `get_submodule_ref_store()`. - -* `for_each_rawref()` can be used to learn about broken ref and symref. - -* `for_each_reflog()` iterates each reflog file. - -Submodules ----------- - -If you want to iterate the refs of a submodule you first need to add the -submodules object database. You can do this by a code-snippet like -this: - - const char *path = "path/to/submodule" - if (add_submodule_odb(path)) - die("Error submodule '%s' not populated.", path); - -`add_submodule_odb()` will return zero on success. If you -do not do this you will get an error for each ref that it does not point -to a valid object. - -Note: As a side-effect of this you cannot safely assume that all -objects you lookup are available in superproject. All submodule objects -will be available the same way as the superprojects objects. - -Example: --------- - ----- -static int handle_remote_ref(const char *refname, - const unsigned char *sha1, int flags, void *cb_data) -{ - struct strbuf *output = cb_data; - strbuf_addf(output, "%s\n", refname); - return 0; -} - -... - - struct strbuf output = STRBUF_INIT; - for_each_remote_ref(handle_remote_ref, &output); - printf("%s", output.buf); ----- diff --git a/third_party/git/Documentation/technical/api-remote.txt b/third_party/git/Documentation/technical/api-remote.txt deleted file mode 100644 index f10941b2e816..000000000000 --- a/third_party/git/Documentation/technical/api-remote.txt +++ /dev/null @@ -1,127 +0,0 @@ -Remotes configuration API -========================= - -The API in remote.h gives access to the configuration related to -remotes. It handles all three configuration mechanisms historically -and currently used by Git, and presents the information in a uniform -fashion. Note that the code also handles plain URLs without any -configuration, giving them just the default information. - -struct remote -------------- - -`name`:: - - The user's nickname for the remote - -`url`:: - - An array of all of the url_nr URLs configured for the remote - -`pushurl`:: - - An array of all of the pushurl_nr push URLs configured for the remote - -`push`:: - - An array of refspecs configured for pushing, with - push_refspec being the literal strings, and push_refspec_nr - being the quantity. - -`fetch`:: - - An array of refspecs configured for fetching, with - fetch_refspec being the literal strings, and fetch_refspec_nr - being the quantity. - -`fetch_tags`:: - - The setting for whether to fetch tags (as a separate rule from - the configured refspecs); -1 means never to fetch tags, 0 - means to auto-follow tags based on the default heuristic, 1 - means to always auto-follow tags, and 2 means to fetch all - tags. - -`receivepack`, `uploadpack`:: - - The configured helper programs to run on the remote side, for - Git-native protocols. - -`http_proxy`:: - - The proxy to use for curl (http, https, ftp, etc.) URLs. - -`http_proxy_authmethod`:: - - The method used for authenticating against `http_proxy`. - -struct remotes can be found by name with remote_get(), and iterated -through with for_each_remote(). remote_get(NULL) will return the -default remote, given the current branch and configuration. - -struct refspec --------------- - -A struct refspec holds the parsed interpretation of a refspec. If it -will force updates (starts with a '+'), force is true. If it is a -pattern (sides end with '*') pattern is true. src and dest are the -two sides (including '*' characters if present); if there is only one -side, it is src, and dst is NULL; if sides exist but are empty (i.e., -the refspec either starts or ends with ':'), the corresponding side is -"". - -An array of strings can be parsed into an array of struct refspecs -using parse_fetch_refspec() or parse_push_refspec(). - -remote_find_tracking(), given a remote and a struct refspec with -either src or dst filled out, will fill out the other such that the -result is in the "fetch" specification for the remote (note that this -evaluates patterns and returns a single result). - -struct branch -------------- - -Note that this may end up moving to branch.h - -struct branch holds the configuration for a branch. It can be looked -up with branch_get(name) for "refs/heads/{name}", or with -branch_get(NULL) for HEAD. - -It contains: - -`name`:: - - The short name of the branch. - -`refname`:: - - The full path for the branch ref. - -`remote_name`:: - - The name of the remote listed in the configuration. - -`merge_name`:: - - An array of the "merge" lines in the configuration. - -`merge`:: - - An array of the struct refspecs used for the merge lines. That - is, merge[i]->dst is a local tracking ref which should be - merged into this branch by default. - -`merge_nr`:: - - The number of merge configurations - -branch_has_merge_config() returns true if the given branch has merge -configuration given. - -Other stuff ------------ - -There is other stuff in remote.h that is related, in general, to the -process of interacting with remotes. - -(Daniel Barkalow) diff --git a/third_party/git/Documentation/technical/api-revision-walking.txt b/third_party/git/Documentation/technical/api-revision-walking.txt deleted file mode 100644 index 03f9ea6ac4ba..000000000000 --- a/third_party/git/Documentation/technical/api-revision-walking.txt +++ /dev/null @@ -1,72 +0,0 @@ -revision walking API -==================== - -The revision walking API offers functions to build a list of revisions -and then iterate over that list. - -Calling sequence ----------------- - -The walking API has a given calling sequence: first you need to -initialize a rev_info structure, then add revisions to control what kind -of revision list do you want to get, finally you can iterate over the -revision list. - -Functions ---------- - -`repo_init_revisions`:: - - Initialize a rev_info structure with default values. The third - parameter may be NULL or can be prefix path, and then the `.prefix` - variable will be set to it. This is typically the first function you - want to call when you want to deal with a revision list. After calling - this function, you are free to customize options, like set - `.ignore_merges` to 0 if you don't want to ignore merges, and so on. See - `revision.h` for a complete list of available options. - -`add_pending_object`:: - - This function can be used if you want to add commit objects as revision - information. You can use the `UNINTERESTING` object flag to indicate if - you want to include or exclude the given commit (and commits reachable - from the given commit) from the revision list. -+ -NOTE: If you have the commits as a string list then you probably want to -use setup_revisions(), instead of parsing each string and using this -function. - -`setup_revisions`:: - - Parse revision information, filling in the `rev_info` structure, and - removing the used arguments from the argument list. Returns the number - of arguments left that weren't recognized, which are also moved to the - head of the argument list. The last parameter is used in case no - parameter given by the first two arguments. - -`prepare_revision_walk`:: - - Prepares the rev_info structure for a walk. You should check if it - returns any error (non-zero return code) and if it does not, you can - start using get_revision() to do the iteration. - -`get_revision`:: - - Takes a pointer to a `rev_info` structure and iterates over it, - returning a `struct commit *` each time you call it. The end of the - revision list is indicated by returning a NULL pointer. - -`reset_revision_walk`:: - - Reset the flags used by the revision walking api. You can use - this to do multiple sequential revision walks. - -Data structures ---------------- - -Talk about <revision.h>, things like: - -* two diff_options, one for path limiting, another for output; -* remaining functions; - -(Linus, JC, Dscho) diff --git a/third_party/git/Documentation/technical/api-run-command.txt b/third_party/git/Documentation/technical/api-run-command.txt deleted file mode 100644 index 8bf3e37f5375..000000000000 --- a/third_party/git/Documentation/technical/api-run-command.txt +++ /dev/null @@ -1,264 +0,0 @@ -run-command API -=============== - -The run-command API offers a versatile tool to run sub-processes with -redirected input and output as well as with a modified environment -and an alternate current directory. - -A similar API offers the capability to run a function asynchronously, -which is primarily used to capture the output that the function -produces in the caller in order to process it. - - -Functions ---------- - -`child_process_init`:: - - Initialize a struct child_process variable. - -`start_command`:: - - Start a sub-process. Takes a pointer to a `struct child_process` - that specifies the details and returns pipe FDs (if requested). - See below for details. - -`finish_command`:: - - Wait for the completion of a sub-process that was started with - start_command(). - -`run_command`:: - - A convenience function that encapsulates a sequence of - start_command() followed by finish_command(). Takes a pointer - to a `struct child_process` that specifies the details. - -`run_command_v_opt`, `run_command_v_opt_cd_env`:: - - Convenience functions that encapsulate a sequence of - start_command() followed by finish_command(). The argument argv - specifies the program and its arguments. The argument opt is zero - or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`, - `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE` - that correspond to the members .no_stdin, .git_cmd, - .stdout_to_stderr, .silent_exec_failure of `struct child_process`. - The argument dir corresponds the member .dir. The argument env - corresponds to the member .env. - -`child_process_clear`:: - - Release the memory associated with the struct child_process. - Most users of the run-command API don't need to call this - function explicitly because `start_command` invokes it on - failure and `finish_command` calls it automatically already. - -The functions above do the following: - -. If a system call failed, errno is set and -1 is returned. A diagnostic - is printed. - -. If the program was not found, then -1 is returned and errno is set to - ENOENT; a diagnostic is printed only if .silent_exec_failure is 0. - -. Otherwise, the program is run. If it terminates regularly, its exit - code is returned. No diagnostic is printed, even if the exit code is - non-zero. - -. If the program terminated due to a signal, then the return value is the - signal number + 128, ie. the same value that a POSIX shell's $? would - report. A diagnostic is printed. - - -`start_async`:: - - Run a function asynchronously. Takes a pointer to a `struct - async` that specifies the details and returns a set of pipe FDs - for communication with the function. See below for details. - -`finish_async`:: - - Wait for the completion of an asynchronous function that was - started with start_async(). - -`run_hook`:: - - Run a hook. - The first argument is a pathname to an index file, or NULL - if the hook uses the default index file or no index is needed. - The second argument is the name of the hook. - The further arguments correspond to the hook arguments. - The last argument has to be NULL to terminate the arguments list. - If the hook does not exist or is not executable, the return - value will be zero. - If it is executable, the hook will be executed and the exit - status of the hook is returned. - On execution, .stdout_to_stderr and .no_stdin will be set. - (See below.) - - -Data structures ---------------- - -* `struct child_process` - -This describes the arguments, redirections, and environment of a -command to run in a sub-process. - -The caller: - -1. allocates and clears (using child_process_init() or - CHILD_PROCESS_INIT) a struct child_process variable; -2. initializes the members; -3. calls start_command(); -4. processes the data; -5. closes file descriptors (if necessary; see below); -6. calls finish_command(). - -The .argv member is set up as an array of string pointers (NULL -terminated), of which .argv[0] is the program name to run (usually -without a path). If the command to run is a git command, set argv[0] to -the command name without the 'git-' prefix and set .git_cmd = 1. - -Note that the ownership of the memory pointed to by .argv stays with the -caller, but it should survive until `finish_command` completes. If the -.argv member is NULL, `start_command` will point it at the .args -`argv_array` (so you may use one or the other, but you must use exactly -one). The memory in .args will be cleaned up automatically during -`finish_command` (or during `start_command` when it is unsuccessful). - -The members .in, .out, .err are used to redirect stdin, stdout, -stderr as follows: - -. Specify 0 to request no special redirection. No new file descriptor - is allocated. The child process simply inherits the channel from the - parent. - -. Specify -1 to have a pipe allocated; start_command() replaces -1 - by the pipe FD in the following way: - - .in: Returns the writable pipe end into which the caller writes; - the readable end of the pipe becomes the child's stdin. - - .out, .err: Returns the readable pipe end from which the caller - reads; the writable end of the pipe end becomes child's - stdout/stderr. - - The caller of start_command() must close the so returned FDs - after it has completed reading from/writing to it! - -. Specify a file descriptor > 0 to be used by the child: - - .in: The FD must be readable; it becomes child's stdin. - .out: The FD must be writable; it becomes child's stdout. - .err: The FD must be writable; it becomes child's stderr. - - The specified FD is closed by start_command(), even if it fails to - run the sub-process! - -. Special forms of redirection are available by setting these members - to 1: - - .no_stdin, .no_stdout, .no_stderr: The respective channel is - redirected to /dev/null. - - .stdout_to_stderr: stdout of the child is redirected to its - stderr. This happens after stderr is itself redirected. - So stdout will follow stderr to wherever it is - redirected. - -To modify the environment of the sub-process, specify an array of -string pointers (NULL terminated) in .env: - -. If the string is of the form "VAR=value", i.e. it contains '=' - the variable is added to the child process's environment. - -. If the string does not contain '=', it names an environment - variable that will be removed from the child process's environment. - -If the .env member is NULL, `start_command` will point it at the -.env_array `argv_array` (so you may use one or the other, but not both). -The memory in .env_array will be cleaned up automatically during -`finish_command` (or during `start_command` when it is unsuccessful). - -To specify a new initial working directory for the sub-process, -specify it in the .dir member. - -If the program cannot be found, the functions return -1 and set -errno to ENOENT. Normally, an error message is printed, but if -.silent_exec_failure is set to 1, no message is printed for this -special error condition. - - -* `struct async` - -This describes a function to run asynchronously, whose purpose is -to produce output that the caller reads. - -The caller: - -1. allocates and clears (memset(&asy, 0, sizeof(asy));) a - struct async variable; -2. initializes .proc and .data; -3. calls start_async(); -4. processes communicates with proc through .in and .out; -5. closes .in and .out; -6. calls finish_async(). - -The members .in, .out are used to provide a set of fd's for -communication between the caller and the callee as follows: - -. Specify 0 to have no file descriptor passed. The callee will - receive -1 in the corresponding argument. - -. Specify < 0 to have a pipe allocated; start_async() replaces - with the pipe FD in the following way: - - .in: Returns the writable pipe end into which the caller - writes; the readable end of the pipe becomes the function's - in argument. - - .out: Returns the readable pipe end from which the caller - reads; the writable end of the pipe becomes the function's - out argument. - - The caller of start_async() must close the returned FDs after it - has completed reading from/writing from them. - -. Specify a file descriptor > 0 to be used by the function: - - .in: The FD must be readable; it becomes the function's in. - .out: The FD must be writable; it becomes the function's out. - - The specified FD is closed by start_async(), even if it fails to - run the function. - -The function pointer in .proc has the following signature: - - int proc(int in, int out, void *data); - -. in, out specifies a set of file descriptors to which the function - must read/write the data that it needs/produces. The function - *must* close these descriptors before it returns. A descriptor - may be -1 if the caller did not configure a descriptor for that - direction. - -. data is the value that the caller has specified in the .data member - of struct async. - -. The return value of the function is 0 on success and non-zero - on failure. If the function indicates failure, finish_async() will - report failure as well. - - -There are serious restrictions on what the asynchronous function can do -because this facility is implemented by a thread in the same address -space on most platforms (when pthreads is available), but by a pipe to -a forked process otherwise: - -. It cannot change the program's state (global variables, environment, - etc.) in a way that the caller notices; in other words, .in and .out - are the only communication channels to the caller. - -. It must not change the program's state that the caller of the - facility also uses. diff --git a/third_party/git/Documentation/technical/api-setup.txt b/third_party/git/Documentation/technical/api-setup.txt deleted file mode 100644 index eb1fa9853ef6..000000000000 --- a/third_party/git/Documentation/technical/api-setup.txt +++ /dev/null @@ -1,47 +0,0 @@ -setup API -========= - -Talk about - -* setup_git_directory() -* setup_git_directory_gently() -* is_inside_git_dir() -* is_inside_work_tree() -* setup_work_tree() - -(Dscho) - -Pathspec --------- - -See glossary-context.txt for the syntax of pathspec. In memory, a -pathspec set is represented by "struct pathspec" and is prepared by -parse_pathspec(). This function takes several arguments: - -- magic_mask specifies what features that are NOT supported by the - following code. If a user attempts to use such a feature, - parse_pathspec() can reject it early. - -- flags specifies other things that the caller wants parse_pathspec to - perform. - -- prefix and args come from cmd_* functions - -parse_pathspec() helps catch unsupported features and reject them -politely. At a lower level, different pathspec-related functions may -not support the same set of features. Such pathspec-sensitive -functions are guarded with GUARD_PATHSPEC(), which will die in an -unfriendly way when an unsupported feature is requested. - -The command designers are supposed to make sure that GUARD_PATHSPEC() -never dies. They have to make sure all unsupported features are caught -by parse_pathspec(), not by GUARD_PATHSPEC. grepping GUARD_PATHSPEC() -should give the designers all pathspec-sensitive codepaths and what -features they support. - -A similar process is applied when a new pathspec magic is added. The -designer lifts the GUARD_PATHSPEC restriction in the functions that -support the new magic. At the same time (s)he has to make sure this -new feature will be caught at parse_pathspec() in commands that cannot -handle the new magic in some cases. grepping parse_pathspec() should -help. diff --git a/third_party/git/Documentation/technical/api-sigchain.txt b/third_party/git/Documentation/technical/api-sigchain.txt deleted file mode 100644 index 9e1189ef01df..000000000000 --- a/third_party/git/Documentation/technical/api-sigchain.txt +++ /dev/null @@ -1,41 +0,0 @@ -sigchain API -============ - -Code often wants to set a signal handler to clean up temporary files or -other work-in-progress when we die unexpectedly. For multiple pieces of -code to do this without conflicting, each piece of code must remember -the old value of the handler and restore it either when: - - 1. The work-in-progress is finished, and the handler is no longer - necessary. The handler should revert to the original behavior - (either another handler, SIG_DFL, or SIG_IGN). - - 2. The signal is received. We should then do our cleanup, then chain - to the next handler (or die if it is SIG_DFL). - -Sigchain is a tiny library for keeping a stack of handlers. Your handler -and installation code should look something like: - ------------------------------------------- - void clean_foo_on_signal(int sig) - { - clean_foo(); - sigchain_pop(sig); - raise(sig); - } - - void other_func() - { - sigchain_push_common(clean_foo_on_signal); - mess_up_foo(); - clean_foo(); - } ------------------------------------------- - -Handlers are given the typedef of sigchain_fun. This is the same type -that is given to signal() or sigaction(). It is perfectly reasonable to -push SIG_DFL or SIG_IGN onto the stack. - -You can sigchain_push and sigchain_pop individual signals. For -convenience, sigchain_push_common will push the handler onto the stack -for many common signals. diff --git a/third_party/git/Documentation/technical/api-submodule-config.txt b/third_party/git/Documentation/technical/api-submodule-config.txt deleted file mode 100644 index fb060893931f..000000000000 --- a/third_party/git/Documentation/technical/api-submodule-config.txt +++ /dev/null @@ -1,66 +0,0 @@ -submodule config cache API -========================== - -The submodule config cache API allows to read submodule -configurations/information from specified revisions. Internally -information is lazily read into a cache that is used to avoid -unnecessary parsing of the same .gitmodules files. Lookups can be done by -submodule path or name. - -Usage ------ - -To initialize the cache with configurations from the worktree the caller -typically first calls `gitmodules_config()` to read values from the -worktree .gitmodules and then to overlay the local git config values -`parse_submodule_config_option()` from the config parsing -infrastructure. - -The caller can look up information about submodules by using the -`submodule_from_path()` or `submodule_from_name()` functions. They return -a `struct submodule` which contains the values. The API automatically -initializes and allocates the needed infrastructure on-demand. If the -caller does only want to lookup values from revisions the initialization -can be skipped. - -If the internal cache might grow too big or when the caller is done with -the API, all internally cached values can be freed with submodule_free(). - -Data Structures ---------------- - -`struct submodule`:: - - This structure is used to return the information about one - submodule for a certain revision. It is returned by the lookup - functions. - -Functions ---------- - -`void submodule_free(struct repository *r)`:: - - Use these to free the internally cached values. - -`int parse_submodule_config_option(const char *var, const char *value)`:: - - Can be passed to the config parsing infrastructure to parse - local (worktree) submodule configurations. - -`const struct submodule *submodule_from_path(const unsigned char *treeish_name, const char *path)`:: - - Given a tree-ish in the superproject and a path, return the - submodule that is bound at the path in the named tree. - -`const struct submodule *submodule_from_name(const unsigned char *treeish_name, const char *name)`:: - - The same as above but lookup by name. - -Whenever a submodule configuration is parsed in `parse_submodule_config_option` -via e.g. `gitmodules_config()`, it will overwrite the null_sha1 entry. -So in the normal case, when HEAD:.gitmodules is parsed first and then overlayed -with the repository configuration, the null_sha1 entry contains the local -configuration of a submodule (e.g. consolidated values from local git -configuration and the .gitmodules file in the worktree). - -For an example usage see test-submodule-config.c. diff --git a/third_party/git/Documentation/technical/api-trace.txt b/third_party/git/Documentation/technical/api-trace.txt deleted file mode 100644 index fadb5979c48b..000000000000 --- a/third_party/git/Documentation/technical/api-trace.txt +++ /dev/null @@ -1,140 +0,0 @@ -trace API -========= - -The trace API can be used to print debug messages to stderr or a file. Trace -code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment -variables. - -The trace implementation automatically adds `timestamp file:line ... \n` to -all trace messages. E.g.: - ------------- -23:59:59.123456 git.c:312 trace: built-in: git 'foo' -00:00:00.000001 builtin/foo.c:99 foo: some message ------------- - -Data Structures ---------------- - -`struct trace_key`:: - - Defines a trace key (or category). The default (for API functions that - don't take a key) is `GIT_TRACE`. -+ -E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`: -+ ------------- -static struct trace_key trace_foo = TRACE_KEY_INIT(FOO); - -static void trace_print_foo(const char *message) -{ - trace_printf_key(&trace_foo, "%s", message); -} ------------- -+ -Note: don't use `const` as the trace implementation stores internal state in -the `trace_key` structure. - -Functions ---------- - -`int trace_want(struct trace_key *key)`:: - - Checks whether the trace key is enabled. Used to prevent expensive - string formatting before calling one of the printing APIs. - -`void trace_disable(struct trace_key *key)`:: - - Disables tracing for the specified key, even if the environment - variable was set. - -`void trace_printf(const char *format, ...)`:: -`void trace_printf_key(struct trace_key *key, const char *format, ...)`:: - - Prints a formatted message, similar to printf. - -`void trace_argv_printf(const char **argv, const char *format, ...)``:: - - Prints a formatted message, followed by a quoted list of arguments. - -`void trace_strbuf(struct trace_key *key, const struct strbuf *data)`:: - - Prints the strbuf, without additional formatting (i.e. doesn't - choke on `%` or even `\0`). - -`uint64_t getnanotime(void)`:: - - Returns nanoseconds since the epoch (01/01/1970), typically used - for performance measurements. -+ -Currently there are high precision timer implementations for Linux (using -`clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`). -Other platforms use `gettimeofday` as time source. - -`void trace_performance(uint64_t nanos, const char *format, ...)`:: -`void trace_performance_since(uint64_t start, const char *format, ...)`:: - - Prints the elapsed time (in nanoseconds), or elapsed time since - `start`, followed by a formatted message. Enabled via environment - variable `GIT_TRACE_PERFORMANCE`. Used for manual profiling, e.g.: -+ ------------- -uint64_t start = getnanotime(); -/* code section to measure */ -trace_performance_since(start, "foobar"); ------------- -+ ------------- -uint64_t t = 0; -for (;;) { - /* ignore */ - t -= getnanotime(); - /* code section to measure */ - t += getnanotime(); - /* ignore */ -} -trace_performance(t, "frotz"); ------------- - -Bugs & Caveats --------------- - -GIT_TRACE_* environment variables can be used to tell Git to show -trace output to its standard error stream. Git can often spawn a pager -internally to run its subcommand and send its standard output and -standard error to it. - -Because GIT_TRACE_PERFORMANCE trace is generated only at the very end -of the program with atexit(), which happens after the pager exits, it -would not work well if you send its log to the standard error output -and let Git spawn the pager at the same time. - -As a work around, you can for example use '--no-pager', or set -GIT_TRACE_PERFORMANCE to another file descriptor which is redirected -to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its -absolute path. - -For example instead of the following command which by default may not -print any performance information: - ------------- -GIT_TRACE_PERFORMANCE=2 git log -1 ------------- - -you may want to use: - ------------- -GIT_TRACE_PERFORMANCE=2 git --no-pager log -1 ------------- - -or: - ------------- -GIT_TRACE_PERFORMANCE=3 3>&2 git log -1 ------------- - -or: - ------------- -GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1 ------------- diff --git a/third_party/git/Documentation/technical/api-trace2.txt b/third_party/git/Documentation/technical/api-trace2.txt index 71eb081fed25..6b6085585d56 100644 --- a/third_party/git/Documentation/technical/api-trace2.txt +++ b/third_party/git/Documentation/technical/api-trace2.txt @@ -128,7 +128,7 @@ yields ------------ $ cat ~/log.event -{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"1","exe":"2.20.1.155.g426c96fcdb"} +{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"2","exe":"2.20.1.155.g426c96fcdb"} {"event":"start","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621027Z","file":"common-main.c","line":39,"t_abs":0.001173,"argv":["git","version"]} {"event":"cmd_name","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621122Z","file":"git.c","line":432,"name":"version","hierarchy":"version"} {"event":"exit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621236Z","file":"git.c","line":662,"t_abs":0.001227,"code":0} @@ -142,10 +142,9 @@ system or global config value to one of the following: include::../trace2-target-values.txt[] -If the target already exists and is a directory, the traces will be -written to files (one per process) underneath the given directory. They -will be named according to the last component of the SID (optionally -followed by a counter to avoid filename collisions). +When trace files are written to a target directory, they will be named according +to the last component of the SID (optionally followed by a counter to avoid +filename collisions). == Trace2 API @@ -179,7 +178,7 @@ describe the simplified forms. == Public API -All Trace2 API functions send a messsage to all of the active +All Trace2 API functions send a message to all of the active Trace2 Targets. This section describes the set of available messages. @@ -189,261 +188,36 @@ purposes. === Basic Command Messages These are concerned with the lifetime of the overall git process. - -`void trace2_initialize_clock()`:: - - Initialize the Trace2 start clock and nothing else. This should - be called at the very top of main() to capture the process start - time and reduce startup order dependencies. - -`void trace2_initialize()`:: - - Determines if any Trace2 Targets should be enabled and - initializes the Trace2 facility. This includes setting up the - Trace2 thread local storage (TLS). -+ -This function emits a "version" message containing the version of git -and the Trace2 protocol. -+ -This function should be called from `main()` as early as possible in -the life of the process after essential process initialization. - -`int trace2_is_enabled()`:: - - Returns 1 if Trace2 is enabled (at least one target is - active). - -`void trace2_cmd_start(int argc, const char **argv)`:: - - Emits a "start" message containing the process command line - arguments. - -`int trace2_cmd_exit(int exit_code)`:: - - Emits an "exit" message containing the process exit-code and - elapsed time. -+ -Returns the exit-code. - -`void trace2_cmd_error(const char *fmt, va_list ap)`:: - - Emits an "error" message containing a formatted error message. - -`void trace2_cmd_path(const char *pathname)`:: - - Emits a "cmd_path" message with the full pathname of the - current process. +e.g: `void trace2_initialize_clock()`, `void trace2_initialize()`, +`int trace2_is_enabled()`, `void trace2_cmd_start(int argc, const char **argv)`. === Command Detail Messages These are concerned with describing the specific Git command after the command line, config, and environment are inspected. - -`void trace2_cmd_name(const char *name)`:: - - Emits a "cmd_name" message with the canonical name of the - command, for example "status" or "checkout". - -`void trace2_cmd_mode(const char *mode)`:: - - Emits a "cmd_mode" message with a qualifier name to further - describe the current git command. -+ -This message is intended to be used with git commands having multiple -major modes. For example, a "checkout" command can checkout a new -branch or it can checkout a single file, so the checkout code could -emit a cmd_mode message of "branch" or "file". - -`void trace2_cmd_alias(const char *alias, const char **argv_expansion)`:: - - Emits an "alias" message containing the alias used and the - argument expansion. - -`void trace2_def_param(const char *parameter, const char *value)`:: - - Emits a "def_param" message containing a key/value pair. -+ -This message is intended to report some global aspect of the current -command, such as a configuration setting or command line switch that -significantly affects program performance or behavior, such as -`core.abbrev`, `status.showUntrackedFiles`, or `--no-ahead-behind`. - -`void trace2_cmd_list_config()`:: - - Emits a "def_param" messages for "important" configuration - settings. -+ -The environment variable `GIT_TRACE2_CONFIG_PARAMS` or the `trace2.configParams` -config value can be set to a -list of patterns of important configuration settings, for example: -`core.*,remote.*.url`. This function will iterate over all config -settings and emit a "def_param" message for each match. - -`void trace2_cmd_set_config(const char *key, const char *value)`:: - - Emits a "def_param" message for a new or updated key/value - pair IF `key` is considered important. -+ -This is used to hook into `git_config_set()` and catch any -configuration changes and update a value previously reported by -`trace2_cmd_list_config()`. - -`void trace2_def_repo(struct repository *repo)`:: - - Registers a repository with the Trace2 layer. Assigns a - unique "repo-id" to `repo->trace2_repo_id`. -+ -Emits a "worktree" messages containing the repo-id and the worktree -pathname. -+ -Region and data messages (described later) may refer to this repo-id. -+ -The main/top-level repository will have repo-id value 1 (aka "r1"). -+ -The repo-id field is in anticipation of future in-proc submodule -repositories. +e.g: `void trace2_cmd_name(const char *name)`, +`void trace2_cmd_mode(const char *mode)`. === Child Process Messages These are concerned with the various spawned child processes, including shell scripts, git commands, editors, pagers, and hooks. -`void trace2_child_start(struct child_process *cmd)`:: - - Emits a "child_start" message containing the "child-id", - "child-argv", and "child-classification". -+ -Before calling this, set `cmd->trace2_child_class` to a name -describing the type of child process, for example "editor". -+ -This function assigns a unique "child-id" to `cmd->trace2_child_id`. -This field is used later during the "child_exit" message to associate -it with the "child_start" message. -+ -This function should be called before spawning the child process. - -`void trace2_child_exit(struct child_proess *cmd, int child_exit_code)`:: - - Emits a "child_exit" message containing the "child-id", - the child's elapsed time and exit-code. -+ -The reported elapsed time includes the process creation overhead and -time spend waiting for it to exit, so it may be slightly longer than -the time reported by the child itself. -+ -This function should be called after reaping the child process. - -`int trace2_exec(const char *exe, const char **argv)`:: - - Emits a "exec" message containing the "exec-id" and the - argv of the new process. -+ -This function should be called before calling one of the `exec()` -variants, such as `execvp()`. -+ -This function returns a unique "exec-id". This value is used later -if the exec() fails and a "exec-result" message is necessary. - -`void trace2_exec_result(int exec_id, int error_code)`:: - - Emits a "exec_result" message containing the "exec-id" - and the error code. -+ -On Unix-based systems, `exec()` does not return if successful. -This message is used to indicate that the `exec()` failed and -that the current program is continuing. +e.g: `void trace2_child_start(struct child_process *cmd)`. === Git Thread Messages These messages are concerned with Git thread usage. -`void trace2_thread_start(const char *thread_name)`:: - - Emits a "thread_start" message. -+ -The `thread_name` field should be a descriptive name, such as the -unique name of the thread-proc. A unique "thread-id" will be added -to the name to uniquely identify thread instances. -+ -Region and data messages (described later) may refer to this thread -name. -+ -This function must be called by the thread-proc of the new thread -(so that TLS data is properly initialized) and not by the caller -of `pthread_create()`. - -`void trace2_thread_exit()`:: - - Emits a "thread_exit" message containing the thread name - and the thread elapsed time. -+ -This function must be called by the thread-proc before it returns -(so that the coorect TLS data is used and cleaned up. It should -not be called by the caller of `pthread_join()`. +e.g: `void trace2_thread_start(const char *thread_name)`. === Region and Data Messages These are concerned with recording performance data -over regions or spans of code. - -`void trace2_region_enter(const char *category, const char *label, const struct repository *repo)`:: - -`void trace2_region_enter_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`:: - -`void trace2_region_enter_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`:: - - Emits a thread-relative "region_enter" message with optional - printf string. -+ -This function pushes a new region nesting stack level on the current -thread and starts a clock for the new stack frame. -+ -The `category` field is an arbitrary category name used to classify -regions by feature area, such as "status" or "index". At this time -it is only just printed along with the rest of the message. It may -be used in the future to filter messages. -+ -The `label` field is an arbitrary label used to describe the activity -being started, such as "read_recursive" or "do_read_index". -+ -The `repo` field, if set, will be used to get the "repo-id", so that -recursive oerations can be attributed to the correct repository. - -`void trace2_region_leave(const char *category, const char *label, const struct repository *repo)`:: - -`void trace2_region_leave_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`:: - -`void trace2_region_leave_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`:: - - Emits a thread-relative "region_leave" message with optional - printf string. -+ -This function pops the region nesting stack on the current thread -and reports the elapsed time of the stack frame. -+ -The `category`, `label`, and `repo` fields are the same as above. -The `category` and `label` do not need to match the correpsonding -"region_enter" message, but it makes the data stream easier to -understand. - -`void trace2_data_string(const char *category, const struct repository *repo, const char *key, const char * value)`:: - -`void trace2_data_intmax(const char *category, const struct repository *repo, const char *key, intmax value)`:: - -`void trace2_data_json(const char *category, const struct repository *repo, const char *key, const struct json_writer *jw)`:: +over regions or spans of code. e.g: +`void trace2_region_enter(const char *category, const char *label, const struct repository *repo)`. - Emits a region- and thread-relative "data" or "data_json" message. -+ -This is a key/value pair message containing information about the -current thread, region stack, and repository. This could be used -to print the number of files in a directory during a multi-threaded -recursive tree walk. - -`void trace2_printf(const char *fmt, ...)`:: - -`void trace2_printf_va(const char *fmt, va_list ap)`:: - - Emits a region- and thread-relative "printf" message. +Refer to trace2.h for details about all trace2 functions. == Trace2 Target Formats @@ -605,17 +379,35 @@ only present on the "start" and "atexit" events. ==== Event-Specific Key/Value Pairs `"version"`:: - This event gives the version of the executable and the EVENT format. + This event gives the version of the executable and the EVENT format. It + should always be the first event in a trace session. The EVENT format + version will be incremented if new event types are added, if existing + fields are removed, or if there are significant changes in + interpretation of existing events or fields. Smaller changes, such as + adding a new field to an existing event, will not require an increment + to the EVENT format version. + ------------ { "event":"version", ... - "evt":"1", # EVENT format version + "evt":"2", # EVENT format version "exe":"2.20.1.155.g426c96fcdb" # git version } ------------ +`"discard"`:: + This event is written to the git-trace2-discard sentinel file if there + are too many files in the target trace directory (see the + trace2.maxFiles config option). ++ +------------ +{ + "event":"discard", + ... +} +------------ + `"start"`:: This event contains the complete argv received by main(). + @@ -799,7 +591,7 @@ with "?". Note that the session-id of the child process is not available to the current/spawning process, so the child's PID is reported here as a hint for post-processing. (But it is only a hint because the child -proces may be a shell script which doesn't have a session-id.) +process may be a shell script which doesn't have a session-id.) + Note that the `t_rel` field contains the observed run time in seconds for the child process (starting before the fork/exec/spawn and @@ -864,7 +656,8 @@ The "exec_id" field is a command-unique id and is only useful if the ------------ `"def_param"`:: - This event is generated to log a global parameter. + This event is generated to log a global parameter, such as a config + setting, command-line flag, or environment variable. + ------------ { @@ -1159,7 +952,7 @@ d0 | main | atexit | | 0.028809 | | + Regions may be nested. This causes messages to be indented in the PERF target, for example. -Elapsed times are relative to the start of the correpsonding nesting +Elapsed times are relative to the start of the corresponding nesting level as expected. For example, if we add region message to: + ---------------- @@ -1354,7 +1147,7 @@ d0 | main | atexit | | 0.030027 | | In this example, the preload region took 0.009122 seconds. The 7 threads took between 0.006069 and 0.008947 seconds to work on their portion of the index. Thread "th01" worked on 508 items at offset 0. Thread "th02" -worked on 508 items at offset 2032. Thread "th04" worked on 508 itemts +worked on 508 items at offset 2032. Thread "th04" worked on 508 items at offset 508. + This example also shows that thread names are assigned in a racy manner diff --git a/third_party/git/Documentation/technical/api-tree-walking.txt b/third_party/git/Documentation/technical/api-tree-walking.txt deleted file mode 100644 index bde18622a874..000000000000 --- a/third_party/git/Documentation/technical/api-tree-walking.txt +++ /dev/null @@ -1,147 +0,0 @@ -tree walking API -================ - -The tree walking API is used to traverse and inspect trees. - -Data Structures ---------------- - -`struct name_entry`:: - - An entry in a tree. Each entry has a sha1 identifier, pathname, and - mode. - -`struct tree_desc`:: - - A semi-opaque data structure used to maintain the current state of the - walk. -+ -* `buffer` is a pointer into the memory representation of the tree. It always -points at the current entry being visited. - -* `size` counts the number of bytes left in the `buffer`. - -* `entry` points to the current entry being visited. - -`struct traverse_info`:: - - A structure used to maintain the state of a traversal. -+ -* `prev` points to the traverse_info which was used to descend into the -current tree. If this is the top-level tree `prev` will point to -a dummy traverse_info. - -* `name` is the entry for the current tree (if the tree is a subtree). - -* `pathlen` is the length of the full path for the current tree. - -* `conflicts` can be used by callbacks to maintain directory-file conflicts. - -* `fn` is a callback called for each entry in the tree. See Traversing for more -information. - -* `data` can be anything the `fn` callback would want to use. - -* `show_all_errors` tells whether to stop at the first error or not. - -Initializing ------------- - -`init_tree_desc`:: - - Initialize a `tree_desc` and decode its first entry. The buffer and - size parameters are assumed to be the same as the buffer and size - members of `struct tree`. - -`fill_tree_descriptor`:: - - Initialize a `tree_desc` and decode its first entry given the - object ID of a tree. Returns the `buffer` member if the latter - is a valid tree identifier and NULL otherwise. - -`setup_traverse_info`:: - - Initialize a `traverse_info` given the pathname of the tree to start - traversing from. The `base` argument is assumed to be the `path` - member of the `name_entry` being recursed into unless the tree is a - top-level tree in which case the empty string ("") is used. - -Walking -------- - -`tree_entry`:: - - Visit the next entry in a tree. Returns 1 when there are more entries - left to visit and 0 when all entries have been visited. This is - commonly used in the test of a while loop. - -`tree_entry_len`:: - - Calculate the length of a tree entry's pathname. This utilizes the - memory structure of a tree entry to avoid the overhead of using a - generic strlen(). - -`update_tree_entry`:: - - Walk to the next entry in a tree. This is commonly used in conjunction - with `tree_entry_extract` to inspect the current entry. - -`tree_entry_extract`:: - - Decode the entry currently being visited (the one pointed to by - `tree_desc's` `entry` member) and return the sha1 of the entry. The - `pathp` and `modep` arguments are set to the entry's pathname and mode - respectively. - -`get_tree_entry`:: - - Find an entry in a tree given a pathname and the sha1 of a tree to - search. Returns 0 if the entry is found and -1 otherwise. The third - and fourth parameters are set to the entry's sha1 and mode - respectively. - -Traversing ----------- - -`traverse_trees`:: - - Traverse `n` number of trees in parallel. The `fn` callback member of - `traverse_info` is called once for each tree entry. - -`traverse_callback_t`:: - The arguments passed to the traverse callback are as follows: -+ -* `n` counts the number of trees being traversed. - -* `mask` has its nth bit set if something exists in the nth entry. - -* `dirmask` has its nth bit set if the nth tree's entry is a directory. - -* `entry` is an array of size `n` where the nth entry is from the nth tree. - -* `info` maintains the state of the traversal. - -+ -Returning a negative value will terminate the traversal. Otherwise the -return value is treated as an update mask. If the nth bit is set the nth tree -will be updated and if the bit is not set the nth tree entry will be the -same in the next callback invocation. - -`make_traverse_path`:: - - Generate the full pathname of a tree entry based from the root of the - traversal. For example, if the traversal has recursed into another - tree named "bar" the pathname of an entry "baz" in the "bar" - tree would be "bar/baz". - -`traverse_path_len`:: - - Calculate the length of a pathname returned by `make_traverse_path`. - This utilizes the memory structure of a tree entry to avoid the - overhead of using a generic strlen(). - -Authors -------- - -Written by Junio C Hamano <gitster@pobox.com> and Linus Torvalds -<torvalds@linux-foundation.org> diff --git a/third_party/git/Documentation/technical/api-xdiff-interface.txt b/third_party/git/Documentation/technical/api-xdiff-interface.txt deleted file mode 100644 index 6296ecad1d65..000000000000 --- a/third_party/git/Documentation/technical/api-xdiff-interface.txt +++ /dev/null @@ -1,7 +0,0 @@ -xdiff interface API -=================== - -Talk about our calling convention to xdiff library, including -xdiff_emit_consume_fn. - -(Dscho, JC) diff --git a/third_party/git/Documentation/technical/bundle-format.txt b/third_party/git/Documentation/technical/bundle-format.txt new file mode 100644 index 000000000000..bac558d049a3 --- /dev/null +++ b/third_party/git/Documentation/technical/bundle-format.txt @@ -0,0 +1,76 @@ += Git bundle v2 format + +The Git bundle format is a format that represents both refs and Git objects. + +== Format + +We will use ABNF notation to define the Git bundle format. See +protocol-common.txt for the details. + +A v2 bundle looks like this: + +---- +bundle = signature *prerequisite *reference LF pack +signature = "# v2 git bundle" LF + +prerequisite = "-" obj-id SP comment LF +comment = *CHAR +reference = obj-id SP refname LF + +pack = ... ; packfile +---- + +A v3 bundle looks like this: + +---- +bundle = signature *capability *prerequisite *reference LF pack +signature = "# v3 git bundle" LF + +capability = "@" key ["=" value] LF +prerequisite = "-" obj-id SP comment LF +comment = *CHAR +reference = obj-id SP refname LF +key = 1*(ALPHA / DIGIT / "-") +value = *(%01-09 / %0b-FF) + +pack = ... ; packfile +---- + +== Semantics + +A Git bundle consists of several parts. + +* "Capabilities", which are only in the v3 format, indicate functionality that + the bundle requires to be read properly. + +* "Prerequisites" lists the objects that are NOT included in the bundle and the + reader of the bundle MUST already have, in order to use the data in the + bundle. The objects stored in the bundle may refer to prerequisite objects and + anything reachable from them (e.g. a tree object in the bundle can reference + a blob that is reachable from a prerequisite) and/or expressed as a delta + against prerequisite objects. + +* "References" record the tips of the history graph, iow, what the reader of the + bundle CAN "git fetch" from it. + +* "Pack" is the pack data stream "git fetch" would send, if you fetch from a + repository that has the references recorded in the "References" above into a + repository that has references pointing at the objects listed in + "Prerequisites" above. + +In the bundle format, there can be a comment following a prerequisite obj-id. +This is a comment and it has no specific meaning. The writer of the bundle MAY +put any string here. The reader of the bundle MUST ignore the comment. + +=== Note on the shallow clone and a Git bundle + +Note that the prerequisites does not represent a shallow-clone boundary. The +semantics of the prerequisites and the shallow-clone boundaries are different, +and the Git bundle v2 format cannot represent a shallow clone repository. + +== Capabilities + +Because there is no opportunity for negotiation, unknown capabilities cause 'git +bundle' to abort. The only known capability is `object-format`, which specifies +the hash algorithm in use, and can take the same values as the +`extensions.objectFormat` configuration value. diff --git a/third_party/git/Documentation/technical/commit-graph-format.txt b/third_party/git/Documentation/technical/commit-graph-format.txt index a4f17441aed3..b3b58880b926 100644 --- a/third_party/git/Documentation/technical/commit-graph-format.txt +++ b/third_party/git/Documentation/technical/commit-graph-format.txt @@ -17,6 +17,9 @@ metadata, including: - The parents of the commit, stored using positional references within the graph file. +- The Bloom filter of the commit carrying the paths that were changed between + the commit and its first parent, if requested. + These positional references are stored as unsigned 32-bit integers corresponding to the array position within the list of commit OIDs. Due to some special constants we use to track parents, we can store at most @@ -29,7 +32,7 @@ the body into "chunks" and provide a binary lookup table at the beginning of the body. The header includes certain values, such as number of chunks and hash type. -All 4-byte numbers are in network order. +All multi-byte numbers are in network byte order. HEADER: @@ -39,8 +42,13 @@ HEADER: 1-byte version number: Currently, the only valid version is 1. - 1-byte Hash Version (1 = SHA-1) - We infer the hash length (H) from this value. + 1-byte Hash Version + We infer the hash length (H) from this value: + 1 => SHA-1 + 2 => SHA-256 + If the hash type does not match the repository's hash algorithm, the + commit-graph file should be ignored with a warning presented to the + user. 1-byte number (C) of "chunks" @@ -74,7 +82,7 @@ CHUNK DATA: Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes) * The first H bytes are for the OID of the root tree. * The next 8 bytes are for the positions of the first two parents - of the ith commit. Stores value 0x7000000 if no parent in that + of the ith commit. Stores value 0x70000000 if no parent in that position. If there are more than two parents, the second value has its most-significant bit on and the other bits store an array position into the Extra Edge List chunk. @@ -93,6 +101,33 @@ CHUNK DATA: positions for the parents until reaching a value with the most-significant bit on. The other bits correspond to the position of the last parent. + Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional] + * The ith entry, BIDX[i], stores the number of bytes in all Bloom filters + from commit 0 to commit i (inclusive) in lexicographic order. The Bloom + filter for the i-th commit spans from BIDX[i-1] to BIDX[i] (plus header + length), where BIDX[-1] is 0. + * The BIDX chunk is ignored if the BDAT chunk is not present. + + Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional] + * It starts with header consisting of three unsigned 32-bit integers: + - Version of the hash algorithm being used. We currently only support + value 1 which corresponds to the 32-bit version of the murmur3 hash + implemented exactly as described in + https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double + hashing technique using seed values 0x293ae76f and 0x7e646e2 as + described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters + in Probabilistic Verification" + - The number of times a path is hashed and hence the number of bit positions + that cumulatively determine whether a file is present in the commit. + - The minimum number of bits 'b' per entry in the Bloom filter. If the filter + contains 'n' entries, then the filter size is the minimum number of 64-bit + words that contain n*b bits. + * The rest of the chunk is the concatenation of all the computed Bloom + filters for the commits in lexicographic order. + * Note: Commits with no changes or more than 512 changes have Bloom filters + of length one, with either all bits set to zero or one respectively. + * The BDAT chunk is present if and only if BIDX is present. + Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional] This list of H-byte hashes describe a set of B commit-graph files that form a commit-graph chain. The graph position for the ith commit in this diff --git a/third_party/git/Documentation/technical/commit-graph.txt b/third_party/git/Documentation/technical/commit-graph.txt index 729fbcb32f87..f14a7659aa87 100644 --- a/third_party/git/Documentation/technical/commit-graph.txt +++ b/third_party/git/Documentation/technical/commit-graph.txt @@ -22,11 +22,11 @@ as "commit-graph" either in the .git/objects/info directory or in the info directory of an alternate. The commit-graph file stores the commit graph structure along with some -extra metadata to speed up graph walks. By listing commit OIDs in lexi- -cographic order, we can identify an integer position for each commit and -refer to the parents of a commit using those integer positions. We use -binary search to find initial commits and then use the integer positions -for fast lookups during the walk. +extra metadata to speed up graph walks. By listing commit OIDs in +lexicographic order, we can identify an integer position for each commit +and refer to the parents of a commit using those integer positions. We +use binary search to find initial commits and then use the integer +positions for fast lookups during the walk. A consumer may load the following info for a commit from the graph: @@ -85,7 +85,7 @@ have generation number represented by the macro GENERATION_NUMBER_ZERO = 0. Since the commit-graph file is closed under reachability, we can guarantee the following weaker condition on all commits: - If A and B are commits with generation numbers N amd M, respectively, + If A and B are commits with generation numbers N and M, respectively, and N < M, then A cannot reach B. Note how the strict inequality differs from the inequality when we have @@ -210,12 +210,12 @@ file. +---------------------+ | | +-----------------------+ +---------------------+ - | graph-{hash2} |->| | + | graph-{hash2} |->| | +-----------------------+ +---------------------+ | | | +-----------------------+ +---------------------+ | | | | - | graph-{hash1} |->| | + | graph-{hash1} |->| | | | | | +-----------------------+ +---------------------+ | tmp_graphXXX @@ -223,7 +223,7 @@ file. | | | | | | - | graph-{hash0} | + | graph-{hash0} | | | | | | | @@ -323,14 +323,14 @@ Related Links [0] https://bugs.chromium.org/p/git/issues/detail?id=8 Chromium work item for: Serialized Commit Graph -[1] https://public-inbox.org/git/20110713070517.GC18566@sigill.intra.peff.net/ +[1] https://lore.kernel.org/git/20110713070517.GC18566@sigill.intra.peff.net/ An abandoned patch that introduced generation numbers. -[2] https://public-inbox.org/git/20170908033403.q7e6dj7benasrjes@sigill.intra.peff.net/ +[2] https://lore.kernel.org/git/20170908033403.q7e6dj7benasrjes@sigill.intra.peff.net/ Discussion about generation numbers on commits and how they interact with fsck. -[3] https://public-inbox.org/git/20170908034739.4op3w4f2ma5s65ku@sigill.intra.peff.net/ +[3] https://lore.kernel.org/git/20170908034739.4op3w4f2ma5s65ku@sigill.intra.peff.net/ More discussion about generation numbers and not storing them inside commit objects. A valuable quote: @@ -342,9 +342,9 @@ Related Links commit objects (i.e., packv4 or something like the "metapacks" I proposed a few years ago)." -[4] https://public-inbox.org/git/20180108154822.54829-1-git@jeffhostetler.com/T/#u +[4] https://lore.kernel.org/git/20180108154822.54829-1-git@jeffhostetler.com/T/#u A patch to remove the ahead-behind calculation from 'status'. -[5] https://public-inbox.org/git/f27db281-abad-5043-6d71-cbb083b1c877@gmail.com/ +[5] https://lore.kernel.org/git/f27db281-abad-5043-6d71-cbb083b1c877@gmail.com/ A discussion of a "two-dimensional graph position" that can allow reading multiple commit-graph chains at the same time. diff --git a/third_party/git/Documentation/technical/hash-function-transition.txt b/third_party/git/Documentation/technical/hash-function-transition.txt index 2ae8fa470ada..6fd20ebbc254 100644 --- a/third_party/git/Documentation/technical/hash-function-transition.txt +++ b/third_party/git/Documentation/technical/hash-function-transition.txt @@ -531,7 +531,7 @@ Until Git protocol gains SHA-256 support, using SHA-256 based storage on public-facing Git servers is strongly discouraged. Once Git protocol gains SHA-256 support, SHA-256 based servers are likely not to support SHA-1 compatibility, to avoid what may be a very expensive -hash reencode during clone and to encourage peers to modernize. +hash re-encode during clone and to encourage peers to modernize. The design described here allows fetches by SHA-1 clients of a personal SHA-256 repository because it's not much more difficult than @@ -602,7 +602,7 @@ git --output-format=sha1 log abac87a^{sha1}..f787cac^{sha256} Choice of Hash -------------- -In early 2005, around the time that Git was written, Xiaoyun Wang, +In early 2005, around the time that Git was written, Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu announced an attack finding SHA-1 collisions in 2^69 operations. In August they published details. Luckily, no practical demonstrations of a collision in full SHA-1 were @@ -650,7 +650,6 @@ Some initial steps can be implemented independently of one another: The first user-visible change is the introduction of the objectFormat extension (without compatObjectFormat). This requires: -- implementing the loose-object-idx - teaching fsck about this mode of operation - using the hash function API (vtable) when computing object names - signing objects and verifying signatures @@ -658,6 +657,7 @@ extension (without compatObjectFormat). This requires: repository Next comes introduction of compatObjectFormat: +- implementing the loose-object-idx - translating object names between object formats - translating object content between object formats - generating and verifying signatures in the compat format @@ -730,7 +730,7 @@ adoption. Using hash functions in parallel ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -(e.g. https://public-inbox.org/git/22708.8913.864049.452252@chiark.greenend.org.uk/ ) +(e.g. https://lore.kernel.org/git/22708.8913.864049.452252@chiark.greenend.org.uk/ ) Objects newly created would be addressed by the new hash, but inside such an object (e.g. commit) it is still possible to address objects using the old hash function. @@ -783,7 +783,7 @@ bmwill@google.com, jonathantanmy@google.com, jrnieder@gmail.com, sbeller@google.com Initial version sent to -http://public-inbox.org/git/20170304011251.GA26789@aiede.mtv.corp.google.com +http://lore.kernel.org/git/20170304011251.GA26789@aiede.mtv.corp.google.com 2017-03-03 jrnieder@gmail.com Incorporated suggestions from jonathantanmy and sbeller: @@ -820,8 +820,8 @@ Later history: edits. This document history is no longer being maintained as it would now be superfluous to the commit log -[1] http://public-inbox.org/git/CA+55aFzJtejiCjV0e43+9oR3QuJK2PiFiLQemytoLpyJWe6P9w@mail.gmail.com/ -[2] http://public-inbox.org/git/CA+55aFz+gkAsDZ24zmePQuEs1XPS9BP_s8O7Q4wQ7LV7X5-oDA@mail.gmail.com/ -[3] http://public-inbox.org/git/20170306084353.nrns455dvkdsfgo5@sigill.intra.peff.net/ -[4] http://public-inbox.org/git/20170304224936.rqqtkdvfjgyezsht@genre.crustytoothpaste.net -[5] https://public-inbox.org/git/CAJo=hJtoX9=AyLHHpUJS7fueV9ciZ_MNpnEPHUz8Whui6g9F0A@mail.gmail.com/ +[1] http://lore.kernel.org/git/CA+55aFzJtejiCjV0e43+9oR3QuJK2PiFiLQemytoLpyJWe6P9w@mail.gmail.com/ +[2] http://lore.kernel.org/git/CA+55aFz+gkAsDZ24zmePQuEs1XPS9BP_s8O7Q4wQ7LV7X5-oDA@mail.gmail.com/ +[3] http://lore.kernel.org/git/20170306084353.nrns455dvkdsfgo5@sigill.intra.peff.net/ +[4] http://lore.kernel.org/git/20170304224936.rqqtkdvfjgyezsht@genre.crustytoothpaste.net +[5] https://lore.kernel.org/git/CAJo=hJtoX9=AyLHHpUJS7fueV9ciZ_MNpnEPHUz8Whui6g9F0A@mail.gmail.com/ diff --git a/third_party/git/Documentation/technical/http-protocol.txt b/third_party/git/Documentation/technical/http-protocol.txt index 9c5b6f0facbf..96d89ea9b226 100644 --- a/third_party/git/Documentation/technical/http-protocol.txt +++ b/third_party/git/Documentation/technical/http-protocol.txt @@ -216,7 +216,7 @@ smart server reply: S: 001e# service=git-upload-pack\n S: 0000 S: 004895dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint\0multi_ack\n - S: 0042d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master\n + S: 003fd049f6c27a2244e12041955e262a404c7faba355 refs/heads/master\n S: 003c2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0\n S: 003fa3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{}\n S: 0000 @@ -401,8 +401,9 @@ at all in the request stream: The stream is terminated by a pkt-line flush (`0000`). A single "want" or "have" command MUST have one hex formatted -SHA-1 as its value. Multiple SHA-1s MUST be sent by sending -multiple commands. +object name as its value. Multiple object names MUST be sent by sending +multiple commands. Object names MUST be given using the object format +negotiated through the `object-format` capability (default SHA-1). The `have` list is created by popping the first 32 commits from `c_pending`. Less can be supplied if `c_pending` empties. diff --git a/third_party/git/Documentation/technical/index-format.txt b/third_party/git/Documentation/technical/index-format.txt index 7c4d67aa6a7f..f9a3644711b9 100644 --- a/third_party/git/Documentation/technical/index-format.txt +++ b/third_party/git/Documentation/technical/index-format.txt @@ -3,8 +3,11 @@ Git index format == The Git index file has the following format - All binary numbers are in network byte order. Version 2 is described - here unless stated otherwise. + All binary numbers are in network byte order. + In a repository using the traditional SHA-1, checksums and object IDs + (object names) mentioned below are all computed using SHA-1. Similarly, + in SHA-256 repositories, these values are computed using SHA-256. + Version 2 is described here unless stated otherwise. - A 12-byte header consisting of @@ -32,8 +35,7 @@ Git index format Extension data - - 160-bit SHA-1 over the content of the index file before this - checksum. + - Hash checksum over the content of the index file before this checksum. == Index entry @@ -80,7 +82,7 @@ Git index format 32-bit file size This is the on-disk size from stat(2), truncated to 32-bit. - 160-bit SHA-1 for the represented object + Object name for the represented object A 16-bit 'flags' field split into (high to low bits) @@ -160,8 +162,8 @@ Git index format - A newline (ASCII 10); and - - 160-bit object name for the object that would result from writing - this span of index as a tree. + - Object name for the object that would result from writing this span + of index as a tree. An entry can be in an invalidated state and is represented by having a negative number in the entry_count field. In this case, there is no @@ -198,7 +200,7 @@ Git index format stage 1 to 3 (a missing stage is represented by "0" in this field); and - - At most three 160-bit object names of the entry in stages from 1 to 3 + - At most three object names of the entry in stages from 1 to 3 (nothing is written for a missing stage). === Split index @@ -211,8 +213,8 @@ Git index format The extension consists of: - - 160-bit SHA-1 of the shared index file. The shared index file path - is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the + - Hash of the shared index file. The shared index file path + is $GIT_DIR/sharedindex.<hash>. If all bits are zero, the index does not require a shared index file. - An ewah-encoded delete bitmap, each bit represents an entry in the @@ -253,10 +255,10 @@ Git index format - 32-bit dir_flags (see struct dir_struct) - - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file + - Hash of $GIT_DIR/info/exclude. A null hash means the file does not exist. - - 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does + - Hash of core.excludesfile. A null hash means the file does not exist. - NUL-terminated string of per-dir exclude file name. This usually @@ -285,13 +287,13 @@ The remaining data of each directory block is grouped by type: - An ewah bitmap, the n-th bit records "check-only" bit of read_directory_recursive() for the n-th directory. - - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data + - An ewah bitmap, the n-th bit indicates whether hash and stat data is valid for the n-th directory and exists in the next data. - An array of stat data. The n-th data corresponds with the n-th "one" bit in the previous ewah bitmap. - - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit + - An array of hashes. The n-th hash corresponds with the n-th "one" bit in the previous ewah bitmap. - One NUL. @@ -318,7 +320,7 @@ The remaining data of each directory block is grouped by type: == End of Index Entry The End of Index Entry (EOIE) is used to locate the end of the variable - length index entries and the begining of the extensions. Code can take + length index entries and the beginning of the extensions. Code can take advantage of this to quickly locate the index extensions without having to parse through all of the index entries. @@ -330,12 +332,12 @@ The remaining data of each directory block is grouped by type: - 32-bit offset to the end of the index entries - - 160-bit SHA-1 over the extension types and their sizes (but not + - Hash over the extension types and their sizes (but not their contents). E.g. if we have "TREE" extension that is N-bytes long, "REUC" extension that is M-bytes long, followed by "EOIE", then the hash would be: - SHA-1("TREE" + <binary representation of N> + + Hash("TREE" + <binary representation of N> + "REUC" + <binary representation of M>) == Index Entry Offset Table @@ -351,7 +353,7 @@ The remaining data of each directory block is grouped by type: - A number of index offset entries each consisting of: - - 32-bit offset from the begining of the file to the first cache entry + - 32-bit offset from the beginning of the file to the first cache entry in this block of entries. - 32-bit count of cache entries in this block diff --git a/third_party/git/Documentation/technical/multi-pack-index.txt b/third_party/git/Documentation/technical/multi-pack-index.txt index d7e57639f70d..4e7631437a58 100644 --- a/third_party/git/Documentation/technical/multi-pack-index.txt +++ b/third_party/git/Documentation/technical/multi-pack-index.txt @@ -36,7 +36,7 @@ Design Details directory of an alternate. It refers only to packfiles in that same directory. -- The pack.multiIndex config setting must be on to consume MIDX files. +- The core.multiPackIndex config setting must be on to consume MIDX files. - The file format includes parameters for the object ID hash function, so a future change of hash algorithm does not require @@ -102,8 +102,8 @@ Related Links [0] https://bugs.chromium.org/p/git/issues/detail?id=6 Chromium work item for: Multi-Pack Index (MIDX) -[1] https://public-inbox.org/git/20180107181459.222909-1-dstolee@microsoft.com/ +[1] https://lore.kernel.org/git/20180107181459.222909-1-dstolee@microsoft.com/ An earlier RFC for the multi-pack-index feature -[2] https://public-inbox.org/git/alpine.DEB.2.20.1803091557510.23109@alexmv-linux/ +[2] https://lore.kernel.org/git/alpine.DEB.2.20.1803091557510.23109@alexmv-linux/ Git Merge 2018 Contributor's summit notes (includes discussion of MIDX) diff --git a/third_party/git/Documentation/technical/pack-format.txt b/third_party/git/Documentation/technical/pack-format.txt index cab5bdd2ff0f..f96b2e605f34 100644 --- a/third_party/git/Documentation/technical/pack-format.txt +++ b/third_party/git/Documentation/technical/pack-format.txt @@ -1,6 +1,12 @@ Git pack format =============== +== Checksums and object IDs + +In a repository using the traditional SHA-1, pack checksums, index checksums, +and object IDs (object names) mentioned below are all computed using SHA-1. +Similarly, in SHA-256 repositories, these values are computed using SHA-256. + == pack-*.pack files have the following format: - A header appears at the beginning and consists of the following: @@ -26,7 +32,7 @@ Git pack format (deltified representation) n-byte type and length (3-bit type, (n-1)*7+4-bit length) - 20-byte base object name if OBJ_REF_DELTA or a negative relative + base object name if OBJ_REF_DELTA or a negative relative offset from the delta object's position in the pack if this is an OBJ_OFS_DELTA object compressed delta data @@ -34,7 +40,7 @@ Git pack format Observation: length of each object is encoded in a variable length format and is not constrained to 32-bit or anything. - - The trailer records 20-byte SHA-1 checksum of all of the above. + - The trailer records a pack checksum of all of the above. === Object types @@ -58,8 +64,8 @@ ofs-delta and ref-delta, which is only valid in a pack file. Both ofs-delta and ref-delta store the "delta" to be applied to another object (called 'base object') to reconstruct the object. The -difference between them is, ref-delta directly encodes 20-byte base -object name. If the base object is in the same pack, ofs-delta encodes +difference between them is, ref-delta directly encodes base object +name. If the base object is in the same pack, ofs-delta encodes the offset of the base object in the pack instead. The base object could also be deltified if it's in the same pack. @@ -143,14 +149,14 @@ This is the instruction reserved for future expansion. object is stored in the packfile as the offset from the beginning. - 20-byte object name. + one object name of the appropriate size. - The file is concluded with a trailer: - A copy of the 20-byte SHA-1 checksum at the end of - corresponding packfile. + A copy of the pack checksum at the end of the corresponding + packfile. - 20-byte SHA-1-checksum of all of the above. + Index checksum of all of the above. Pack Idx file: @@ -198,7 +204,7 @@ Pack file entry: <+ If it is not DELTA, then deflated bytes (the size above is the size before compression). If it is REF_DELTA, then - 20-byte base object name SHA-1 (the size above is the + base object name (the size above is the size of the delta data that follows). delta data, deflated. If it is OFS_DELTA, then @@ -227,9 +233,9 @@ Pack file entry: <+ - A 256-entry fan-out table just like v1. - - A table of sorted 20-byte SHA-1 object names. These are - packed together without offset values to reduce the cache - footprint of the binary search for a specific object name. + - A table of sorted object names. These are packed together + without offset values to reduce the cache footprint of the + binary search for a specific object name. - A table of 4-byte CRC32 values of the packed object data. This is new in v2 so compressed data can be copied directly @@ -248,10 +254,10 @@ Pack file entry: <+ - The same trailer as a v1 pack file: - A copy of the 20-byte SHA-1 checksum at the end of + A copy of the pack checksum at the end of corresponding packfile. - 20-byte SHA-1-checksum of all of the above. + Index checksum of all of the above. == multi-pack-index (MIDX) files have the following format: @@ -273,7 +279,12 @@ HEADER: Git only writes or recognizes version 1. 1-byte Object Id Version - Git only writes or recognizes version 1 (SHA1). + We infer the length of object IDs (OIDs) from this value: + 1 => SHA-1 + 2 => SHA-256 + If the hash type does not match the repository's hash algorithm, + the multi-pack-index file should be ignored with a warning + presented to the user. 1-byte number of "chunks" @@ -315,10 +326,11 @@ CHUNK DATA: Stores two 4-byte values for every object. 1: The pack-int-id for the pack storing this object. 2: The offset within the pack. - If all offsets are less than 2^31, then the large offset chunk + If all offsets are less than 2^32, then the large offset chunk will not exist and offsets are stored as in IDX v1. If there is at least one offset value larger than 2^32-1, then - the large offset chunk must exist. If the large offset chunk + the large offset chunk must exist, and offsets larger than + 2^31-1 must be stored in it instead. If the large offset chunk exists and the 31st bit is on, then removing that bit reveals the row in the large offsets containing the 8-byte offset of this object. @@ -328,4 +340,4 @@ CHUNK DATA: TRAILER: - 20-byte SHA1-checksum of the above contents. + Index checksum of the above contents. diff --git a/third_party/git/Documentation/technical/pack-protocol.txt b/third_party/git/Documentation/technical/pack-protocol.txt index c73e72de0e9c..e13a2c064d12 100644 --- a/third_party/git/Documentation/technical/pack-protocol.txt +++ b/third_party/git/Documentation/technical/pack-protocol.txt @@ -96,7 +96,7 @@ Basically what the Git client is doing to connect to an 'upload-pack' process on the server side over the Git protocol is this: $ echo -e -n \ - "0039git-upload-pack /schacon/gitbook.git\0host=example.com\0" | + "003agit-upload-pack /schacon/gitbook.git\0host=example.com\0" | nc -v example.com 9418 @@ -171,9 +171,9 @@ with a version number (if "version=1" is sent as an Extra Parameter), and a listing of each reference it has (all branches and tags) along with the object name that each reference currently points to. - $ echo -e -n "0044git-upload-pack /schacon/gitbook.git\0host=example.com\0\0version=1\0" | + $ echo -e -n "0045git-upload-pack /schacon/gitbook.git\0host=example.com\0\0version=1\0" | nc -v example.com 9418 - 000aversion 1 + 000eversion 1 00887217a7c7e582c46cec22a130adf4b9d7d950fba0 HEAD\0multi_ack thin-pack side-band side-band-64k ofs-delta shallow no-progress include-tag 00441d3fcd5ced445d1abc402225c0b8a1299641f497 refs/heads/integration @@ -503,8 +503,8 @@ The reference discovery phase is done nearly the same way as it is in the fetching protocol. Each reference obj-id and name on the server is sent in packet-line format to the client, followed by a flush-pkt. The only real difference is that the capability listing is different - the only -possible values are 'report-status', 'delete-refs', 'ofs-delta' and -'push-options'. +possible values are 'report-status', 'report-status-v2', 'delete-refs', +'ofs-delta', 'atomic' and 'push-options'. Reference Update Request and Packfile Transfer ---------------------------------------------- @@ -625,7 +625,7 @@ Report Status ------------- After receiving the pack data from the sender, the receiver sends a -report if 'report-status' capability is in effect. +report if 'report-status' or 'report-status-v2' capability is in effect. It is a short listing of what happened in that update. It will first list the status of the packfile unpacking as either 'unpack ok' or 'unpack [error]'. Then it will list the status for each of the references @@ -644,7 +644,42 @@ update was successful, or 'ng [refname] [error]' if the update was not. command-ok = PKT-LINE("ok" SP refname) command-fail = PKT-LINE("ng" SP refname SP error-msg) - error-msg = 1*(OCTECT) ; where not "ok" + error-msg = 1*(OCTET) ; where not "ok" +---- + +The 'report-status-v2' capability extends the protocol by adding new option +lines in order to support reporting of reference rewritten by the +'proc-receive' hook. The 'proc-receive' hook may handle a command for a +pseudo-reference which may create or update one or more references, and each +reference may have different name, different new-oid, and different old-oid. + +---- + report-status-v2 = unpack-status + 1*(command-status-v2) + flush-pkt + + unpack-status = PKT-LINE("unpack" SP unpack-result) + unpack-result = "ok" / error-msg + + command-status-v2 = command-ok-v2 / command-fail + command-ok-v2 = command-ok + *option-line + + command-ok = PKT-LINE("ok" SP refname) + command-fail = PKT-LINE("ng" SP refname SP error-msg) + + error-msg = 1*(OCTET) ; where not "ok" + + option-line = *1(option-refname) + *1(option-old-oid) + *1(option-new-oid) + *1(option-forced-update) + + option-refname = PKT-LINE("option" SP "refname" SP refname) + option-old-oid = PKT-LINE("option" SP "old-oid" SP obj-id) + option-new-oid = PKT-LINE("option" SP "new-oid" SP obj-id) + option-force = PKT-LINE("option" SP "forced-update") + ---- Updates can be unsuccessful for a number of reasons. The reference can have diff --git a/third_party/git/Documentation/technical/packfile-uri.txt b/third_party/git/Documentation/technical/packfile-uri.txt new file mode 100644 index 000000000000..318713abc371 --- /dev/null +++ b/third_party/git/Documentation/technical/packfile-uri.txt @@ -0,0 +1,78 @@ +Packfile URIs +============= + +This feature allows servers to serve part of their packfile response as URIs. +This allows server designs that improve scalability in bandwidth and CPU usage +(for example, by serving some data through a CDN), and (in the future) provides +some measure of resumability to clients. + +This feature is available only in protocol version 2. + +Protocol +-------- + +The server advertises the `packfile-uris` capability. + +If the client then communicates which protocols (HTTPS, etc.) it supports with +a `packfile-uris` argument, the server MAY send a `packfile-uris` section +directly before the `packfile` section (right after `wanted-refs` if it is +sent) containing URIs of any of the given protocols. The URIs point to +packfiles that use only features that the client has declared that it supports +(e.g. ofs-delta and thin-pack). See protocol-v2.txt for the documentation of +this section. + +Clients should then download and index all the given URIs (in addition to +downloading and indexing the packfile given in the `packfile` section of the +response) before performing the connectivity check. + +Server design +------------- + +The server can be trivially made compatible with the proposed protocol by +having it advertise `packfile-uris`, tolerating the client sending +`packfile-uris`, and never sending any `packfile-uris` section. But we should +include some sort of non-trivial implementation in the Minimum Viable Product, +at least so that we can test the client. + +This is the implementation: a feature, marked experimental, that allows the +server to be configured by one or more `uploadpack.blobPackfileUri=<sha1> +<uri>` entries. Whenever the list of objects to be sent is assembled, all such +blobs are excluded, replaced with URIs. The client will download those URIs, +expecting them to each point to packfiles containing single blobs. + +Client design +------------- + +The client has a config variable `fetch.uriprotocols` that determines which +protocols the end user is willing to use. By default, this is empty. + +When the client downloads the given URIs, it should store them with "keep" +files, just like it does with the packfile in the `packfile` section. These +additional "keep" files can only be removed after the refs have been updated - +just like the "keep" file for the packfile in the `packfile` section. + +The division of work (initial fetch + additional URIs) introduces convenient +points for resumption of an interrupted clone - such resumption can be done +after the Minimum Viable Product (see "Future work"). + +Future work +----------- + +The protocol design allows some evolution of the server and client without any +need for protocol changes, so only a small-scoped design is included here to +form the MVP. For example, the following can be done: + + * On the server, more sophisticated means of excluding objects (e.g. by + specifying a commit to represent that commit and all objects that it + references). + * On the client, resumption of clone. If a clone is interrupted, information + could be recorded in the repository's config and a "clone-resume" command + can resume the clone in progress. (Resumption of subsequent fetches is more + difficult because that must deal with the user wanting to use the repository + even after the fetch was interrupted.) + +There are some possible features that will require a change in protocol: + + * Additional HTTP headers (e.g. authentication) + * Byte range support + * Different file formats referenced by URIs (e.g. raw object) diff --git a/third_party/git/Documentation/technical/partial-clone.txt b/third_party/git/Documentation/technical/partial-clone.txt index 896c7b387886..0780d30caca6 100644 --- a/third_party/git/Documentation/technical/partial-clone.txt +++ b/third_party/git/Documentation/technical/partial-clone.txt @@ -30,12 +30,20 @@ advance* during clone and fetch operations and thereby reduce download times and disk usage. Missing objects can later be "demand fetched" if/when needed. +A remote that can later provide the missing objects is called a +promisor remote, as it promises to send the objects when +requested. Initially Git supported only one promisor remote, the origin +remote from which the user cloned and that was configured in the +"extensions.partialClone" config option. Later support for more than +one promisor remote has been implemented. + Use of partial clone requires that the user be online and the origin -remote be available for on-demand fetching of missing objects. This may -or may not be problematic for the user. For example, if the user can -stay within the pre-selected subset of the source tree, they may not -encounter any missing objects. Alternatively, the user could try to -pre-fetch various objects if they know that they are going offline. +remote or other promisor remotes be available for on-demand fetching +of missing objects. This may or may not be problematic for the user. +For example, if the user can stay within the pre-selected subset of +the source tree, they may not encounter any missing objects. +Alternatively, the user could try to pre-fetch various objects if they +know that they are going offline. Non-Goals @@ -100,18 +108,18 @@ or commits that reference missing trees. Handling Missing Objects ------------------------ -- An object may be missing due to a partial clone or fetch, or missing due - to repository corruption. To differentiate these cases, the local - repository specially indicates such filtered packfiles obtained from the - promisor remote as "promisor packfiles". +- An object may be missing due to a partial clone or fetch, or missing + due to repository corruption. To differentiate these cases, the + local repository specially indicates such filtered packfiles + obtained from promisor remotes as "promisor packfiles". + These promisor packfiles consist of a "<name>.promisor" file with arbitrary contents (like the "<name>.keep" files), in addition to their "<name>.pack" and "<name>.idx" files. - The local repository considers a "promisor object" to be an object that - it knows (to the best of its ability) that the promisor remote has promised - that it has, either because the local repository has that object in one of + it knows (to the best of its ability) that promisor remotes have promised + that they have, either because the local repository has that object in one of its promisor packfiles, or because another promisor object refers to it. + When Git encounters a missing object, Git can see if it is a promisor object @@ -123,12 +131,12 @@ expensive-to-modify list of missing objects.[a] - Since almost all Git code currently expects any referenced object to be present locally and because we do not want to force every command to do a dry-run first, a fallback mechanism is added to allow Git to attempt - to dynamically fetch missing objects from the promisor remote. + to dynamically fetch missing objects from promisor remotes. + When the normal object lookup fails to find an object, Git invokes -fetch-object to try to get the object from the server and then retry -the object lookup. This allows objects to be "faulted in" without -complicated prediction algorithms. +promisor_remote_get_direct() to try to get the object from a promisor +remote and then retry the object lookup. This allows objects to be +"faulted in" without complicated prediction algorithms. + For efficiency reasons, no check as to whether the missing object is actually a promisor object is performed. @@ -157,46 +165,80 @@ and prefetch those objects in bulk. + We are not happy with this global variable and would like to remove it, but that requires significant refactoring of the object code to pass an -additional flag. We hope that concurrent efforts to add an ODB API can -encompass this. +additional flag. Fetching Missing Objects ------------------------ -- Fetching of objects is done using the existing transport mechanism using - transport_fetch_refs(), setting a new transport option - TRANS_OPT_NO_DEPENDENTS to indicate that only the objects themselves are - desired, not any object that they refer to. -+ -Because some transports invoke fetch_pack() in the same process, fetch_pack() -has been updated to not use any object flags when the corresponding argument -(no_dependents) is set. +- Fetching of objects is done by invoking a "git fetch" subprocess. - The local repository sends a request with the hashes of all requested - objects as "want" lines, and does not perform any packfile negotiation. + objects, and does not perform any packfile negotiation. It then receives a packfile. -- Because we are reusing the existing fetch-pack mechanism, fetching +- Because we are reusing the existing fetch mechanism, fetching currently fetches all objects referred to by the requested objects, even though they are not necessary. +Using many promisor remotes +--------------------------- + +Many promisor remotes can be configured and used. + +This allows for example a user to have multiple geographically-close +cache servers for fetching missing blobs while continuing to do +filtered `git-fetch` commands from the central server. + +When fetching objects, promisor remotes are tried one after the other +until all the objects have been fetched. + +Remotes that are considered "promisor" remotes are those specified by +the following configuration variables: + +- `extensions.partialClone = <name>` + +- `remote.<name>.promisor = true` + +- `remote.<name>.partialCloneFilter = ...` + +Only one promisor remote can be configured using the +`extensions.partialClone` config variable. This promisor remote will +be the last one tried when fetching objects. + +We decided to make it the last one we try, because it is likely that +someone using many promisor remotes is doing so because the other +promisor remotes are better for some reason (maybe they are closer or +faster for some kind of objects) than the origin, and the origin is +likely to be the remote specified by extensions.partialClone. + +This justification is not very strong, but one choice had to be made, +and anyway the long term plan should be to make the order somehow +fully configurable. + +For now though the other promisor remotes will be tried in the order +they appear in the config file. + Current Limitations ------------------- -- The remote used for a partial clone (or the first partial fetch - following a regular clone) is marked as the "promisor remote". +- It is not possible to specify the order in which the promisor + remotes are tried in other ways than the order in which they appear + in the config file. + -We are currently limited to a single promisor remote and only that -remote may be used for subsequent partial fetches. +It is also not possible to specify an order to be used when fetching +from one remote and a different order when fetching from another +remote. + +- It is not possible to push only specific objects to a promisor + remote. + -We accept this limitation because we believe initial users of this -feature will be using it on repositories with a strong single central -server. +It is not possible to push at the same time to multiple promisor +remote in a specific order. -- Dynamic object fetching will only ask the promisor remote for missing - objects. We assume that the promisor remote has a complete view of the +- Dynamic object fetching will only ask promisor remotes for missing + objects. We assume that promisor remotes have a complete view of the repository and can satisfy all such requests. - Repack essentially treats promisor and non-promisor packfiles as 2 @@ -218,15 +260,17 @@ server. Future Work ----------- -- Allow more than one promisor remote and define a strategy for fetching - missing objects from specific promisor remotes or of iterating over the - set of promisor remotes until a missing object is found. +- Improve the way to specify the order in which promisor remotes are + tried. + -A user might want to have multiple geographically-close cache servers -for fetching missing blobs while continuing to do filtered `git-fetch` -commands from the central server, for example. +For example this could allow to specify explicitly something like: +"When fetching from this remote, I want to use these promisor remotes +in this order, though, when pushing or fetching to that remote, I want +to use those promisor remotes in that order." + +- Allow pushing to promisor remotes. + -Or the user might want to work in a triangular work flow with multiple +The user might want to work in a triangular work flow with multiple promisor remotes that each have an incomplete view of the repository. - Allow repack to work on promisor packfiles (while keeping them distinct @@ -299,26 +343,26 @@ Related Links [0] https://crbug.com/git/2 Bug#2: Partial Clone -[1] https://public-inbox.org/git/20170113155253.1644-1-benpeart@microsoft.com/ + +[1] https://lore.kernel.org/git/20170113155253.1644-1-benpeart@microsoft.com/ + Subject: [RFC] Add support for downloading blobs on demand + Date: Fri, 13 Jan 2017 10:52:53 -0500 -[2] https://public-inbox.org/git/cover.1506714999.git.jonathantanmy@google.com/ + +[2] https://lore.kernel.org/git/cover.1506714999.git.jonathantanmy@google.com/ + Subject: [PATCH 00/18] Partial clone (from clone to lazy fetch in 18 patches) + Date: Fri, 29 Sep 2017 13:11:36 -0700 -[3] https://public-inbox.org/git/20170426221346.25337-1-jonathantanmy@google.com/ + +[3] https://lore.kernel.org/git/20170426221346.25337-1-jonathantanmy@google.com/ + Subject: Proposal for missing blob support in Git repos + Date: Wed, 26 Apr 2017 15:13:46 -0700 -[4] https://public-inbox.org/git/1488999039-37631-1-git-send-email-git@jeffhostetler.com/ + +[4] https://lore.kernel.org/git/1488999039-37631-1-git-send-email-git@jeffhostetler.com/ + Subject: [PATCH 00/10] RFC Partial Clone and Fetch + Date: Wed, 8 Mar 2017 18:50:29 +0000 -[5] https://public-inbox.org/git/20170505152802.6724-1-benpeart@microsoft.com/ + +[5] https://lore.kernel.org/git/20170505152802.6724-1-benpeart@microsoft.com/ + Subject: [PATCH v7 00/10] refactor the filter process code into a reusable module + Date: Fri, 5 May 2017 11:27:52 -0400 -[6] https://public-inbox.org/git/20170714132651.170708-1-benpeart@microsoft.com/ + +[6] https://lore.kernel.org/git/20170714132651.170708-1-benpeart@microsoft.com/ + Subject: [RFC/PATCH v2 0/1] Add support for downloading blobs on demand + Date: Fri, 14 Jul 2017 09:26:50 -0400 diff --git a/third_party/git/Documentation/technical/protocol-capabilities.txt b/third_party/git/Documentation/technical/protocol-capabilities.txt index 2b267c0da6b2..ba869a7d366a 100644 --- a/third_party/git/Documentation/technical/protocol-capabilities.txt +++ b/third_party/git/Documentation/technical/protocol-capabilities.txt @@ -22,9 +22,9 @@ was sent. Server MUST NOT ignore capabilities that client requested and server advertised. As a consequence of these rules, server MUST NOT advertise capabilities it does not understand. -The 'atomic', 'report-status', 'delete-refs', 'quiet', and 'push-cert' -capabilities are sent and recognized by the receive-pack (push to server) -process. +The 'atomic', 'report-status', 'report-status-v2', 'delete-refs', 'quiet', +and 'push-cert' capabilities are sent and recognized by the receive-pack +(push to server) process. The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized by both upload-pack and receive-pack protocols. The 'agent' capability @@ -176,6 +176,21 @@ agent strings are purely informative for statistics and debugging purposes, and MUST NOT be used to programmatically assume the presence or absence of particular features. +object-format +------------- + +This capability, which takes a hash algorithm as an argument, indicates +that the server supports the given hash algorithms. It may be sent +multiple times; if so, the first one given is the one used in the ref +advertisement. + +When provided by the client, this indicates that it intends to use the +given hash algorithm to communicate. The algorithm provided must be one +that the server supports. + +If this capability is not provided, it is assumed that the only +supported algorithm is SHA-1. + symref ------ @@ -269,6 +284,17 @@ each reference was updated successfully. If any of those were not successful, it will send back an error message. See pack-protocol.txt for example messages. +report-status-v2 +---------------- + +Capability 'report-status-v2' extends capability 'report-status' by +adding new "option" directives in order to support reference rewritten by +the "proc-receive" hook. The "proc-receive" hook may handle a command +for a pseudo-reference which may create or update a reference with +different name, new-oid, and old-oid. While the capability +'report-status' cannot report for such case. See pack-protocol.txt +for details. + delete-refs ----------- @@ -309,15 +335,19 @@ allow-tip-sha1-in-want ---------------------- If the upload-pack server advertises this capability, fetch-pack may -send "want" lines with SHA-1s that exist at the server but are not -advertised by upload-pack. +send "want" lines with object names that exist at the server but are not +advertised by upload-pack. For historical reasons, the name of this +capability contains "sha1". Object names are always given using the +object format negotiated through the 'object-format' capability. allow-reachable-sha1-in-want ---------------------------- If the upload-pack server advertises this capability, fetch-pack may -send "want" lines with SHA-1s that exist at the server but are not -advertised by upload-pack. +send "want" lines with object names that exist at the server but are not +advertised by upload-pack. For historical reasons, the name of this +capability contains "sha1". Object names are always given using the +object format negotiated through the 'object-format' capability. push-cert=<nonce> ----------------- diff --git a/third_party/git/Documentation/technical/protocol-v2.txt b/third_party/git/Documentation/technical/protocol-v2.txt index 40f91f6b1ee1..e597b74da39d 100644 --- a/third_party/git/Documentation/technical/protocol-v2.txt +++ b/third_party/git/Documentation/technical/protocol-v2.txt @@ -33,6 +33,8 @@ In protocol v2 these special packets will have the following semantics: * '0000' Flush Packet (flush-pkt) - indicates the end of a message * '0001' Delimiter Packet (delim-pkt) - separates sections of a message + * '0002' Message Packet (response-end-pkt) - indicates the end of a response + for stateless connections Initial Client Request ---------------------- @@ -252,7 +254,7 @@ A `fetch` request can take the following arguments: ofs-delta Indicate that the client understands PACKv2 with delta referring to its base by position in pack rather than by an oid. That is, - they can read OBJ_OFS_DELTA (ake type 6) in a packfile. + they can read OBJ_OFS_DELTA (aka type 6) in a packfile. If the 'shallow' feature is advertised the following arguments can be included in the clients request as well as the potential addition of the @@ -323,13 +325,26 @@ included in the client's request: indicating its sideband (1, 2, or 3), and the server may send "0005\2" (a PKT-LINE of sideband 2 with no payload) as a keepalive packet. +If the 'packfile-uris' feature is advertised, the following argument +can be included in the client's request as well as the potential +addition of the 'packfile-uris' section in the server's response as +explained below. + + packfile-uris <comma-separated list of protocols> + Indicates to the server that the client is willing to receive + URIs of any of the given protocols in place of objects in the + sent packfile. Before performing the connectivity check, the + client should download from all given URIs. Currently, the + protocols supported are "http" and "https". + The response of `fetch` is broken into a number of sections separated by delimiter packets (0001), with each section beginning with its section -header. +header. Most sections are sent only when the packfile is sent. - output = *section - section = (acknowledgments | shallow-info | wanted-refs | packfile) - (flush-pkt | delim-pkt) + output = acknowledgements flush-pkt | + [acknowledgments delim-pkt] [shallow-info delim-pkt] + [wanted-refs delim-pkt] [packfile-uris delim-pkt] + packfile flush-pkt acknowledgments = PKT-LINE("acknowledgments" LF) (nak | *ack) @@ -347,13 +362,17 @@ header. *PKT-LINE(wanted-ref LF) wanted-ref = obj-id SP refname + packfile-uris = PKT-LINE("packfile-uris" LF) *packfile-uri + packfile-uri = PKT-LINE(40*(HEXDIGIT) SP *%x20-ff LF) + packfile = PKT-LINE("packfile" LF) *PKT-LINE(%x01-03 *%x00-ff) acknowledgments section - * If the client determines that it is finished with negotiations - by sending a "done" line, the acknowledgments sections MUST be - omitted from the server's response. + * If the client determines that it is finished with negotiations by + sending a "done" line (thus requiring the server to send a packfile), + the acknowledgments sections MUST be omitted from the server's + response. * Always begins with the section header "acknowledgments" @@ -404,9 +423,6 @@ header. which the client has not indicated was shallow as a part of its request. - * This section is only included if a packfile section is also - included in the response. - wanted-refs section * This section is only included if the client has requested a ref using a 'want-ref' line and if a packfile section is also @@ -420,6 +436,20 @@ header. * The server MUST NOT send any refs which were not requested using 'want-ref' lines. + packfile-uris section + * This section is only included if the client sent + 'packfile-uris' and the server has at least one such URI to + send. + + * Always begins with the section header "packfile-uris". + + * For each URI the server sends, it sends a hash of the pack's + contents (as output by git index-pack) followed by the URI. + + * The hashes are 40 hex characters long. When Git upgrades to a new + hash algorithm, this might need to be updated. (It should match + whatever index-pack outputs after "pack\t" or "keep\t". + packfile section * This section is only included if the client has sent 'want' lines in its request and either requested that no more @@ -453,3 +483,12 @@ included in a request. This is done by sending each option as a a request. The provided options must not contain a NUL or LF character. + + object-format +~~~~~~~~~~~~~~~ + +The server can advertise the `object-format` capability with a value `X` (in the +form `object-format=X`) to notify the client that the server is able to deal +with objects using hash algorithm X. If not specified, the server is assumed to +only handle SHA-1. If the client would like to use a hash algorithm other than +SHA-1, it should specify its object-format string. diff --git a/third_party/git/Documentation/technical/racy-git.txt b/third_party/git/Documentation/technical/racy-git.txt index 4a8be4d144cf..ceda4bbfda4d 100644 --- a/third_party/git/Documentation/technical/racy-git.txt +++ b/third_party/git/Documentation/technical/racy-git.txt @@ -51,7 +51,7 @@ of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git only fixes the issue for file systems with exactly 1 ns or 1 s resolution. Other file systems are still broken in current Linux kernels (e.g. CEPH, CIFS, NTFS, UDF), see -https://lkml.org/lkml/2015/6/9/714 +https://lore.kernel.org/lkml/5577240D.7020309@gmail.com/ Racy Git -------- diff --git a/third_party/git/Documentation/technical/reftable.txt b/third_party/git/Documentation/technical/reftable.txt new file mode 100644 index 000000000000..2951840e9c9b --- /dev/null +++ b/third_party/git/Documentation/technical/reftable.txt @@ -0,0 +1,1083 @@ +reftable +-------- + +Overview +~~~~~~~~ + +Problem statement +^^^^^^^^^^^^^^^^^ + +Some repositories contain a lot of references (e.g. android at 866k, +rails at 31k). The existing packed-refs format takes up a lot of space +(e.g. 62M), and does not scale with additional references. Lookup of a +single reference requires linearly scanning the file. + +Atomic pushes modifying multiple references require copying the entire +packed-refs file, which can be a considerable amount of data moved +(e.g. 62M in, 62M out) for even small transactions (2 refs modified). + +Repositories with many loose references occupy a large number of disk +blocks from the local file system, as each reference is its own file +storing 41 bytes (and another file for the corresponding reflog). This +negatively affects the number of inodes available when a large number of +repositories are stored on the same filesystem. Readers can be penalized +due to the larger number of syscalls required to traverse and read the +`$GIT_DIR/refs` directory. + + +Objectives +^^^^^^^^^^ + +* Near constant time lookup for any single reference, even when the +repository is cold and not in process or kernel cache. +* Near constant time verification if an object name is referred to by at least +one reference (for allow-tip-sha1-in-want). +* Efficient enumeration of an entire namespace, such as `refs/tags/`. +* Support atomic push with `O(size_of_update)` operations. +* Combine reflog storage with ref storage for small transactions. +* Separate reflog storage for base refs and historical logs. + +Description +^^^^^^^^^^^ + +A reftable file is a portable binary file format customized for +reference storage. References are sorted, enabling linear scans, binary +search lookup, and range scans. + +Storage in the file is organized into variable sized blocks. Prefix +compression is used within a single block to reduce disk space. Block +size and alignment is tunable by the writer. + +Performance +^^^^^^^^^^^ + +Space used, packed-refs vs. reftable: + +[cols=",>,>,>,>,>",options="header",] +|=============================================================== +|repository |packed-refs |reftable |% original |avg ref |avg obj +|android |62.2 M |36.1 M |58.0% |33 bytes |5 bytes +|rails |1.8 M |1.1 M |57.7% |29 bytes |4 bytes +|git |78.7 K |48.1 K |61.0% |50 bytes |4 bytes +|git (heads) |332 b |269 b |81.0% |33 bytes |0 bytes +|=============================================================== + +Scan (read 866k refs), by reference name lookup (single ref from 866k +refs), and by SHA-1 lookup (refs with that SHA-1, from 866k refs): + +[cols=",>,>,>,>",options="header",] +|========================================================= +|format |cache |scan |by name |by SHA-1 +|packed-refs |cold |402 ms |409,660.1 usec |412,535.8 usec +|packed-refs |hot | |6,844.6 usec |20,110.1 usec +|reftable |cold |112 ms |33.9 usec |323.2 usec +|reftable |hot | |20.2 usec |320.8 usec +|========================================================= + +Space used for 149,932 log entries for 43,061 refs, reflog vs. reftable: + +[cols=",>,>",options="header",] +|================================ +|format |size |avg entry +|$GIT_DIR/logs |173 M |1209 bytes +|reftable |5 M |37 bytes +|================================ + +Details +~~~~~~~ + +Peeling +^^^^^^^ + +References stored in a reftable are peeled, a record for an annotated +(or signed) tag records both the tag object, and the object it refers +to. This is analogous to storage in the packed-refs format. + +Reference name encoding +^^^^^^^^^^^^^^^^^^^^^^^ + +Reference names are an uninterpreted sequence of bytes that must pass +linkgit:git-check-ref-format[1] as a valid reference name. + +Key unicity +^^^^^^^^^^^ + +Each entry must have a unique key; repeated keys are disallowed. + +Network byte order +^^^^^^^^^^^^^^^^^^ + +All multi-byte, fixed width fields are in network byte order. + +Varint encoding +^^^^^^^^^^^^^^^ + +Varint encoding is identical to the ofs-delta encoding method used +within pack files. + +Decoder works such as: + +.... +val = buf[ptr] & 0x7f +while (buf[ptr] & 0x80) { + ptr++ + val = ((val + 1) << 7) | (buf[ptr] & 0x7f) +} +.... + +Ordering +^^^^^^^^ + +Blocks are lexicographically ordered by their first reference. + +Directory/file conflicts +^^^^^^^^^^^^^^^^^^^^^^^^ + +The reftable format accepts both `refs/heads/foo` and +`refs/heads/foo/bar` as distinct references. + +This property is useful for retaining log records in reftable, but may +confuse versions of Git using `$GIT_DIR/refs` directory tree to maintain +references. Users of reftable may choose to continue to reject `foo` and +`foo/bar` type conflicts to prevent problems for peers. + +File format +~~~~~~~~~~~ + +Structure +^^^^^^^^^ + +A reftable file has the following high-level structure: + +.... +first_block { + header + first_ref_block +} +ref_block* +ref_index* +obj_block* +obj_index* +log_block* +log_index* +footer +.... + +A log-only file omits the `ref_block`, `ref_index`, `obj_block` and +`obj_index` sections, containing only the file header and log block: + +.... +first_block { + header +} +log_block* +log_index* +footer +.... + +in a log-only file the first log block immediately follows the file +header, without padding to block alignment. + +Block size +^^^^^^^^^^ + +The file's block size is arbitrarily determined by the writer, and does +not have to be a power of 2. The block size must be larger than the +longest reference name or log entry used in the repository, as +references cannot span blocks. + +Powers of two that are friendly to the virtual memory system or +filesystem (such as 4k or 8k) are recommended. Larger sizes (64k) can +yield better compression, with a possible increased cost incurred by +readers during access. + +The largest block size is `16777215` bytes (15.99 MiB). + +Block alignment +^^^^^^^^^^^^^^^ + +Writers may choose to align blocks at multiples of the block size by +including `padding` filled with NUL bytes at the end of a block to round +out to the chosen alignment. When alignment is used, writers must +specify the alignment with the file header's `block_size` field. + +Block alignment is not required by the file format. Unaligned files must +set `block_size = 0` in the file header, and omit `padding`. Unaligned +files with more than one ref block must include the link:#Ref-index[ref +index] to support fast lookup. Readers must be able to read both aligned +and non-aligned files. + +Very small files (e.g. a single ref block) may omit `padding` and the ref +index to reduce total file size. + +Header (version 1) +^^^^^^^^^^^^^^^^^^ + +A 24-byte header appears at the beginning of the file: + +.... +'REFT' +uint8( version_number = 1 ) +uint24( block_size ) +uint64( min_update_index ) +uint64( max_update_index ) +.... + +Aligned files must specify `block_size` to configure readers with the +expected block alignment. Unaligned files must set `block_size = 0`. + +The `min_update_index` and `max_update_index` describe bounds for the +`update_index` field of all log records in this file. When reftables are +used in a stack for link:#Update-transactions[transactions], these +fields can order the files such that the prior file's +`max_update_index + 1` is the next file's `min_update_index`. + +Header (version 2) +^^^^^^^^^^^^^^^^^^ + +A 28-byte header appears at the beginning of the file: + +.... +'REFT' +uint8( version_number = 2 ) +uint24( block_size ) +uint64( min_update_index ) +uint64( max_update_index ) +uint32( hash_id ) +.... + +The header is identical to `version_number=1`, with the 4-byte hash ID +("sha1" for SHA1 and "s256" for SHA-256) append to the header. + +For maximum backward compatibility, it is recommended to use version 1 when +writing SHA1 reftables. + +First ref block +^^^^^^^^^^^^^^^ + +The first ref block shares the same block as the file header, and is 24 +bytes smaller than all other blocks in the file. The first block +immediately begins after the file header, at position 24. + +If the first block is a log block (a log-only file), its block header +begins immediately at position 24. + +Ref block format +^^^^^^^^^^^^^^^^ + +A ref block is written as: + +.... +'r' +uint24( block_len ) +ref_record+ +uint24( restart_offset )+ +uint16( restart_count ) + +padding? +.... + +Blocks begin with `block_type = 'r'` and a 3-byte `block_len` which +encodes the number of bytes in the block up to, but not including the +optional `padding`. This is always less than or equal to the file's +block size. In the first ref block, `block_len` includes 24 bytes for +the file header. + +The 2-byte `restart_count` stores the number of entries in the +`restart_offset` list, which must not be empty. Readers can use +`restart_count` to binary search between restarts before starting a +linear scan. + +Exactly `restart_count` 3-byte `restart_offset` values precedes the +`restart_count`. Offsets are relative to the start of the block and +refer to the first byte of any `ref_record` whose name has not been +prefix compressed. Entries in the `restart_offset` list must be sorted, +ascending. Readers can start linear scans from any of these records. + +A variable number of `ref_record` fill the middle of the block, +describing reference names and values. The format is described below. + +As the first ref block shares the first file block with the file header, +all `restart_offset` in the first block are relative to the start of the +file (position 0), and include the file header. This forces the first +`restart_offset` to be `28`. + +ref record +++++++++++ + +A `ref_record` describes a single reference, storing both the name and +its value(s). Records are formatted as: + +.... +varint( prefix_length ) +varint( (suffix_length << 3) | value_type ) +suffix +varint( update_index_delta ) +value? +.... + +The `prefix_length` field specifies how many leading bytes of the prior +reference record's name should be copied to obtain this reference's +name. This must be 0 for the first reference in any block, and also must +be 0 for any `ref_record` whose offset is listed in the `restart_offset` +table at the end of the block. + +Recovering a reference name from any `ref_record` is a simple concat: + +.... +this_name = prior_name[0..prefix_length] + suffix +.... + +The `suffix_length` value provides the number of bytes available in +`suffix` to copy from `suffix` to complete the reference name. + +The `update_index` that last modified the reference can be obtained by +adding `update_index_delta` to the `min_update_index` from the file +header: `min_update_index + update_index_delta`. + +The `value` follows. Its format is determined by `value_type`, one of +the following: + +* `0x0`: deletion; no value data (see transactions, below) +* `0x1`: one object name; value of the ref +* `0x2`: two object names; value of the ref, peeled target +* `0x3`: symbolic reference: `varint( target_len ) target` + +Symbolic references use `0x3`, followed by the complete name of the +reference target. No compression is applied to the target name. + +Types `0x4..0x7` are reserved for future use. + +Ref index +^^^^^^^^^ + +The ref index stores the name of the last reference from every ref block +in the file, enabling reduced disk seeks for lookups. Any reference can +be found by searching the index, identifying the containing block, and +searching within that block. + +The index may be organized into a multi-level index, where the 1st level +index block points to additional ref index blocks (2nd level), which may +in turn point to either additional index blocks (e.g. 3rd level) or ref +blocks (leaf level). Disk reads required to access a ref go up with +higher index levels. Multi-level indexes may be required to ensure no +single index block exceeds the file format's max block size of +`16777215` bytes (15.99 MiB). To achieve constant O(1) disk seeks for +lookups the index must be a single level, which is permitted to exceed +the file's configured block size, but not the format's max block size of +15.99 MiB. + +If present, the ref index block(s) appears after the last ref block. + +If there are at least 4 ref blocks, a ref index block should be written +to improve lookup times. Cold reads using the index require 2 disk reads +(read index, read block), and binary searching < 4 blocks also requires +<= 2 reads. Omitting the index block from smaller files saves space. + +If the file is unaligned and contains more than one ref block, the ref +index must be written. + +Index block format: + +.... +'i' +uint24( block_len ) +index_record+ +uint24( restart_offset )+ +uint16( restart_count ) + +padding? +.... + +The index blocks begin with `block_type = 'i'` and a 3-byte `block_len` +which encodes the number of bytes in the block, up to but not including +the optional `padding`. + +The `restart_offset` and `restart_count` fields are identical in format, +meaning and usage as in ref blocks. + +To reduce the number of reads required for random access in very large +files the index block may be larger than other blocks. However, readers +must hold the entire index in memory to benefit from this, so it's a +time-space tradeoff in both file size and reader memory. + +Increasing the file's block size decreases the index size. Alternatively +a multi-level index may be used, keeping index blocks within the file's +block size, but increasing the number of blocks that need to be +accessed. + +index record +++++++++++++ + +An index record describes the last entry in another block. Index records +are written as: + +.... +varint( prefix_length ) +varint( (suffix_length << 3) | 0 ) +suffix +varint( block_position ) +.... + +Index records use prefix compression exactly like `ref_record`. + +Index records store `block_position` after the suffix, specifying the +absolute position in bytes (from the start of the file) of the block +that ends with this reference. Readers can seek to `block_position` to +begin reading the block header. + +Readers must examine the block header at `block_position` to determine +if the next block is another level index block, or the leaf-level ref +block. + +Reading the index ++++++++++++++++++ + +Readers loading the ref index must first read the footer (below) to +obtain `ref_index_position`. If not present, the position will be 0. The +`ref_index_position` is for the 1st level root of the ref index. + +Obj block format +^^^^^^^^^^^^^^^^ + +Object blocks are optional. Writers may choose to omit object blocks, +especially if readers will not use the object name to ref mapping. + +Object blocks use unique, abbreviated 2-32 object name keys, mapping to +ref blocks containing references pointing to that object directly, or as +the peeled value of an annotated tag. Like ref blocks, object blocks use +the file's standard block size. The abbrevation length is available in +the footer as `obj_id_len`. + +To save space in small files, object blocks may be omitted if the ref +index is not present, as brute force search will only need to read a few +ref blocks. When missing, readers should brute force a linear search of +all references to lookup by object name. + +An object block is written as: + +.... +'o' +uint24( block_len ) +obj_record+ +uint24( restart_offset )+ +uint16( restart_count ) + +padding? +.... + +Fields are identical to ref block. Binary search using the restart table +works the same as in reference blocks. + +Because object names are abbreviated by writers to the shortest unique +abbreviation within the reftable, obj key lengths have a variable length. Their +length must be at least 2 bytes. Readers must compare only for common prefix +match within an obj block or obj index. + +obj record +++++++++++ + +An `obj_record` describes a single object abbreviation, and the blocks +containing references using that unique abbreviation: + +.... +varint( prefix_length ) +varint( (suffix_length << 3) | cnt_3 ) +suffix +varint( cnt_large )? +varint( position_delta )* +.... + +Like in reference blocks, abbreviations are prefix compressed within an +obj block. On large reftables with many unique objects, higher block +sizes (64k), and higher restart interval (128), a `prefix_length` of 2 +or 3 and `suffix_length` of 3 may be common in obj records (unique +abbreviation of 5-6 raw bytes, 10-12 hex digits). + +Each record contains `position_count` number of positions for matching +ref blocks. For 1-7 positions the count is stored in `cnt_3`. When +`cnt_3 = 0` the actual count follows in a varint, `cnt_large`. + +The use of `cnt_3` bets most objects are pointed to by only a single +reference, some may be pointed to by a couple of references, and very +few (if any) are pointed to by more than 7 references. + +A special case exists when `cnt_3 = 0` and `cnt_large = 0`: there are no +`position_delta`, but at least one reference starts with this +abbreviation. A reader that needs exact reference names must scan all +references to find which specific references have the desired object. +Writers should use this format when the `position_delta` list would have +overflowed the file's block size due to a high number of references +pointing to the same object. + +The first `position_delta` is the position from the start of the file. +Additional `position_delta` entries are sorted ascending and relative to +the prior entry, e.g. a reader would perform: + +.... +pos = position_delta[0] +prior = pos +for (j = 1; j < position_count; j++) { + pos = prior + position_delta[j] + prior = pos +} +.... + +With a position in hand, a reader must linearly scan the ref block, +starting from the first `ref_record`, testing each reference's object names +(for `value_type = 0x1` or `0x2`) for full equality. Faster searching by +object name within a single ref block is not supported by the reftable format. +Smaller block sizes reduce the number of candidates this step must +consider. + +Obj index +^^^^^^^^^ + +The obj index stores the abbreviation from the last entry for every obj +block in the file, enabling reduced disk seeks for all lookups. It is +formatted exactly the same as the ref index, but refers to obj blocks. + +The obj index should be present if obj blocks are present, as obj blocks +should only be written in larger files. + +Readers loading the obj index must first read the footer (below) to +obtain `obj_index_position`. If not present, the position will be 0. + +Log block format +^^^^^^^^^^^^^^^^ + +Unlike ref and obj blocks, log blocks are always unaligned. + +Log blocks are variable in size, and do not match the `block_size` +specified in the file header or footer. Writers should choose an +appropriate buffer size to prepare a log block for deflation, such as +`2 * block_size`. + +A log block is written as: + +.... +'g' +uint24( block_len ) +zlib_deflate { + log_record+ + uint24( restart_offset )+ + uint16( restart_count ) +} +.... + +Log blocks look similar to ref blocks, except `block_type = 'g'`. + +The 4-byte block header is followed by the deflated block contents using +zlib deflate. The `block_len` in the header is the inflated size +(including 4-byte block header), and should be used by readers to +preallocate the inflation output buffer. A log block's `block_len` may +exceed the file's block size. + +Offsets within the log block (e.g. `restart_offset`) still include the +4-byte header. Readers may prefer prefixing the inflation output buffer +with the 4-byte header. + +Within the deflate container, a variable number of `log_record` describe +reference changes. The log record format is described below. See ref +block format (above) for a description of `restart_offset` and +`restart_count`. + +Because log blocks have no alignment or padding between blocks, readers +must keep track of the bytes consumed by the inflater to know where the +next log block begins. + +log record +++++++++++ + +Log record keys are structured as: + +.... +ref_name '\0' reverse_int64( update_index ) +.... + +where `update_index` is the unique transaction identifier. The +`update_index` field must be unique within the scope of a `ref_name`. +See the update transactions section below for further details. + +The `reverse_int64` function inverses the value so lexicographical +ordering the network byte order encoding sorts the more recent records +with higher `update_index` values first: + +.... +reverse_int64(int64 t) { + return 0xffffffffffffffff - t; +} +.... + +Log records have a similar starting structure to ref and index records, +utilizing the same prefix compression scheme applied to the log record +key described above. + +.... + varint( prefix_length ) + varint( (suffix_length << 3) | log_type ) + suffix + log_data { + old_id + new_id + varint( name_length ) name + varint( email_length ) email + varint( time_seconds ) + sint16( tz_offset ) + varint( message_length ) message + }? +.... + +Log record entries use `log_type` to indicate what follows: + +* `0x0`: deletion; no log data. +* `0x1`: standard git reflog data using `log_data` above. + +The `log_type = 0x0` is mostly useful for `git stash drop`, removing an +entry from the reflog of `refs/stash` in a transaction file (below), +without needing to rewrite larger files. Readers reading a stack of +reflogs must treat this as a deletion. + +For `log_type = 0x1`, the `log_data` section follows +linkgit:git-update-ref[1] logging and includes: + +* two object names (old id, new id) +* varint string of committer's name +* varint string of committer's email +* varint time in seconds since epoch (Jan 1, 1970) +* 2-byte timezone offset in minutes (signed) +* varint string of message + +`tz_offset` is the absolute number of minutes from GMT the committer was +at the time of the update. For example `GMT-0800` is encoded in reftable +as `sint16(-480)` and `GMT+0230` is `sint16(150)`. + +The committer email does not contain `<` or `>`, it's the value normally +found between the `<>` in a git commit object header. + +The `message_length` may be 0, in which case there was no message +supplied for the update. + +Contrary to traditional reflog (which is a file), renames are encoded as +a combination of ref deletion and ref creation. A deletion is a log +record with a zero new_id, and a creation is a log record with a zero old_id. + +Reading the log ++++++++++++++++ + +Readers accessing the log must first read the footer (below) to +determine the `log_position`. The first block of the log begins at +`log_position` bytes since the start of the file. The `log_position` is +not block aligned. + +Importing logs +++++++++++++++ + +When importing from `$GIT_DIR/logs` writers should globally order all +log records roughly by timestamp while preserving file order, and assign +unique, increasing `update_index` values for each log line. Newer log +records get higher `update_index` values. + +Although an import may write only a single reftable file, the reftable +file must span many unique `update_index`, as each log line requires its +own `update_index` to preserve semantics. + +Log index +^^^^^^^^^ + +The log index stores the log key +(`refname \0 reverse_int64(update_index)`) for the last log record of +every log block in the file, supporting bounded-time lookup. + +A log index block must be written if 2 or more log blocks are written to +the file. If present, the log index appears after the last log block. +There is no padding used to align the log index to block alignment. + +Log index format is identical to ref index, except the keys are 9 bytes +longer to include `'\0'` and the 8-byte `reverse_int64(update_index)`. +Records use `block_position` to refer to the start of a log block. + +Reading the index ++++++++++++++++++ + +Readers loading the log index must first read the footer (below) to +obtain `log_index_position`. If not present, the position will be 0. + +Footer +^^^^^^ + +After the last block of the file, a file footer is written. It begins +like the file header, but is extended with additional data. + +.... + HEADER + + uint64( ref_index_position ) + uint64( (obj_position << 5) | obj_id_len ) + uint64( obj_index_position ) + + uint64( log_position ) + uint64( log_index_position ) + + uint32( CRC-32 of above ) +.... + +If a section is missing (e.g. ref index) the corresponding position +field (e.g. `ref_index_position`) will be 0. + +* `obj_position`: byte position for the first obj block. +* `obj_id_len`: number of bytes used to abbreviate object names in +obj blocks. +* `log_position`: byte position for the first log block. +* `ref_index_position`: byte position for the start of the ref index. +* `obj_index_position`: byte position for the start of the obj index. +* `log_index_position`: byte position for the start of the log index. + +The size of the footer is 68 bytes for version 1, and 72 bytes for +version 2. + +Reading the footer +++++++++++++++++++ + +Readers must first read the file start to determine the version +number. Then they seek to `file_length - FOOTER_LENGTH` to access the +footer. A trusted external source (such as `stat(2)`) is necessary to +obtain `file_length`. When reading the footer, readers must verify: + +* 4-byte magic is correct +* 1-byte version number is recognized +* 4-byte CRC-32 matches the other 64 bytes (including magic, and +version) + +Once verified, the other fields of the footer can be accessed. + +Empty tables +++++++++++++ + +A reftable may be empty. In this case, the file starts with a header +and is immediately followed by a footer. + +Binary search +^^^^^^^^^^^^^ + +Binary search within a block is supported by the `restart_offset` fields +at the end of the block. Readers can binary search through the restart +table to locate between which two restart points the sought reference or +key should appear. + +Each record identified by a `restart_offset` stores the complete key in +the `suffix` field of the record, making the compare operation during +binary search straightforward. + +Once a restart point lexicographically before the sought reference has +been identified, readers can linearly scan through the following record +entries to locate the sought record, terminating if the current record +sorts after (and therefore the sought key is not present). + +Restart point selection ++++++++++++++++++++++++ + +Writers determine the restart points at file creation. The process is +arbitrary, but every 16 or 64 records is recommended. Every 16 may be +more suitable for smaller block sizes (4k or 8k), every 64 for larger +block sizes (64k). + +More frequent restart points reduces prefix compression and increases +space consumed by the restart table, both of which increase file size. + +Less frequent restart points makes prefix compression more effective, +decreasing overall file size, with increased penalties for readers +walking through more records after the binary search step. + +A maximum of `65535` restart points per block is supported. + +Considerations +~~~~~~~~~~~~~~ + +Lightweight refs dominate +^^^^^^^^^^^^^^^^^^^^^^^^^ + +The reftable format assumes the vast majority of references are single +object names valued with common prefixes, such as Gerrit Code Review's +`refs/changes/` namespace, GitHub's `refs/pulls/` namespace, or many +lightweight tags in the `refs/tags/` namespace. + +Annotated tags storing the peeled object cost an additional object name per +reference. + +Low overhead +^^^^^^^^^^^^ + +A reftable with very few references (e.g. git.git with 5 heads) is 269 +bytes for reftable, vs. 332 bytes for packed-refs. This supports +reftable scaling down for transaction logs (below). + +Block size +^^^^^^^^^^ + +For a Gerrit Code Review type repository with many change refs, larger +block sizes (64 KiB) and less frequent restart points (every 64) yield +better compression due to more references within the block compressing +against the prior reference. + +Larger block sizes reduce the index size, as the reftable will require +fewer blocks to store the same number of references. + +Minimal disk seeks +^^^^^^^^^^^^^^^^^^ + +Assuming the index block has been loaded into memory, binary searching +for any single reference requires exactly 1 disk seek to load the +containing block. + +Scans and lookups dominate +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Scanning all references and lookup by name (or namespace such as +`refs/heads/`) are the most common activities performed on repositories. +Object names are stored directly with references to optimize this use case. + +Logs are infrequently read +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Logs are infrequently accessed, but can be large. Deflating log blocks +saves disk space, with some increased penalty at read time. + +Logs are stored in an isolated section from refs, reducing the burden on +reference readers that want to ignore logs. Further, historical logs can +be isolated into log-only files. + +Logs are read backwards +^^^^^^^^^^^^^^^^^^^^^^^ + +Logs are frequently accessed backwards (most recent N records for master +to answer `master@{4}`), so log records are grouped by reference, and +sorted descending by update index. + +Repository format +~~~~~~~~~~~~~~~~~ + +Version 1 +^^^^^^^^^ + +A repository must set its `$GIT_DIR/config` to configure reftable: + +.... +[core] + repositoryformatversion = 1 +[extensions] + refStorage = reftable +.... + +Layout +^^^^^^ + +A collection of reftable files are stored in the `$GIT_DIR/reftable/` +directory: + +.... +00000001-00000001.log +00000002-00000002.ref +00000003-00000003.ref +.... + +where reftable files are named by a unique name such as produced by the +function `${min_update_index}-${max_update_index}.ref`. + +Log-only files use the `.log` extension, while ref-only and mixed ref +and log files use `.ref`. extension. + +The stack ordering file is `$GIT_DIR/reftable/tables.list` and lists the +current files, one per line, in order, from oldest (base) to newest +(most recent): + +.... +$ cat .git/reftable/tables.list +00000001-00000001.log +00000002-00000002.ref +00000003-00000003.ref +.... + +Readers must read `$GIT_DIR/reftable/tables.list` to determine which +files are relevant right now, and search through the stack in reverse +order (last reftable is examined first). + +Reftable files not listed in `tables.list` may be new (and about to be +added to the stack by the active writer), or ancient and ready to be +pruned. + +Backward compatibility +^^^^^^^^^^^^^^^^^^^^^^ + +Older clients should continue to recognize the directory as a git +repository so they don't look for an enclosing repository in parent +directories. To this end, a reftable-enabled repository must contain the +following dummy files + +* `.git/HEAD`, a regular file containing `ref: refs/heads/.invalid`. +* `.git/refs/`, a directory +* `.git/refs/heads`, a regular file + +Readers +^^^^^^^ + +Readers can obtain a consistent snapshot of the reference space by +following: + +1. Open and read the `tables.list` file. +2. Open each of the reftable files that it mentions. +3. If any of the files is missing, goto 1. +4. Read from the now-open files as long as necessary. + +Update transactions +^^^^^^^^^^^^^^^^^^^ + +Although reftables are immutable, mutations are supported by writing a +new reftable and atomically appending it to the stack: + +1. Acquire `tables.list.lock`. +2. Read `tables.list` to determine current reftables. +3. Select `update_index` to be most recent file's +`max_update_index + 1`. +4. Prepare temp reftable `tmp_XXXXXX`, including log entries. +5. Rename `tmp_XXXXXX` to `${update_index}-${update_index}.ref`. +6. Copy `tables.list` to `tables.list.lock`, appending file from (5). +7. Rename `tables.list.lock` to `tables.list`. + +During step 4 the new file's `min_update_index` and `max_update_index` +are both set to the `update_index` selected by step 3. All log records +for the transaction use the same `update_index` in their keys. This +enables later correlation of which references were updated by the same +transaction. + +Because a single `tables.list.lock` file is used to manage locking, the +repository is single-threaded for writers. Writers may have to busy-spin +(with backoff) around creating `tables.list.lock`, for up to an +acceptable wait period, aborting if the repository is too busy to +mutate. Application servers wrapped around repositories (e.g. Gerrit +Code Review) can layer their own lock/wait queue to improve fairness to +writers. + +Reference deletions +^^^^^^^^^^^^^^^^^^^ + +Deletion of any reference can be explicitly stored by setting the `type` +to `0x0` and omitting the `value` field of the `ref_record`. This serves +as a tombstone, overriding any assertions about the existence of the +reference from earlier files in the stack. + +Compaction +^^^^^^^^^^ + +A partial stack of reftables can be compacted by merging references +using a straightforward merge join across reftables, selecting the most +recent value for output, and omitting deleted references that do not +appear in remaining, lower reftables. + +A compacted reftable should set its `min_update_index` to the smallest +of the input files' `min_update_index`, and its `max_update_index` +likewise to the largest input `max_update_index`. + +For sake of illustration, assume the stack currently consists of +reftable files (from oldest to newest): A, B, C, and D. The compactor is +going to compact B and C, leaving A and D alone. + +1. Obtain lock `tables.list.lock` and read the `tables.list` file. +2. Obtain locks `B.lock` and `C.lock`. Ownership of these locks +prevents other processes from trying to compact these files. +3. Release `tables.list.lock`. +4. Compact `B` and `C` into a temp file +`${min_update_index}-${max_update_index}_XXXXXX`. +5. Reacquire lock `tables.list.lock`. +6. Verify that `B` and `C` are still in the stack, in that order. This +should always be the case, assuming that other processes are adhering to +the locking protocol. +7. Rename `${min_update_index}-${max_update_index}_XXXXXX` to +`${min_update_index}-${max_update_index}.ref`. +8. Write the new stack to `tables.list.lock`, replacing `B` and `C` +with the file from (4). +9. Rename `tables.list.lock` to `tables.list`. +10. Delete `B` and `C`, perhaps after a short sleep to avoid forcing +readers to backtrack. + +This strategy permits compactions to proceed independently of updates. + +Each reftable (compacted or not) is uniquely identified by its name, so +open reftables can be cached by their name. + +Alternatives considered +~~~~~~~~~~~~~~~~~~~~~~~ + +bzip packed-refs +^^^^^^^^^^^^^^^^ + +`bzip2` can significantly shrink a large packed-refs file (e.g. 62 MiB +compresses to 23 MiB, 37%). However the bzip format does not support +random access to a single reference. Readers must inflate and discard +while performing a linear scan. + +Breaking packed-refs into chunks (individually compressing each chunk) +would reduce the amount of data a reader must inflate, but still leaves +the problem of indexing chunks to support readers efficiently locating +the correct chunk. + +Given the compression achieved by reftable's encoding, it does not seem +necessary to add the complexity of bzip/gzip/zlib. + +Michael Haggerty's alternate format +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Michael Haggerty proposed +link:https://lore.kernel.org/git/CAMy9T_HCnyc1g8XWOOWhe7nN0aEFyyBskV2aOMb_fe%2BwGvEJ7A%40mail.gmail.com/[an +alternate] format to reftable on the Git mailing list. This format uses +smaller chunks, without the restart table, and avoids block alignment +with padding. Reflog entries immediately follow each ref, and are thus +interleaved between refs. + +Performance testing indicates reftable is faster for lookups (51% +faster, 11.2 usec vs. 5.4 usec), although reftable produces a slightly +larger file (+ ~3.2%, 28.3M vs 29.2M): + +[cols=">,>,>,>",options="header",] +|===================================== +|format |size |seek cold |seek hot +|mh-alt |28.3 M |23.4 usec |11.2 usec +|reftable |29.2 M |19.9 usec |5.4 usec +|===================================== + +JGit Ketch RefTree +^^^^^^^^^^^^^^^^^^ + +https://dev.eclipse.org/mhonarc/lists/jgit-dev/msg03073.html[JGit Ketch] +proposed +link:https://lore.kernel.org/git/CAJo%3DhJvnAPNAdDcAAwAvU9C4RVeQdoS3Ev9WTguHx4fD0V_nOg%40mail.gmail.com/[RefTree], +an encoding of references inside Git tree objects stored as part of the +repository's object database. + +The RefTree format adds additional load on the object database storage +layer (more loose objects, more objects in packs), and relies heavily on +the packer's delta compression to save space. Namespaces which are flat +(e.g. thousands of tags in refs/tags) initially create very large loose +objects, and so RefTree does not address the problem of copying many +references to modify a handful. + +Flat namespaces are not efficiently searchable in RefTree, as tree +objects in canonical formatting cannot be binary searched. This fails +the need to handle a large number of references in a single namespace, +such as GitHub's `refs/pulls`, or a project with many tags. + +LMDB +^^^^ + +David Turner proposed +https://lore.kernel.org/git/1455772670-21142-26-git-send-email-dturner@twopensource.com/[using +LMDB], as LMDB is lightweight (64k of runtime code) and GPL-compatible +license. + +A downside of LMDB is its reliance on a single C implementation. This +makes embedding inside JGit (a popular reimplementation of Git) +difficult, and hoisting onto virtual storage (for JGit DFS) virtually +impossible. + +A common format that can be supported by all major Git implementations +(git-core, JGit, libgit2) is strongly preferred. diff --git a/third_party/git/Documentation/technical/rerere.txt b/third_party/git/Documentation/technical/rerere.txt index aa22d7ace893..af5f9fc24f93 100644 --- a/third_party/git/Documentation/technical/rerere.txt +++ b/third_party/git/Documentation/technical/rerere.txt @@ -117,7 +117,7 @@ early A became C or B, a late X became Y or Z". We can see there are 4 combinations of ("B or C", "C or B") x ("X or Y", "Y or X"). By sorting, the conflict is given its canonical name, namely, "an -early part became B or C, a late part becames X or Y", and whenever +early part became B or C, a late part became X or Y", and whenever any of these four patterns appear, and we can get to the same conflict and resolution that we saw earlier. diff --git a/third_party/git/Documentation/technical/shallow.txt b/third_party/git/Documentation/technical/shallow.txt index 01dedfe9ffed..f3738baa0f05 100644 --- a/third_party/git/Documentation/technical/shallow.txt +++ b/third_party/git/Documentation/technical/shallow.txt @@ -13,7 +13,7 @@ pretend as if they are root commits (e.g. "git log" traversal stops after showing them; "git fsck" does not complain saying the commits listed on their "parent" lines do not exist). -Each line contains exactly one SHA-1. When read, a commit_graft +Each line contains exactly one object name. When read, a commit_graft will be constructed, which has nr_parent < 0 to make it easier to discern from user provided grafts. |