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diff --git a/Documentation/howto/keep-canonical-history-correct.txt b/Documentation/howto/keep-canonical-history-correct.txt
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+From: Junio C Hamano <gitster@pobox.com>
+Date: Wed, 07 May 2014 13:15:39 -0700
+Subject: Beginner question on "Pull is mostly evil"
+Abstract: This how-to explains a method for keeping a
+ project's history correct when using git pull.
+Content-type: text/asciidoc
+
+Keep authoritative canonical history correct with git pull
+==========================================================
+
+Sometimes a new project integrator will end up with project history
+that appears to be "backwards" from what other project developers
+expect. This howto presents a suggested integration workflow for
+maintaining a central repository.
+
+Suppose that that central repository has this history:
+
+------------
+    ---o---o---A
+------------
+
+which ends at commit `A` (time flows from left to right and each node
+in the graph is a commit, lines between them indicating parent-child
+relationship).
+
+Then you clone it and work on your own commits, which leads you to
+have this history in *your* repository:
+
+------------
+    ---o---o---A---B---C
+------------
+
+Imagine your coworker did the same and built on top of `A` in *his*
+repository in the meantime, and then pushed it to the
+central repository:
+
+------------
+    ---o---o---A---X---Y---Z
+------------
+
+Now, if you `git push` at this point, because your history that leads
+to `C` lacks `X`, `Y` and `Z`, it will fail.  You need to somehow make
+the tip of your history a descendant of `Z`.
+
+One suggested way to solve the problem is "fetch and then merge", aka
+`git pull`. When you fetch, your repository will have a history like
+this:
+
+------------
+    ---o---o---A---B---C
+		\
+		 X---Y---Z
+------------
+
+Once you run merge after that, while still on *your* branch, i.e. `C`,
+you will create a merge `M` and make the history look like this:
+
+------------
+    ---o---o---A---B---C---M
+		\         /
+		 X---Y---Z
+------------
+
+`M` is a descendant of `Z`, so you can push to update the central
+repository.  Such a merge `M` does not lose any commit in both
+histories, so in that sense it may not be wrong, but when people want
+to talk about "the authoritative canonical history that is shared
+among the project participants", i.e. "the trunk", they often view
+it as "commits you see by following the first-parent chain", and use
+this command to view it:
+
+------------
+    $ git log --first-parent
+------------
+
+For all other people who observed the central repository after your
+coworker pushed `Z` but before you pushed `M`, the commit on the trunk
+used to be `o-o-A-X-Y-Z`.  But because you made `M` while you were on
+`C`, `M`'s first parent is `C`, so by pushing `M` to advance the
+central repository, you made `X-Y-Z` a side branch, not on the trunk.
+
+You would rather want to have a history of this shape:
+
+------------
+    ---o---o---A---X---Y---Z---M'
+		\             /
+		 B-----------C
+------------
+
+so that in the first-parent chain, it is clear that the project first
+did `X` and then `Y` and then `Z` and merged a change that consists of
+two commits `B` and `C` that achieves a single goal.  You may have
+worked on fixing the bug #12345 with these two patches, and the merge
+`M'` with swapped parents can say in its log message "Merge
+fix-bug-12345". Having a way to tell `git pull` to create a merge
+but record the parents in reverse order may be a way to do so.
+
+Note that I said "achieves a single goal" above, because this is
+important.  "Swapping the merge order" only covers a special case
+where the project does not care too much about having unrelated
+things done on a single merge but cares a lot about first-parent
+chain.
+
+There are multiple schools of thought about the "trunk" management.
+
+ 1. Some projects want to keep a completely linear history without any
+    merges.  Obviously, swapping the merge order would not match their
+    taste.  You would need to flatten your history on top of the
+    updated upstream to result in a history of this shape instead:
++
+------------
+    ---o---o---A---X---Y---Z---B---C
+------------
++
+with `git pull --rebase` or something.
+
+ 2. Some projects tolerate merges in their history, but do not worry
+    too much about the first-parent order, and allow fast-forward
+    merges.  To them, swapping the merge order does not hurt, but
+    it is unnecessary.
+
+ 3. Some projects want each commit on the "trunk" to do one single
+    thing.  The output of `git log --first-parent` in such a project
+    would show either a merge of a side branch that completes a single
+    theme, or a single commit that completes a single theme by itself.
+    If your two commits `B` and `C` (or they may even be two groups of
+    commits) were solving two independent issues, then the merge `M'`
+    we made in the earlier example by swapping the merge order is
+    still not up to the project standard.  It merges two unrelated
+    efforts `B` and `C` at the same time.
+
+For projects in the last category (Git itself is one of them),
+individual developers would want to prepare a history more like
+this:
+
+------------
+		 C0--C1--C2     topic-c
+		/
+    ---o---o---A                master
+		\
+		 B0--B1--B2     topic-b
+------------
+
+That is, keeping separate topics on separate branches, perhaps like
+so:
+
+------------
+    $ git clone $URL work && cd work
+    $ git checkout -b topic-b master
+    $ ... work to create B0, B1 and B2 to complete one theme
+    $ git checkout -b topic-c master
+    $ ... same for the theme of topic-c
+------------
+
+And then
+
+------------
+    $ git checkout master
+    $ git pull --ff-only
+------------
+
+would grab `X`, `Y` and `Z` from the upstream and advance your master
+branch:
+
+------------
+		 C0--C1--C2     topic-c
+		/
+    ---o---o---A---X---Y---Z    master
+		\
+		 B0--B1--B2     topic-b
+------------
+
+And then you would merge these two branches separately:
+
+------------
+    $ git merge topic-b
+    $ git merge topic-c
+------------
+
+to result in
+
+------------
+		 C0--C1---------C2
+		/                 \
+    ---o---o---A---X---Y---Z---M---N
+		\             /
+		 B0--B1-----B2
+------------
+
+and push it back to the central repository.
+
+It is very much possible that while you are merging topic-b and
+topic-c, somebody again advanced the history in the central repository
+to put `W` on top of `Z`, and make your `git push` fail.
+
+In such a case, you would rewind to discard `M` and `N`, update the
+tip of your 'master' again and redo the two merges:
+
+------------
+    $ git reset --hard origin/master
+    $ git pull --ff-only
+    $ git merge topic-b
+    $ git merge topic-c
+------------
+
+The procedure will result in a history that looks like this:
+
+------------
+		 C0--C1--------------C2
+		/                     \
+    ---o---o---A---X---Y---Z---W---M'--N'
+		\                 /
+		 B0--B1---------B2
+------------
+
+See also http://git-blame.blogspot.com/2013/09/fun-with-first-parent-history.html
diff --git a/Documentation/howto/maintain-git.txt b/Documentation/howto/maintain-git.txt
new file mode 100644
index 000000000000..ca4378740c6a
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+++ b/Documentation/howto/maintain-git.txt
@@ -0,0 +1,449 @@
+From: Junio C Hamano <gitster@pobox.com>
+Date: Wed, 21 Nov 2007 16:32:55 -0800
+Subject: Addendum to "MaintNotes"
+Abstract: Imagine that Git development is racing along as usual, when our friendly
+ neighborhood maintainer is struck down by a wayward bus. Out of the
+ hordes of suckers (loyal developers), you have been tricked (chosen) to
+ step up as the new maintainer. This howto will show you "how to" do it.
+Content-type: text/asciidoc
+
+How to maintain Git
+===================
+
+Activities
+----------
+
+The maintainer's Git time is spent on three activities.
+
+ - Communication (45%)
+
+   Mailing list discussions on general design, fielding user
+   questions, diagnosing bug reports; reviewing, commenting on,
+   suggesting alternatives to, and rejecting patches.
+
+ - Integration (50%)
+
+   Applying new patches from the contributors while spotting and
+   correcting minor mistakes, shuffling the integration and
+   testing branches, pushing the results out, cutting the
+   releases, and making announcements.
+
+ - Own development (5%)
+
+   Scratching my own itch and sending proposed patch series out.
+
+The Policy
+----------
+
+The policy on Integration is informally mentioned in "A Note
+from the maintainer" message, which is periodically posted to
+this mailing list after each feature release is made.
+
+ - Feature releases are numbered as vX.Y.0 and are meant to
+   contain bugfixes and enhancements in any area, including
+   functionality, performance and usability, without regression.
+
+ - One release cycle for a feature release is expected to last for
+   eight to ten weeks.
+
+ - Maintenance releases are numbered as vX.Y.Z and are meant
+   to contain only bugfixes for the corresponding vX.Y.0 feature
+   release and earlier maintenance releases vX.Y.W (W < Z).
+
+ - 'master' branch is used to prepare for the next feature
+   release. In other words, at some point, the tip of 'master'
+   branch is tagged with vX.Y.0.
+
+ - 'maint' branch is used to prepare for the next maintenance
+   release.  After the feature release vX.Y.0 is made, the tip
+   of 'maint' branch is set to that release, and bugfixes will
+   accumulate on the branch, and at some point, the tip of the
+   branch is tagged with vX.Y.1, vX.Y.2, and so on.
+
+ - 'next' branch is used to publish changes (both enhancements
+   and fixes) that (1) have worthwhile goal, (2) are in a fairly
+   good shape suitable for everyday use, (3) but have not yet
+   demonstrated to be regression free.  New changes are tested
+   in 'next' before merged to 'master'.
+
+ - 'pu' branch is used to publish other proposed changes that do
+   not yet pass the criteria set for 'next'.
+
+ - The tips of 'master' and 'maint' branches will not be rewound to
+   allow people to build their own customization on top of them.
+   Early in a new development cycle, 'next' is rewound to the tip of
+   'master' once, but otherwise it will not be rewound until the end
+   of the cycle.
+
+ - Usually 'master' contains all of 'maint' and 'next' contains all
+   of 'master'.  'pu' contains all the topics merged to 'next', but
+   is rebuilt directly on 'master'.
+
+ - The tip of 'master' is meant to be more stable than any
+   tagged releases, and the users are encouraged to follow it.
+
+ - The 'next' branch is where new action takes place, and the
+   users are encouraged to test it so that regressions and bugs
+   are found before new topics are merged to 'master'.
+
+Note that before v1.9.0 release, the version numbers used to be
+structured slightly differently.  vX.Y.Z were feature releases while
+vX.Y.Z.W were maintenance releases for vX.Y.Z.
+
+
+A Typical Git Day
+-----------------
+
+A typical Git day for the maintainer implements the above policy
+by doing the following:
+
+ - Scan mailing list.  Respond with review comments, suggestions
+   etc.  Kibitz.  Collect potentially usable patches from the
+   mailing list.  Patches about a single topic go to one mailbox (I
+   read my mail in Gnus, and type \C-o to save/append messages in
+   files in mbox format).
+
+ - Write his own patches to address issues raised on the list but
+   nobody has stepped up solving.  Send it out just like other
+   contributors do, and pick them up just like patches from other
+   contributors (see above).
+
+ - Review the patches in the saved mailboxes.  Edit proposed log
+   message for typofixes and clarifications, and add Acks
+   collected from the list.  Edit patch to incorporate "Oops,
+   that should have been like this" fixes from the discussion.
+
+ - Classify the collected patches and handle 'master' and
+   'maint' updates:
+
+   - Obviously correct fixes that pertain to the tip of 'maint'
+     are directly applied to 'maint'.
+
+   - Obviously correct fixes that pertain to the tip of 'master'
+     are directly applied to 'master'.
+
+   - Other topics are not handled in this step.
+
+   This step is done with "git am".
+
+     $ git checkout master    ;# or "git checkout maint"
+     $ git am -sc3 mailbox
+     $ make test
+
+   In practice, almost no patch directly goes to 'master' or
+   'maint'.
+
+ - Review the last issue of "What's cooking" message, review the
+   topics ready for merging (topic->master and topic->maint).  Use
+   "Meta/cook -w" script (where Meta/ contains a checkout of the
+   'todo' branch) to aid this step.
+
+   And perform the merge.  Use "Meta/Reintegrate -e" script (see
+   later) to aid this step.
+
+     $ Meta/cook -w last-issue-of-whats-cooking.mbox
+
+     $ git checkout master    ;# or "git checkout maint"
+     $ echo ai/topic | Meta/Reintegrate -e ;# "git merge ai/topic"
+     $ git log -p ORIG_HEAD.. ;# final review
+     $ git diff ORIG_HEAD..   ;# final review
+     $ make test              ;# final review
+
+ - Handle the remaining patches:
+
+   - Anything unobvious that is applicable to 'master' (in other
+     words, does not depend on anything that is still in 'next'
+     and not in 'master') is applied to a new topic branch that
+     is forked from the tip of 'master'.  This includes both
+     enhancements and unobvious fixes to 'master'.  A topic
+     branch is named as ai/topic where "ai" is two-letter string
+     named after author's initial and "topic" is a descriptive name
+     of the topic (in other words, "what's the series is about").
+
+   - An unobvious fix meant for 'maint' is applied to a new
+     topic branch that is forked from the tip of 'maint'.  The
+     topic is named as ai/maint-topic.
+
+   - Changes that pertain to an existing topic are applied to
+     the branch, but:
+
+     - obviously correct ones are applied first;
+
+     - questionable ones are discarded or applied to near the tip;
+
+   - Replacement patches to an existing topic are accepted only
+     for commits not in 'next'.
+
+   The above except the "replacement" are all done with:
+
+     $ git checkout ai/topic ;# or "git checkout -b ai/topic master"
+     $ git am -sc3 mailbox
+
+   while patch replacement is often done by:
+
+     $ git format-patch ai/topic~$n..ai/topic ;# export existing
+
+   then replace some parts with the new patch, and reapplying:
+
+     $ git checkout ai/topic
+     $ git reset --hard ai/topic~$n
+     $ git am -sc3 -s 000*.txt
+
+   The full test suite is always run for 'maint' and 'master'
+   after patch application; for topic branches the tests are run
+   as time permits.
+
+ - Merge maint to master as needed:
+
+     $ git checkout master
+     $ git merge maint
+     $ make test
+
+ - Merge master to next as needed:
+
+     $ git checkout next
+     $ git merge master
+     $ make test
+
+ - Review the last issue of "What's cooking" again and see if topics
+   that are ready to be merged to 'next' are still in good shape
+   (e.g. has there any new issue identified on the list with the
+   series?)
+
+ - Prepare 'jch' branch, which is used to represent somewhere
+   between 'master' and 'pu' and often is slightly ahead of 'next'.
+
+     $ Meta/Reintegrate master..pu >Meta/redo-jch.sh
+
+   The result is a script that lists topics to be merged in order to
+   rebuild 'pu' as the input to Meta/Reintegrate script.  Remove
+   later topics that should not be in 'jch' yet.  Add a line that
+   consists of '### match next' before the name of the first topic
+   in the output that should be in 'jch' but not in 'next' yet.
+
+ - Now we are ready to start merging topics to 'next'.  For each
+   branch whose tip is not merged to 'next', one of three things can
+   happen:
+
+   - The commits are all next-worthy; merge the topic to next;
+   - The new parts are of mixed quality, but earlier ones are
+     next-worthy; merge the early parts to next;
+   - Nothing is next-worthy; do not do anything.
+
+   This step is aided with Meta/redo-jch.sh script created earlier.
+   If a topic that was already in 'next' gained a patch, the script
+   would list it as "ai/topic~1".  To include the new patch to the
+   updated 'next', drop the "~1" part; to keep it excluded, do not
+   touch the line.  If a topic that was not in 'next' should be
+   merged to 'next', add it at the end of the list.  Then:
+
+     $ git checkout -B jch master
+     $ Meta/redo-jch.sh -c1
+
+   to rebuild the 'jch' branch from scratch.  "-c1" tells the script
+   to stop merging at the first line that begins with '###'
+   (i.e. the "### match next" line you added earlier).
+
+   At this point, build-test the result.  It may reveal semantic
+   conflicts (e.g. a topic renamed a variable, another added a new
+   reference to the variable under its old name), in which case
+   prepare an appropriate merge-fix first (see appendix), and
+   rebuild the 'jch' branch from scratch, starting at the tip of
+   'master'.
+
+   Then do the same to 'next'
+
+     $ git checkout next
+     $ sh Meta/redo-jch.sh -c1 -e
+
+   The "-e" option allows the merge message that comes from the
+   history of the topic and the comments in the "What's cooking" to
+   be edited.  The resulting tree should match 'jch' as the same set
+   of topics are merged on 'master'; otherwise there is a mismerge.
+   Investigate why and do not proceed until the mismerge is found
+   and rectified.
+
+     $ git diff jch next
+
+   When all is well, clean up the redo-jch.sh script with
+
+     $ sh Meta/redo-jch.sh -u
+
+   This removes topics listed in the script that have already been
+   merged to 'master'.  This may lose '### match next' marker;
+   add it again to the appropriate place when it happens.
+
+ - Rebuild 'pu'.
+
+     $ Meta/Reintegrate master..pu >Meta/redo-pu.sh
+
+   Edit the result by adding new topics that are not still in 'pu'
+   in the script.  Then
+
+     $ git checkout -B pu jch
+     $ sh Meta/redo-pu.sh
+
+   When all is well, clean up the redo-pu.sh script with
+
+     $ sh Meta/redo-pu.sh -u
+
+   Double check by running
+
+     $ git branch --no-merged pu
+
+   to see there is no unexpected leftover topics.
+
+   At this point, build-test the result for semantic conflicts, and
+   if there are, prepare an appropriate merge-fix first (see
+   appendix), and rebuild the 'pu' branch from scratch, starting at
+   the tip of 'jch'.
+
+ - Update "What's cooking" message to review the updates to
+   existing topics, newly added topics and graduated topics.
+
+   This step is helped with Meta/cook script.
+
+     $ Meta/cook
+
+   This script inspects the history between master..pu, finds tips
+   of topic branches, compares what it found with the current
+   contents in Meta/whats-cooking.txt, and updates that file.
+   Topics not listed in the file but are found in master..pu are
+   added to the "New topics" section, topics listed in the file that
+   are no longer found in master..pu are moved to the "Graduated to
+   master" section, and topics whose commits changed their states
+   (e.g. used to be only in 'pu', now merged to 'next') are updated
+   with change markers "<<" and ">>".
+
+   Look for lines enclosed in "<<" and ">>"; they hold contents from
+   old file that are replaced by this integration round.  After
+   verifying them, remove the old part.  Review the description for
+   each topic and update its doneness and plan as needed.  To review
+   the updated plan, run
+
+     $ Meta/cook -w
+
+   which will pick up comments given to the topics, such as "Will
+   merge to 'next'", etc. (see Meta/cook script to learn what kind
+   of phrases are supported).
+
+ - Compile, test and install all four (five) integration branches;
+   Meta/Dothem script may aid this step.
+
+ - Format documentation if the 'master' branch was updated;
+   Meta/dodoc.sh script may aid this step.
+
+ - Push the integration branches out to public places; Meta/pushall
+   script may aid this step.
+
+Observations
+------------
+
+Some observations to be made.
+
+ * Each topic is tested individually, and also together with other
+   topics cooking first in 'pu', then in 'jch' and then in 'next'.
+   Until it matures, no part of it is merged to 'master'.
+
+ * A topic already in 'next' can get fixes while still in
+   'next'.  Such a topic will have many merges to 'next' (in
+   other words, "git log --first-parent next" will show many
+   "Merge branch 'ai/topic' to next" for the same topic.
+
+ * An unobvious fix for 'maint' is cooked in 'next' and then
+   merged to 'master' to make extra sure it is Ok and then
+   merged to 'maint'.
+
+ * Even when 'next' becomes empty (in other words, all topics
+   prove stable and are merged to 'master' and "git diff master
+   next" shows empty), it has tons of merge commits that will
+   never be in 'master'.
+
+ * In principle, "git log --first-parent master..next" should
+   show nothing but merges (in practice, there are fixup commits
+   and reverts that are not merges).
+
+ * Commits near the tip of a topic branch that are not in 'next'
+   are fair game to be discarded, replaced or rewritten.
+   Commits already merged to 'next' will not be.
+
+ * Being in the 'next' branch is not a guarantee for a topic to
+   be included in the next feature release.  Being in the
+   'master' branch typically is.
+
+
+Appendix
+--------
+
+Preparing a "merge-fix"
+~~~~~~~~~~~~~~~~~~~~~~~
+
+A merge of two topics may not textually conflict but still have
+conflict at the semantic level. A classic example is for one topic
+to rename an variable and all its uses, while another topic adds a
+new use of the variable under its old name. When these two topics
+are merged together, the reference to the variable newly added by
+the latter topic will still use the old name in the result.
+
+The Meta/Reintegrate script that is used by redo-jch and redo-pu
+scripts implements a crude but usable way to work this issue around.
+When the script merges branch $X, it checks if "refs/merge-fix/$X"
+exists, and if so, the effect of it is squashed into the result of
+the mechanical merge.  In other words,
+
+     $ echo $X | Meta/Reintegrate
+
+is roughly equivalent to this sequence:
+
+     $ git merge --rerere-autoupdate $X
+     $ git commit
+     $ git cherry-pick -n refs/merge-fix/$X
+     $ git commit --amend
+
+The goal of this "prepare a merge-fix" step is to come up with a
+commit that can be squashed into a result of mechanical merge to
+correct semantic conflicts.
+
+After finding that the result of merging branch "ai/topic" to an
+integration branch had such a semantic conflict, say pu~4, check the
+problematic merge out on a detached HEAD, edit the working tree to
+fix the semantic conflict, and make a separate commit to record the
+fix-up:
+
+     $ git checkout pu~4
+     $ git show -s --pretty=%s ;# double check
+     Merge branch 'ai/topic' to pu
+     $ edit
+     $ git commit -m 'merge-fix/ai/topic' -a
+
+Then make a reference "refs/merge-fix/ai/topic" to point at this
+result:
+
+     $ git update-ref refs/merge-fix/ai/topic HEAD
+
+Then double check the result by asking Meta/Reintegrate to redo the
+merge:
+
+     $ git checkout pu~5 ;# the parent of the problem merge
+     $ echo ai/topic | Meta/Reintegrate
+     $ git diff pu~4
+
+This time, because you prepared refs/merge-fix/ai/topic, the
+resulting merge should have been tweaked to include the fix for the
+semantic conflict.
+
+Note that this assumes that the order in which conflicting branches
+are merged does not change.  If the reason why merging ai/topic
+branch needs this merge-fix is because another branch merged earlier
+to the integration branch changed the underlying assumption ai/topic
+branch made (e.g. ai/topic branch added a site to refer to a
+variable, while the other branch renamed that variable and adjusted
+existing use sites), and if you changed redo-jch (or redo-pu) script
+to merge ai/topic branch before the other branch, then the above
+merge-fix should not be applied while merging ai/topic, but should
+instead be applied while merging the other branch.  You would need
+to move the fix to apply to the other branch, perhaps like this:
+
+      $ mf=refs/merge-fix
+      $ git update-ref $mf/$the_other_branch $mf/ai/topic
+      $ git update-ref -d $mf/ai/topic
diff --git a/Documentation/howto/new-command.txt b/Documentation/howto/new-command.txt
new file mode 100644
index 000000000000..15a4c8031f1f
--- /dev/null
+++ b/Documentation/howto/new-command.txt
@@ -0,0 +1,106 @@
+From: Eric S. Raymond <esr@thyrsus.com>
+Abstract: This is how-to documentation for people who want to add extension
+ commands to Git.  It should be read alongside api-builtin.txt.
+Content-type: text/asciidoc
+
+How to integrate new subcommands
+================================
+
+This is how-to documentation for people who want to add extension
+commands to Git.  It should be read alongside api-builtin.txt.
+
+Runtime environment
+-------------------
+
+Git subcommands are standalone executables that live in the Git exec
+path, normally /usr/lib/git-core.  The git executable itself is a
+thin wrapper that knows where the subcommands live, and runs them by
+passing command-line arguments to them.
+
+(If "git foo" is not found in the Git exec path, the wrapper
+will look in the rest of your $PATH for it.  Thus, it's possible
+to write local Git extensions that don't live in system space.)
+
+Implementation languages
+------------------------
+
+Most subcommands are written in C or shell.  A few are written in
+Perl.
+
+While we strongly encourage coding in portable C for portability,
+these specific scripting languages are also acceptable.  We won't
+accept more without a very strong technical case, as we don't want
+to broaden the Git suite's required dependencies.  Import utilities,
+surgical tools, remote helpers and other code at the edges of the
+Git suite are more lenient and we allow Python (and even Tcl/tk),
+but they should not be used for core functions.
+
+This may change in the future.  Especially Python is not allowed in
+core because we need better Python integration in the Git Windows
+installer before we can be confident people in that environment
+won't experience an unacceptably large loss of capability.
+
+C commands are normally written as single modules, named after the
+command, that link a collection of functions called libgit.  Thus,
+your command 'git-foo' would normally be implemented as a single
+"git-foo.c" (or "builtin/foo.c" if it is to be linked to the main
+binary); this organization makes it easy for people reading the code
+to find things.
+
+See the CodingGuidelines document for other guidance on what we consider
+good practice in C and shell, and api-builtin.txt for the support
+functions available to built-in commands written in C.
+
+What every extension command needs
+----------------------------------
+
+You must have a man page, written in asciidoc (this is what Git help
+followed by your subcommand name will display).  Be aware that there is
+a local asciidoc configuration and macros which you should use.  It's
+often helpful to start by cloning an existing page and replacing the
+text content.
+
+You must have a test, written to report in TAP (Test Anything Protocol).
+Tests are executables (usually shell scripts) that live in the 't'
+subdirectory of the tree.  Each test name begins with 't' and a sequence
+number that controls where in the test sequence it will be executed;
+conventionally the rest of the name stem is that of the command
+being tested.
+
+Read the file t/README to learn more about the conventions to be used
+in writing tests, and the test support library.
+
+Integrating a command
+---------------------
+
+Here are the things you need to do when you want to merge a new
+subcommand into the Git tree.
+
+1. Don't forget to sign off your patch!
+
+2. Append your command name to one of the variables BUILTIN_OBJS,
+EXTRA_PROGRAMS, SCRIPT_SH, SCRIPT_PERL or SCRIPT_PYTHON.
+
+3. Drop its test in the t directory.
+
+4. If your command is implemented in an interpreted language with a
+p-code intermediate form, make sure .gitignore in the main directory
+includes a pattern entry that ignores such files.  Python .pyc and
+.pyo files will already be covered.
+
+5. If your command has any dependency on a particular version of
+your language, document it in the INSTALL file.
+
+6. There is a file command-list.txt in the distribution main directory
+that categorizes commands by type, so they can be listed in appropriate
+subsections in the documentation's summary command list.  Add an entry
+for yours.  To understand the categories, look at command-list.txt
+in the main directory.  If the new command is part of the typical Git
+workflow and you believe it common enough to be mentioned in 'git help',
+map this command to a common group in the column [common].
+
+7. Give the maintainer one paragraph to include in the RelNotes file
+to describe the new feature; a good place to do so is in the cover
+letter [PATCH 0/n].
+
+That's all there is to it.
diff --git a/Documentation/howto/rebase-from-internal-branch.txt b/Documentation/howto/rebase-from-internal-branch.txt
new file mode 100644
index 000000000000..02cb5f758d6f
--- /dev/null
+++ b/Documentation/howto/rebase-from-internal-branch.txt
@@ -0,0 +1,164 @@
+From:	Junio C Hamano <gitster@pobox.com>
+To:	git@vger.kernel.org
+Cc:	Petr Baudis <pasky@suse.cz>, Linus Torvalds <torvalds@osdl.org>
+Subject: Re: sending changesets from the middle of a git tree
+Date:	Sun, 14 Aug 2005 18:37:39 -0700
+Abstract: In this article, JC talks about how he rebases the
+ public "pu" branch using the core Git tools when he updates
+ the "master" branch, and how "rebase" works.  Also discussed
+ is how this applies to individual developers who sends patches
+ upstream.
+Content-type: text/asciidoc
+
+How to rebase from an internal branch
+=====================================
+
+--------------------------------------
+Petr Baudis <pasky@suse.cz> writes:
+
+> Dear diary, on Sun, Aug 14, 2005 at 09:57:13AM CEST, I got a letter
+> where Junio C Hamano <junkio@cox.net> told me that...
+>> Linus Torvalds <torvalds@osdl.org> writes:
+>>
+>> > Junio, maybe you want to talk about how you move patches from your "pu"
+>> > branch to the real branches.
+>>
+> Actually, wouldn't this be also precisely for what StGIT is intended to?
+--------------------------------------
+
+Exactly my feeling.  I was sort of waiting for Catalin to speak
+up.  With its basing philosophical ancestry on quilt, this is
+the kind of task StGIT is designed to do.
+
+I just have done a simpler one, this time using only the core
+Git tools.
+
+I had a handful of commits that were ahead of master in pu, and I
+wanted to add some documentation bypassing my usual habit of
+placing new things in pu first.  At the beginning, the commit
+ancestry graph looked like this:
+
+                             *"pu" head
+    master --> #1 --> #2 --> #3
+
+So I started from master, made a bunch of edits, and committed:
+
+    $ git checkout master
+    $ cd Documentation; ed git.txt ...
+    $ cd ..; git add Documentation/*.txt
+    $ git commit -s
+
+After the commit, the ancestry graph would look like this:
+
+                              *"pu" head
+    master^ --> #1 --> #2 --> #3
+          \
+            \---> master
+
+The old master is now master^ (the first parent of the master).
+The new master commit holds my documentation updates.
+
+Now I have to deal with "pu" branch.
+
+This is the kind of situation I used to have all the time when
+Linus was the maintainer and I was a contributor, when you look
+at "master" branch being the "maintainer" branch, and "pu"
+branch being the "contributor" branch.  Your work started at the
+tip of the "maintainer" branch some time ago, you made a lot of
+progress in the meantime, and now the maintainer branch has some
+other commits you do not have yet.  And "git rebase" was written
+with the explicit purpose of helping to maintain branches like
+"pu".  You _could_ merge master to pu and keep going, but if you
+eventually want to cherrypick and merge some but not necessarily
+all changes back to the master branch, it often makes later
+operations for _you_ easier if you rebase (i.e. carry forward
+your changes) "pu" rather than merge.  So I ran "git rebase":
+
+    $ git checkout pu
+    $ git rebase master pu
+
+What this does is to pick all the commits since the current
+branch (note that I now am on "pu" branch) forked from the
+master branch, and forward port these changes.
+
+    master^ --> #1 --> #2 --> #3
+          \                                  *"pu" head
+            \---> master --> #1' --> #2' --> #3'
+
+The diff between master^ and #1 is applied to master and
+committed to create #1' commit with the commit information (log,
+author and date) taken from commit #1.  On top of that #2' and #3'
+commits are made similarly out of #2 and #3 commits.
+
+Old #3 is not recorded in any of the .git/refs/heads/ file
+anymore, so after doing this you will have dangling commit if
+you ran fsck-cache, which is normal.  After testing "pu", you
+can run "git prune" to get rid of those original three commits.
+
+While I am talking about "git rebase", I should talk about how
+to do cherrypicking using only the core Git tools.
+
+Let's go back to the earlier picture, with different labels.
+
+You, as an individual developer, cloned upstream repository and
+made a couple of commits on top of it.
+
+                              *your "master" head
+   upstream --> #1 --> #2 --> #3
+
+You would want changes #2 and #3 incorporated in the upstream,
+while you feel that #1 may need further improvements.  So you
+prepare #2 and #3 for e-mail submission.
+
+    $ git format-patch master^^ master
+
+This creates two files, 0001-XXXX.patch and 0002-XXXX.patch.  Send
+them out "To: " your project maintainer and "Cc: " your mailing
+list.  You could use contributed script git-send-email if
+your host has necessary perl modules for this, but your usual
+MUA would do as long as it does not corrupt whitespaces in the
+patch.
+
+Then you would wait, and you find out that the upstream picked
+up your changes, along with other changes.
+
+   where                      *your "master" head
+  upstream --> #1 --> #2 --> #3
+    used   \
+   to be     \--> #A --> #2' --> #3' --> #B --> #C
+                                                *upstream head
+
+The two commits #2' and #3' in the above picture record the same
+changes your e-mail submission for #2 and #3 contained, but
+probably with the new sign-off line added by the upstream
+maintainer and definitely with different committer and ancestry
+information, they are different objects from #2 and #3 commits.
+
+You fetch from upstream, but not merge.
+
+    $ git fetch upstream
+
+This leaves the updated upstream head in .git/FETCH_HEAD but
+does not touch your .git/HEAD or .git/refs/heads/master.
+You run "git rebase" now.
+
+    $ git rebase FETCH_HEAD master
+
+Earlier, I said that rebase applies all the commits from your
+branch on top of the upstream head.  Well, I lied.  "git rebase"
+is a bit smarter than that and notices that #2 and #3 need not
+be applied, so it only applies #1.  The commit ancestry graph
+becomes something like this:
+
+   where                     *your old "master" head
+  upstream --> #1 --> #2 --> #3
+    used   \                      your new "master" head*
+   to be     \--> #A --> #2' --> #3' --> #B --> #C --> #1'
+                                                *upstream
+                                                head
+
+Again, "git prune" would discard the disused commits #1-#3 and
+you continue on starting from the new "master" head, which is
+the #1' commit.
+
+-jc
diff --git a/Documentation/howto/rebuild-from-update-hook.txt b/Documentation/howto/rebuild-from-update-hook.txt
new file mode 100644
index 000000000000..db219f5c0745
--- /dev/null
+++ b/Documentation/howto/rebuild-from-update-hook.txt
@@ -0,0 +1,90 @@
+Subject: [HOWTO] Using post-update hook
+Message-ID: <7vy86o6usx.fsf@assigned-by-dhcp.cox.net>
+From: Junio C Hamano <gitster@pobox.com>
+Date: Fri, 26 Aug 2005 18:19:10 -0700
+Abstract: In this how-to article, JC talks about how he
+ uses the post-update hook to automate Git documentation page
+ shown at https://www.kernel.org/pub/software/scm/git/docs/.
+Content-type: text/asciidoc
+
+How to rebuild from update hook
+===============================
+
+The pages under https://www.kernel.org/pub/software/scm/git/docs/
+are built from Documentation/ directory of the git.git project
+and needed to be kept up-to-date.  The www.kernel.org/ servers
+are mirrored and I was told that the origin of the mirror is on
+the machine $some.kernel.org, on which I was given an account
+when I took over Git maintainership from Linus.
+
+The directories relevant to this how-to are these two:
+
+    /pub/scm/git/git.git/	The public Git repository.
+    /pub/software/scm/git/docs/	The HTML documentation page.
+
+So I made a repository to generate the documentation under my
+home directory over there.
+
+    $ cd
+    $ mkdir doc-git && cd doc-git
+    $ git clone /pub/scm/git/git.git/ docgen
+
+What needs to happen is to update the $HOME/doc-git/docgen/
+working tree, build HTML docs there and install the result in
+/pub/software/scm/git/docs/ directory.  So I wrote a little
+script:
+
+    $ cat >dododoc.sh <<\EOF
+    #!/bin/sh
+    cd $HOME/doc-git/docgen || exit
+
+    unset GIT_DIR
+
+    git pull /pub/scm/git/git.git/ master &&
+    cd Documentation &&
+    make install-webdoc
+    EOF
+
+Initially I used to run this by hand whenever I push into the
+public Git repository.  Then I did a cron job that ran twice a
+day.  The current round uses the post-update hook mechanism,
+like this:
+
+    $ cat >/pub/scm/git/git.git/hooks/post-update <<\EOF
+    #!/bin/sh
+    #
+    # An example hook script to prepare a packed repository for use over
+    # dumb transports.
+    #
+    # To enable this hook, make this file executable by "chmod +x post-update".
+
+    case " $* " in
+    *' refs/heads/master '*)
+            echo $HOME/doc-git/dododoc.sh | at now
+            ;;
+    esac
+    exec git-update-server-info
+    EOF
+    $ chmod +x /pub/scm/git/git.git/hooks/post-update
+
+There are four things worth mentioning:
+
+ - The update-hook is run after the repository accepts a "git
+   push", under my user privilege.  It is given the full names
+   of refs that have been updated as arguments.  My post-update
+   runs the dododoc.sh script only when the master head is
+   updated.
+
+ - When update-hook is run, GIT_DIR is set to '.' by the calling
+   receive-pack.  This is inherited by the dododoc.sh run via
+   the "at" command, and needs to be unset; otherwise, "git
+   pull" it does into $HOME/doc-git/docgen/ repository would not
+   work correctly.
+
+ - The stdout of update hook script is not connected to git
+   push; I run the heavy part of the command inside "at", to
+   receive the execution report via e-mail.
+
+ - This is still crude and does not protect against simultaneous
+   make invocations stomping on each other.  I would need to add
+   some locking mechanism for this.
diff --git a/Documentation/howto/recover-corrupted-blob-object.txt b/Documentation/howto/recover-corrupted-blob-object.txt
new file mode 100644
index 000000000000..1b3b188d3c15
--- /dev/null
+++ b/Documentation/howto/recover-corrupted-blob-object.txt
@@ -0,0 +1,144 @@
+Date: Fri, 9 Nov 2007 08:28:38 -0800 (PST)
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Subject: corrupt object on git-gc
+Abstract: Some tricks to reconstruct blob objects in order to fix
+ a corrupted repository.
+Content-type: text/asciidoc
+
+How to recover a corrupted blob object
+======================================
+
+-----------------------------------------------------------
+On Fri, 9 Nov 2007, Yossi Leybovich wrote:
+>
+> Did not help still the repository look for this object?
+> Any one know how can I track this object and understand which file is it
+-----------------------------------------------------------
+
+So exactly *because* the SHA-1 hash is cryptographically secure, the hash
+itself doesn't actually tell you anything, in order to fix a corrupt
+object you basically have to find the "original source" for it.
+
+The easiest way to do that is almost always to have backups, and find the
+same object somewhere else. Backups really are a good idea, and Git makes
+it pretty easy (if nothing else, just clone the repository somewhere else,
+and make sure that you do *not* use a hard-linked clone, and preferably
+not the same disk/machine).
+
+But since you don't seem to have backups right now, the good news is that
+especially with a single blob being corrupt, these things *are* somewhat
+debuggable.
+
+First off, move the corrupt object away, and *save* it. The most common
+cause of corruption so far has been memory corruption, but even so, there
+are people who would be interested in seeing the corruption - but it's
+basically impossible to judge the corruption until we can also see the
+original object, so right now the corrupt object is useless, but it's very
+interesting for the future, in the hope that you can re-create a
+non-corrupt version.
+
+-----------------------------------------------------------
+So:
+
+> ib]$ mv .git/objects/4b/9458b3786228369c63936db65827de3cc06200 ../
+-----------------------------------------------------------
+
+This is the right thing to do, although it's usually best to save it under
+it's full SHA-1 name (you just dropped the "4b" from the result ;).
+
+Let's see what that tells us:
+
+-----------------------------------------------------------
+> ib]$ git-fsck --full
+> broken link from    tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
+>              to    blob 4b9458b3786228369c63936db65827de3cc06200
+> missing blob 4b9458b3786228369c63936db65827de3cc06200
+-----------------------------------------------------------
+
+Ok, I removed the "dangling commit" messages, because they are just
+messages about the fact that you probably have rebased etc, so they're not
+at all interesting. But what remains is still very useful. In particular,
+we now know which tree points to it!
+
+Now you can do
+
+	git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
+
+which will show something like
+
+	100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8    .gitignore
+	100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883    .mailmap
+	100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c    COPYING
+	100644 blob ee909f2cc49e54f0799a4739d24c4cb9151ae453    CREDITS
+	040000 tree 0f5f709c17ad89e72bdbbef6ea221c69807009f6    Documentation
+	100644 blob 1570d248ad9237e4fa6e4d079336b9da62d9ba32    Kbuild
+	100644 blob 1c7c229a092665b11cd46a25dbd40feeb31661d9    MAINTAINERS
+	...
+
+and you should now have a line that looks like
+
+	10064 blob 4b9458b3786228369c63936db65827de3cc06200	my-magic-file
+
+in the output. This already tells you a *lot* it tells you what file the
+corrupt blob came from!
+
+Now, it doesn't tell you quite enough, though: it doesn't tell what
+*version* of the file didn't get correctly written! You might be really
+lucky, and it may be the version that you already have checked out in your
+working tree, in which case fixing this problem is really simple, just do
+
+	git hash-object -w my-magic-file
+
+again, and if it outputs the missing SHA-1 (4b945..) you're now all done!
+
+But that's the really lucky case, so let's assume that it was some older
+version that was broken. How do you tell which version it was?
+
+The easiest way to do it is to do
+
+	git log --raw --all --full-history -- subdirectory/my-magic-file
+
+and that will show you the whole log for that file (please realize that
+the tree you had may not be the top-level tree, so you need to figure out
+which subdirectory it was in on your own), and because you're asking for
+raw output, you'll now get something like
+
+	commit abc
+	Author:
+	Date:
+	  ..
+	:100644 100644 4b9458b... newsha... M  somedirectory/my-magic-file
+
+
+	commit xyz
+	Author:
+	Date:
+
+	  ..
+	:100644 100644 oldsha... 4b9458b... M	somedirectory/my-magic-file
+
+and this actually tells you what the *previous* and *subsequent* versions
+of that file were! So now you can look at those ("oldsha" and "newsha"
+respectively), and hopefully you have done commits often, and can
+re-create the missing my-magic-file version by looking at those older and
+newer versions!
+
+If you can do that, you can now recreate the missing object with
+
+	git hash-object -w <recreated-file>
+
+and your repository is good again!
+
+(Btw, you could have ignored the fsck, and started with doing a
+
+	git log --raw --all
+
+and just looked for the sha of the missing object (4b9458b..) in that
+whole thing. It's up to you - Git does *have* a lot of information, it is
+just missing one particular blob version.
+
+Trying to recreate trees and especially commits is *much* harder. So you
+were lucky that it's a blob. It's quite possible that you can recreate the
+thing.
+
+			Linus
diff --git a/Documentation/howto/recover-corrupted-object-harder.txt b/Documentation/howto/recover-corrupted-object-harder.txt
new file mode 100644
index 000000000000..8994e2559eac
--- /dev/null
+++ b/Documentation/howto/recover-corrupted-object-harder.txt
@@ -0,0 +1,479 @@
+Date: Wed, 16 Oct 2013 04:34:01 -0400
+From: Jeff King <peff@peff.net>
+Subject: pack corruption post-mortem
+Abstract: Recovering a corrupted object when no good copy is available.
+Content-type: text/asciidoc
+
+How to recover an object from scratch
+=====================================
+
+I was recently presented with a repository with a corrupted packfile,
+and was asked if the data was recoverable. This post-mortem describes
+the steps I took to investigate and fix the problem. I thought others
+might find the process interesting, and it might help somebody in the
+same situation.
+
+********************************
+Note: In this case, no good copy of the repository was available. For
+the much easier case where you can get the corrupted object from
+elsewhere, see link:recover-corrupted-blob-object.html[this howto].
+********************************
+
+I started with an fsck, which found a problem with exactly one object
+(I've used $pack and $obj below to keep the output readable, and also
+because I'll refer to them later):
+
+-----------
+    $ git fsck
+    error: $pack SHA1 checksum mismatch
+    error: index CRC mismatch for object $obj from $pack at offset 51653873
+    error: inflate: data stream error (incorrect data check)
+    error: cannot unpack $obj from $pack at offset 51653873
+-----------
+
+The pack checksum failing means a byte is munged somewhere, and it is
+presumably in the object mentioned (since both the index checksum and
+zlib were failing).
+
+Reading the zlib source code, I found that "incorrect data check" means
+that the adler-32 checksum at the end of the zlib data did not match the
+inflated data. So stepping the data through zlib would not help, as it
+did not fail until the very end, when we realize the CRC does not match.
+The problematic bytes could be anywhere in the object data.
+
+The first thing I did was pull the broken data out of the packfile. I
+needed to know how big the object was, which I found out with:
+
+------------
+    $ git show-index <$idx | cut -d' ' -f1 | sort -n | grep -A1 51653873
+    51653873
+    51664736
+------------
+
+Show-index gives us the list of objects and their offsets. We throw away
+everything but the offsets, and then sort them so that our interesting
+offset (which we got from the fsck output above) is followed immediately
+by the offset of the next object. Now we know that the object data is
+10863 bytes long, and we can grab it with:
+
+------------
+  dd if=$pack of=object bs=1 skip=51653873 count=10863
+------------
+
+I inspected a hexdump of the data, looking for any obvious bogosity
+(e.g., a 4K run of zeroes would be a good sign of filesystem
+corruption). But everything looked pretty reasonable.
+
+Note that the "object" file isn't fit for feeding straight to zlib; it
+has the git packed object header, which is variable-length. We want to
+strip that off so we can start playing with the zlib data directly. You
+can either work your way through it manually (the format is described in
+link:../technical/pack-format.html[Documentation/technical/pack-format.txt]),
+or you can walk through it in a debugger. I did the latter, creating a
+valid pack like:
+
+------------
+    # pack magic and version
+    printf 'PACK\0\0\0\2' >tmp.pack
+    # pack has one object
+    printf '\0\0\0\1' >>tmp.pack
+    # now add our object data
+    cat object >>tmp.pack
+    # and then append the pack trailer
+    /path/to/git.git/t/helper/test-tool sha1 -b <tmp.pack >trailer
+    cat trailer >>tmp.pack
+------------
+
+and then running "git index-pack tmp.pack" in the debugger (stop at
+unpack_raw_entry). Doing this, I found that there were 3 bytes of header
+(and the header itself had a sane type and size). So I stripped those
+off with:
+
+------------
+    dd if=object of=zlib bs=1 skip=3
+------------
+
+I ran the result through zlib's inflate using a custom C program. And
+while it did report the error, I did get the right number of output
+bytes (i.e., it matched git's size header that we decoded above). But
+feeding the result back to "git hash-object" didn't produce the same
+sha1. So there were some wrong bytes, but I didn't know which. The file
+happened to be C source code, so I hoped I could notice something
+obviously wrong with it, but I didn't. I even got it to compile!
+
+I also tried comparing it to other versions of the same path in the
+repository, hoping that there would be some part of the diff that didn't
+make sense. Unfortunately, this happened to be the only revision of this
+particular file in the repository, so I had nothing to compare against.
+
+So I took a different approach. Working under the guess that the
+corruption was limited to a single byte, I wrote a program to munge each
+byte individually, and try inflating the result. Since the object was
+only 10K compressed, that worked out to about 2.5M attempts, which took
+a few minutes.
+
+The program I used is here:
+
+----------------------------------------------
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <signal.h>
+#include <zlib.h>
+
+static int try_zlib(unsigned char *buf, int len)
+{
+	/* make this absurdly large so we don't have to loop */
+	static unsigned char out[1024*1024];
+	z_stream z;
+	int ret;
+
+	memset(&z, 0, sizeof(z));
+	inflateInit(&z);
+
+	z.next_in = buf;
+	z.avail_in = len;
+	z.next_out = out;
+	z.avail_out = sizeof(out);
+
+	ret = inflate(&z, 0);
+	inflateEnd(&z);
+	return ret >= 0;
+}
+
+/* eye candy */
+static int counter = 0;
+static void progress(int sig)
+{
+	fprintf(stderr, "\r%d", counter);
+	alarm(1);
+}
+
+int main(void)
+{
+	/* oversized so we can read the whole buffer in */
+	unsigned char buf[1024*1024];
+	int len;
+	unsigned i, j;
+
+	signal(SIGALRM, progress);
+	alarm(1);
+
+	len = read(0, buf, sizeof(buf));
+	for (i = 0; i < len; i++) {
+		unsigned char c = buf[i];
+		for (j = 0; j <= 0xff; j++) {
+			buf[i] = j;
+
+			counter++;
+			if (try_zlib(buf, len))
+				printf("i=%d, j=%x\n", i, j);
+		}
+		buf[i] = c;
+	}
+
+	alarm(0);
+	fprintf(stderr, "\n");
+	return 0;
+}
+----------------------------------------------
+
+I compiled and ran with:
+
+-------
+  gcc -Wall -Werror -O3 munge.c -o munge -lz
+  ./munge <zlib
+-------
+
+
+There were a few false positives early on (if you write "no data" in the
+zlib header, zlib thinks it's just fine :) ). But I got a hit about
+halfway through:
+
+-------
+  i=5642, j=c7
+-------
+
+I let it run to completion, and got a few more hits at the end (where it
+was munging the CRC to match our broken data). So there was a good
+chance this middle hit was the source of the problem.
+
+I confirmed by tweaking the byte in a hex editor, zlib inflating the
+result (no errors!), and then piping the output into "git hash-object",
+which reported the sha1 of the broken object. Success!
+
+I fixed the packfile itself with:
+
+-------
+  chmod +w $pack
+  printf '\xc7' | dd of=$pack bs=1 seek=51659518 conv=notrunc
+  chmod -w $pack
+-------
+
+The `\xc7` comes from the replacement byte our "munge" program found.
+The offset 51659518 is derived by taking the original object offset
+(51653873), adding the replacement offset found by "munge" (5642), and
+then adding back in the 3 bytes of git header we stripped.
+
+After that, "git fsck" ran clean.
+
+As for the corruption itself, I was lucky that it was indeed a single
+byte. In fact, it turned out to be a single bit. The byte 0xc7 was
+corrupted to 0xc5. So presumably it was caused by faulty hardware, or a
+cosmic ray.
+
+And the aborted attempt to look at the inflated output to see what was
+wrong? I could have looked forever and never found it. Here's the diff
+between what the corrupted data inflates to, versus the real data:
+
+--------------
+  -       cp = strtok (arg, "+");
+  +       cp = strtok (arg, ".");
+--------------
+
+It tweaked one byte and still ended up as valid, readable C that just
+happened to do something totally different! One takeaway is that on a
+less unlucky day, looking at the zlib output might have actually been
+helpful, as most random changes would actually break the C code.
+
+But more importantly, git's hashing and checksumming noticed a problem
+that easily could have gone undetected in another system. The result
+still compiled, but would have caused an interesting bug (that would
+have been blamed on some random commit).
+
+
+The adventure continues...
+--------------------------
+
+I ended up doing this again! Same entity, new hardware. The assumption
+at this point is that the old disk corrupted the packfile, and then the
+corruption was migrated to the new hardware (because it was done by
+rsync or similar, and no fsck was done at the time of migration).
+
+This time, the affected blob was over 20 megabytes, which was far too
+large to do a brute-force on. I followed the instructions above to
+create the `zlib` file. I then used the `inflate` program below to pull
+the corrupted data from that. Examining that output gave me a hint about
+where in the file the corruption was. But now I was working with the
+file itself, not the zlib contents. So knowing the sha1 of the object
+and the approximate area of the corruption, I used the `sha1-munge`
+program below to brute-force the correct byte.
+
+Here's the inflate program (it's essentially `gunzip` but without the
+`.gz` header processing):
+
+--------------------------
+#include <stdio.h>
+#include <string.h>
+#include <zlib.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv)
+{
+	/*
+	 * oversized so we can read the whole buffer in;
+	 * this could actually be switched to streaming
+	 * to avoid any memory limitations
+	 */
+	static unsigned char buf[25 * 1024 * 1024];
+	static unsigned char out[25 * 1024 * 1024];
+	int len;
+	z_stream z;
+	int ret;
+
+	len = read(0, buf, sizeof(buf));
+	memset(&z, 0, sizeof(z));
+	inflateInit(&z);
+
+	z.next_in = buf;
+	z.avail_in = len;
+	z.next_out = out;
+	z.avail_out = sizeof(out);
+
+	ret = inflate(&z, 0);
+	if (ret != Z_OK && ret != Z_STREAM_END)
+		fprintf(stderr, "initial inflate failed (%d)\n", ret);
+
+	fprintf(stderr, "outputting %lu bytes", z.total_out);
+	fwrite(out, 1, z.total_out, stdout);
+	return 0;
+}
+--------------------------
+
+And here is the `sha1-munge` program:
+
+--------------------------
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <signal.h>
+#include <openssl/sha.h>
+#include <stdlib.h>
+
+/* eye candy */
+static int counter = 0;
+static void progress(int sig)
+{
+	fprintf(stderr, "\r%d", counter);
+	alarm(1);
+}
+
+static const signed char hexval_table[256] = {
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 00-07 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 08-0f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 10-17 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 18-1f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 20-27 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 28-2f */
+	  0,  1,  2,  3,  4,  5,  6,  7,		/* 30-37 */
+	  8,  9, -1, -1, -1, -1, -1, -1,		/* 38-3f */
+	 -1, 10, 11, 12, 13, 14, 15, -1,		/* 40-47 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 48-4f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 50-57 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 58-5f */
+	 -1, 10, 11, 12, 13, 14, 15, -1,		/* 60-67 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 68-67 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 70-77 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 78-7f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 80-87 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 88-8f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 90-97 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 98-9f */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* a0-a7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* a8-af */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* b0-b7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* b8-bf */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* c0-c7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* c8-cf */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* d0-d7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* d8-df */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* e0-e7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* e8-ef */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* f0-f7 */
+	 -1, -1, -1, -1, -1, -1, -1, -1,		/* f8-ff */
+};
+
+static inline unsigned int hexval(unsigned char c)
+{
+return hexval_table[c];
+}
+
+static int get_sha1_hex(const char *hex, unsigned char *sha1)
+{
+	int i;
+	for (i = 0; i < 20; i++) {
+		unsigned int val;
+		/*
+		 * hex[1]=='\0' is caught when val is checked below,
+		 * but if hex[0] is NUL we have to avoid reading
+		 * past the end of the string:
+		 */
+		if (!hex[0])
+			return -1;
+		val = (hexval(hex[0]) << 4) | hexval(hex[1]);
+		if (val & ~0xff)
+			return -1;
+		*sha1++ = val;
+		hex += 2;
+	}
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	/* oversized so we can read the whole buffer in */
+	static unsigned char buf[25 * 1024 * 1024];
+	char header[32];
+	int header_len;
+	unsigned char have[20], want[20];
+	int start, len;
+	SHA_CTX orig;
+	unsigned i, j;
+
+	if (!argv[1] || get_sha1_hex(argv[1], want)) {
+		fprintf(stderr, "usage: sha1-munge <sha1> [start] <file.in\n");
+		return 1;
+	}
+
+	if (argv[2])
+		start = atoi(argv[2]);
+	else
+		start = 0;
+
+	len = read(0, buf, sizeof(buf));
+	header_len = sprintf(header, "blob %d", len) + 1;
+	fprintf(stderr, "using header: %s\n", header);
+
+	/*
+	 * We keep a running sha1 so that if you are munging
+	 * near the end of the file, we do not have to re-sha1
+	 * the unchanged earlier bytes
+	 */
+	SHA1_Init(&orig);
+	SHA1_Update(&orig, header, header_len);
+	if (start)
+		SHA1_Update(&orig, buf, start);
+
+	signal(SIGALRM, progress);
+	alarm(1);
+
+	for (i = start; i < len; i++) {
+		unsigned char c;
+		SHA_CTX x;
+
+#if 0
+		/*
+		 * deletion -- this would not actually work in practice,
+		 * I think, because we've already committed to a
+		 * particular size in the header. Ditto for addition
+		 * below. In those cases, you'd have to do the whole
+		 * sha1 from scratch, or possibly keep three running
+		 * "orig" sha1 computations going.
+		 */
+		memcpy(&x, &orig, sizeof(x));
+		SHA1_Update(&x, buf + i + 1, len - i - 1);
+		SHA1_Final(have, &x);
+		if (!memcmp(have, want, 20))
+			printf("i=%d, deletion\n", i);
+#endif
+
+		/*
+		 * replacement -- note that this tries each of the 256
+		 * possible bytes. If you suspect a single-bit flip,
+		 * it would be much shorter to just try the 8
+		 * bit-flipped variants.
+		 */
+		c = buf[i];
+		for (j = 0; j <= 0xff; j++) {
+			buf[i] = j;
+
+			memcpy(&x, &orig, sizeof(x));
+			SHA1_Update(&x, buf + i, len - i);
+			SHA1_Final(have, &x);
+			if (!memcmp(have, want, 20))
+				printf("i=%d, j=%02x\n", i, j);
+		}
+		buf[i] = c;
+
+#if 0
+		/* addition */
+		for (j = 0; j <= 0xff; j++) {
+			unsigned char extra = j;
+			memcpy(&x, &orig, sizeof(x));
+			SHA1_Update(&x, &extra, 1);
+			SHA1_Update(&x, buf + i, len - i);
+			SHA1_Final(have, &x);
+			if (!memcmp(have, want, 20))
+				printf("i=%d, addition=%02x", i, j);
+		}
+#endif
+
+		SHA1_Update(&orig, buf + i, 1);
+		counter++;
+	}
+
+	alarm(0);
+	fprintf(stderr, "\r%d\n", counter);
+	return 0;
+}
+--------------------------
diff --git a/Documentation/howto/revert-a-faulty-merge.txt b/Documentation/howto/revert-a-faulty-merge.txt
new file mode 100644
index 000000000000..19f59cc88808
--- /dev/null
+++ b/Documentation/howto/revert-a-faulty-merge.txt
@@ -0,0 +1,273 @@
+Date: Fri, 19 Dec 2008 00:45:19 -0800
+From: Linus Torvalds <torvalds@linux-foundation.org>, Junio C Hamano <gitster@pobox.com>
+Subject: Re: Odd merge behaviour involving reverts
+Abstract: Sometimes a branch that was already merged to the mainline
+ is later found to be faulty.  Linus and Junio give guidance on
+ recovering from such a premature merge and continuing development
+ after the offending branch is fixed.
+Message-ID: <7vocz8a6zk.fsf@gitster.siamese.dyndns.org>
+References: <alpine.LFD.2.00.0812181949450.14014@localhost.localdomain>
+Content-type: text/asciidoc
+
+How to revert a faulty merge
+============================
+
+Alan <alan@clueserver.org> said:
+
+    I have a master branch.  We have a branch off of that that some
+    developers are doing work on.  They claim it is ready. We merge it
+    into the master branch.  It breaks something so we revert the merge.
+    They make changes to the code.  they get it to a point where they say
+    it is ok and we merge again.
+
+    When examined, we find that code changes made before the revert are
+    not in the master branch, but code changes after are in the master
+    branch.
+
+and asked for help recovering from this situation.
+
+The history immediately after the "revert of the merge" would look like
+this:
+
+ ---o---o---o---M---x---x---W
+               /
+       ---A---B
+
+where A and B are on the side development that was not so good, M is the
+merge that brings these premature changes into the mainline, x are changes
+unrelated to what the side branch did and already made on the mainline,
+and W is the "revert of the merge M" (doesn't W look M upside down?).
+IOW, `"diff W^..W"` is similar to `"diff -R M^..M"`.
+
+Such a "revert" of a merge can be made with:
+
+    $ git revert -m 1 M
+
+After the developers of the side branch fix their mistakes, the history
+may look like this:
+
+ ---o---o---o---M---x---x---W---x
+               /
+       ---A---B-------------------C---D
+
+where C and D are to fix what was broken in A and B, and you may already
+have some other changes on the mainline after W.
+
+If you merge the updated side branch (with D at its tip), none of the
+changes made in A or B will be in the result, because they were reverted
+by W.  That is what Alan saw.
+
+Linus explains the situation:
+
+    Reverting a regular commit just effectively undoes what that commit
+    did, and is fairly straightforward. But reverting a merge commit also
+    undoes the _data_ that the commit changed, but it does absolutely
+    nothing to the effects on _history_ that the merge had.
+
+    So the merge will still exist, and it will still be seen as joining
+    the two branches together, and future merges will see that merge as
+    the last shared state - and the revert that reverted the merge brought
+    in will not affect that at all.
+
+    So a "revert" undoes the data changes, but it's very much _not_ an
+    "undo" in the sense that it doesn't undo the effects of a commit on
+    the repository history.
+
+    So if you think of "revert" as "undo", then you're going to always
+    miss this part of reverts. Yes, it undoes the data, but no, it doesn't
+    undo history.
+
+In such a situation, you would want to first revert the previous revert,
+which would make the history look like this:
+
+ ---o---o---o---M---x---x---W---x---Y
+               /
+       ---A---B-------------------C---D
+
+where Y is the revert of W.  Such a "revert of the revert" can be done
+with:
+
+    $ git revert W
+
+This history would (ignoring possible conflicts between what W and W..Y
+changed) be equivalent to not having W or Y at all in the history:
+
+ ---o---o---o---M---x---x-------x----
+               /
+       ---A---B-------------------C---D
+
+and merging the side branch again will not have conflict arising from an
+earlier revert and revert of the revert.
+
+ ---o---o---o---M---x---x-------x-------*
+               /                       /
+       ---A---B-------------------C---D
+
+Of course the changes made in C and D still can conflict with what was
+done by any of the x, but that is just a normal merge conflict.
+
+On the other hand, if the developers of the side branch discarded their
+faulty A and B, and redone the changes on top of the updated mainline
+after the revert, the history would have looked like this:
+
+ ---o---o---o---M---x---x---W---x---x
+               /                 \
+       ---A---B                   A'--B'--C'
+
+If you reverted the revert in such a case as in the previous example:
+
+ ---o---o---o---M---x---x---W---x---x---Y---*
+               /                 \         /
+       ---A---B                   A'--B'--C'
+
+where Y is the revert of W, A' and B' are rerolled A and B, and there may
+also be a further fix-up C' on the side branch.  `"diff Y^..Y"` is similar
+to `"diff -R W^..W"` (which in turn means it is similar to `"diff M^..M"`),
+and `"diff A'^..C'"` by definition would be similar but different from that,
+because it is a rerolled series of the earlier change.  There will be a
+lot of overlapping changes that result in conflicts.  So do not do "revert
+of revert" blindly without thinking..
+
+ ---o---o---o---M---x---x---W---x---x
+               /                 \
+       ---A---B                   A'--B'--C'
+
+In the history with rebased side branch, W (and M) are behind the merge
+base of the updated branch and the tip of the mainline, and they should
+merge without the past faulty merge and its revert getting in the way.
+
+To recap, these are two very different scenarios, and they want two very
+different resolution strategies:
+
+ - If the faulty side branch was fixed by adding corrections on top, then
+   doing a revert of the previous revert would be the right thing to do.
+
+ - If the faulty side branch whose effects were discarded by an earlier
+   revert of a merge was rebuilt from scratch (i.e. rebasing and fixing,
+   as you seem to have interpreted), then re-merging the result without
+   doing anything else fancy would be the right thing to do.
+   (See the ADDENDUM below for how to rebuild a branch from scratch
+   without changing its original branching-off point.)
+
+However, there are things to keep in mind when reverting a merge (and
+reverting such a revert).
+
+For example, think about what reverting a merge (and then reverting the
+revert) does to bisectability. Ignore the fact that the revert of a revert
+is undoing it - just think of it as a "single commit that does a lot".
+Because that is what it does.
+
+When you have a problem you are chasing down, and you hit a "revert this
+merge", what you're hitting is essentially a single commit that contains
+all the changes (but obviously in reverse) of all the commits that got
+merged. So it's debugging hell, because now you don't have lots of small
+changes that you can try to pinpoint which _part_ of it changes.
+
+But does it all work? Sure it does. You can revert a merge, and from a
+purely technical angle, Git did it very naturally and had no real
+troubles. It just considered it a change from "state before merge" to
+"state after merge", and that was it. Nothing complicated, nothing odd,
+nothing really dangerous. Git will do it without even thinking about it.
+
+So from a technical angle, there's nothing wrong with reverting a merge,
+but from a workflow angle it's something that you generally should try to
+avoid.
+
+If at all possible, for example, if you find a problem that got merged
+into the main tree, rather than revert the merge, try _really_ hard to
+bisect the problem down into the branch you merged, and just fix it, or
+try to revert the individual commit that caused it.
+
+Yes, it's more complex, and no, it's not always going to work (sometimes
+the answer is: "oops, I really shouldn't have merged it, because it wasn't
+ready yet, and I really need to undo _all_ of the merge"). So then you
+really should revert the merge, but when you want to re-do the merge, you
+now need to do it by reverting the revert.
+
+ADDENDUM
+
+Sometimes you have to rewrite one of a topic branch's commits *and* you can't
+change the topic's branching-off point.  Consider the following situation:
+
+ P---o---o---M---x---x---W---x
+  \         /
+   A---B---C
+
+where commit W reverted commit M because it turned out that commit B was wrong
+and needs to be rewritten, but you need the rewritten topic to still branch
+from commit P (perhaps P is a branching-off point for yet another branch, and
+you want be able to merge the topic into both branches).
+
+The natural thing to do in this case is to checkout the A-B-C branch and use
+"rebase -i P" to change commit B.  However this does not rewrite commit A,
+because "rebase -i" by default fast-forwards over any initial commits selected
+with the "pick" command.  So you end up with this:
+
+ P---o---o---M---x---x---W---x
+  \         /
+   A---B---C   <-- old branch
+    \
+     B'---C'   <-- naively rewritten branch
+
+To merge A-B'-C' into the mainline branch you would still have to first revert
+commit W in order to pick up the changes in A, but then it's likely that the
+changes in B' will conflict with the original B changes re-introduced by the
+reversion of W.
+
+However, you can avoid these problems if you recreate the entire branch,
+including commit A:
+
+   A'---B'---C'  <-- completely rewritten branch
+  /
+ P---o---o---M---x---x---W---x
+  \         /
+   A---B---C
+
+You can merge A'-B'-C' into the mainline branch without worrying about first
+reverting W.  Mainline's history would look like this:
+
+   A'---B'---C'------------------
+  /                              \
+ P---o---o---M---x---x---W---x---M2
+  \         /
+   A---B---C
+
+But if you don't actually need to change commit A, then you need some way to
+recreate it as a new commit with the same changes in it.  The rebase command's
+--no-ff option provides a way to do this:
+
+    $ git rebase [-i] --no-ff P
+
+The --no-ff option creates a new branch A'-B'-C' with all-new commits (all the
+SHA IDs will be different) even if in the interactive case you only actually
+modify commit B.  You can then merge this new branch directly into the mainline
+branch and be sure you'll get all of the branch's changes.
+
+You can also use --no-ff in cases where you just add extra commits to the topic
+to fix it up.  Let's revisit the situation discussed at the start of this howto:
+
+ P---o---o---M---x---x---W---x
+  \         /
+   A---B---C----------------D---E   <-- fixed-up topic branch
+
+At this point, you can use --no-ff to recreate the topic branch:
+
+    $ git checkout E
+    $ git rebase --no-ff P
+
+yielding
+
+   A'---B'---C'------------D'---E'  <-- recreated topic branch
+  /
+ P---o---o---M---x---x---W---x
+  \         /
+   A---B---C----------------D---E
+
+You can merge the recreated branch into the mainline without reverting commit W,
+and mainline's history will look like this:
+
+   A'---B'---C'------------D'---E'
+  /                              \
+ P---o---o---M---x---x---W---x---M2
+  \         /
+   A---B---C
diff --git a/Documentation/howto/revert-branch-rebase.txt b/Documentation/howto/revert-branch-rebase.txt
new file mode 100644
index 000000000000..149508e13bda
--- /dev/null
+++ b/Documentation/howto/revert-branch-rebase.txt
@@ -0,0 +1,187 @@
+From: Junio C Hamano <gitster@pobox.com>
+To: git@vger.kernel.org
+Subject: [HOWTO] Reverting an existing commit
+Abstract: In this article, JC gives a small real-life example of using
+ 'git revert' command, and using a temporary branch and tag for safety
+ and easier sanity checking.
+Date: Mon, 29 Aug 2005 21:39:02 -0700
+Content-type: text/asciidoc
+Message-ID: <7voe7g3uop.fsf@assigned-by-dhcp.cox.net>
+
+How to revert an existing commit
+================================
+
+One of the changes I pulled into the 'master' branch turns out to
+break building Git with GCC 2.95.  While they were well-intentioned
+portability fixes, keeping things working with gcc-2.95 was also
+important.  Here is what I did to revert the change in the 'master'
+branch and to adjust the 'pu' branch, using core Git tools and
+barebone Porcelain.
+
+First, prepare a throw-away branch in case I screw things up.
+
+------------------------------------------------
+$ git checkout -b revert-c99 master
+------------------------------------------------
+
+Now I am on the 'revert-c99' branch.  Let's figure out which commit to
+revert.  I happen to know that the top of the 'master' branch is a
+merge, and its second parent (i.e. foreign commit I merged from) has
+the change I would want to undo.  Further I happen to know that that
+merge introduced 5 commits or so:
+
+------------------------------------------------
+$ git show-branch --more=4 master master^2 | head
+* [master] Merge refs/heads/portable from http://www.cs.berkeley....
+ ! [master^2] Replace C99 array initializers with code.
+--
+-  [master] Merge refs/heads/portable from http://www.cs.berkeley....
+*+ [master^2] Replace C99 array initializers with code.
+*+ [master^2~1] Replace unsetenv() and setenv() with older putenv().
+*+ [master^2~2] Include sys/time.h in daemon.c.
+*+ [master^2~3] Fix ?: statements.
+*+ [master^2~4] Replace zero-length array decls with [].
+*  [master~1] tutorial note about git branch
+------------------------------------------------
+
+The '--more=4' above means "after we reach the merge base of refs,
+show until we display four more common commits".  That last commit
+would have been where the "portable" branch was forked from the main
+git.git repository, so this would show everything on both branches
+since then.  I just limited the output to the first handful using
+'head'.
+
+Now I know 'master^2~4' (pronounce it as "find the second parent of
+the 'master', and then go four generations back following the first
+parent") is the one I would want to revert.  Since I also want to say
+why I am reverting it, the '-n' flag is given to 'git revert'.  This
+prevents it from actually making a commit, and instead 'git revert'
+leaves the commit log message it wanted to use in '.msg' file:
+
+------------------------------------------------
+$ git revert -n master^2~4
+$ cat .msg
+Revert "Replace zero-length array decls with []."
+
+This reverts 6c5f9baa3bc0d63e141e0afc23110205379905a4 commit.
+$ git diff HEAD ;# to make sure what we are reverting makes sense.
+$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage.
+$ make clean test ;# make sure it did not cause other breakage.
+------------------------------------------------
+
+The reverted change makes sense (from reading the 'diff' output), does
+fix the problem (from 'make CC=gcc-2.95' test), and does not cause new
+breakage (from the last 'make test').  I'm ready to commit:
+
+------------------------------------------------
+$ git commit -a -s ;# read .msg into the log,
+                    # and explain why I am reverting.
+------------------------------------------------
+
+I could have screwed up in any of the above steps, but in the worst
+case I could just have done 'git checkout master' to start over.
+Fortunately I did not have to; what I have in the current branch
+'revert-c99' is what I want.  So merge that back into 'master':
+
+------------------------------------------------
+$ git checkout master
+$ git merge revert-c99 ;# this should be a fast-forward
+Updating from 10d781b9caa4f71495c7b34963bef137216f86a8 to e3a693c...
+ cache.h        |    8 ++++----
+ commit.c       |    2 +-
+ ls-files.c     |    2 +-
+ receive-pack.c |    2 +-
+ server-info.c  |    2 +-
+ 5 files changed, 8 insertions(+), 8 deletions(-)
+------------------------------------------------
+
+There is no need to redo the test at this point.  We fast-forwarded
+and we know 'master' matches 'revert-c99' exactly.  In fact:
+
+------------------------------------------------
+$ git diff master..revert-c99
+------------------------------------------------
+
+says nothing.
+
+Then we rebase the 'pu' branch as usual.
+
+------------------------------------------------
+$ git checkout pu
+$ git tag pu-anchor pu
+$ git rebase master
+* Applying: Redo "revert" using three-way merge machinery.
+First trying simple merge strategy to cherry-pick.
+* Applying: Remove git-apply-patch-script.
+First trying simple merge strategy to cherry-pick.
+Simple cherry-pick fails; trying Automatic cherry-pick.
+Removing Documentation/git-apply-patch-script.txt
+Removing git-apply-patch-script
+* Applying: Document "git cherry-pick" and "git revert"
+First trying simple merge strategy to cherry-pick.
+* Applying: mailinfo and applymbox updates
+First trying simple merge strategy to cherry-pick.
+* Applying: Show commits in topo order and name all commits.
+First trying simple merge strategy to cherry-pick.
+* Applying: More documentation updates.
+First trying simple merge strategy to cherry-pick.
+------------------------------------------------
+
+The temporary tag 'pu-anchor' is me just being careful, in case 'git
+rebase' screws up.  After this, I can do these for sanity check:
+
+------------------------------------------------
+$ git diff pu-anchor..pu ;# make sure we got the master fix.
+$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage.
+$ make clean test ;# make sure it did not cause other breakage.
+------------------------------------------------
+
+Everything is in the good order.  I do not need the temporary branch
+or tag anymore, so remove them:
+
+------------------------------------------------
+$ rm -f .git/refs/tags/pu-anchor
+$ git branch -d revert-c99
+------------------------------------------------
+
+It was an emergency fix, so we might as well merge it into the
+'release candidate' branch, although I expect the next release would
+be some days off:
+
+------------------------------------------------
+$ git checkout rc
+$ git pull . master
+Packing 0 objects
+Unpacking 0 objects
+
+* commit-ish: e3a693c...	refs/heads/master from .
+Trying to merge e3a693c... into 8c1f5f0... using 10d781b...
+Committed merge 7fb9b7262a1d1e0a47bbfdcbbcf50ce0635d3f8f
+ cache.h        |    8 ++++----
+ commit.c       |    2 +-
+ ls-files.c     |    2 +-
+ receive-pack.c |    2 +-
+ server-info.c  |    2 +-
+ 5 files changed, 8 insertions(+), 8 deletions(-)
+------------------------------------------------
+
+And the final repository status looks like this:
+
+------------------------------------------------
+$ git show-branch --more=1 master pu rc
+! [master] Revert "Replace zero-length array decls with []."
+ ! [pu] git-repack: Add option to repack all objects.
+  * [rc] Merge refs/heads/master from .
+---
+ +  [pu] git-repack: Add option to repack all objects.
+ +  [pu~1] More documentation updates.
+ +  [pu~2] Show commits in topo order and name all commits.
+ +  [pu~3] mailinfo and applymbox updates
+ +  [pu~4] Document "git cherry-pick" and "git revert"
+ +  [pu~5] Remove git-apply-patch-script.
+ +  [pu~6] Redo "revert" using three-way merge machinery.
+  - [rc] Merge refs/heads/master from .
+++* [master] Revert "Replace zero-length array decls with []."
+  - [rc~1] Merge refs/heads/master from .
+... [master~1] Merge refs/heads/portable from http://www.cs.berkeley....
+------------------------------------------------
diff --git a/Documentation/howto/separating-topic-branches.txt b/Documentation/howto/separating-topic-branches.txt
new file mode 100644
index 000000000000..bd1027433bb7
--- /dev/null
+++ b/Documentation/howto/separating-topic-branches.txt
@@ -0,0 +1,94 @@
+From: Junio C Hamano <gitster@pobox.com>
+Subject: Separating topic branches
+Abstract: In this article, JC describes how to separate topic branches.
+Content-type: text/asciidoc
+
+How to separate topic branches
+==============================
+
+This text was originally a footnote to a discussion about the
+behaviour of the git diff commands.
+
+Often I find myself doing that [running diff against something other
+than HEAD] while rewriting messy development history.  For example, I
+start doing some work without knowing exactly where it leads, and end
+up with a history like this:
+
+            "master"
+        o---o
+             \                    "topic"
+              o---o---o---o---o---o
+
+At this point, "topic" contains something I know I want, but it
+contains two concepts that turned out to be completely independent.
+And often, one topic component is larger than the other.  It may
+contain more than two topics.
+
+In order to rewrite this mess to be more manageable, I would first do
+"diff master..topic", to extract the changes into a single patch, start
+picking pieces from it to get logically self-contained units, and
+start building on top of "master":
+
+        $ git diff master..topic >P.diff
+        $ git checkout -b topicA master
+        ... pick and apply pieces from P.diff to build
+        ... commits on topicA branch.
+
+              o---o---o
+             /        "topicA"
+        o---o"master"
+             \                    "topic"
+              o---o---o---o---o---o
+
+Before doing each commit on "topicA" HEAD, I run "diff HEAD"
+before update-index the affected paths, or "diff --cached HEAD"
+after.  Also I would run "diff --cached master" to make sure
+that the changes are only the ones related to "topicA".  Usually
+I do this for smaller topics first.
+
+After that, I'd do the remainder of the original "topic", but
+for that, I do not start from the patchfile I extracted by
+comparing "master" and "topic" I used initially.  Still on
+"topicA", I extract "diff topic", and use it to rebuild the
+other topic:
+
+        $ git diff -R topic >P.diff ;# --cached also would work fine
+        $ git checkout -b topicB master
+        ... pick and apply pieces from P.diff to build
+        ... commits on topicB branch.
+
+                                "topicB"
+               o---o---o---o---o
+              /
+             /o---o---o
+            |/        "topicA"
+        o---o"master"
+             \                    "topic"
+              o---o---o---o---o---o
+
+After I am done, I'd try a pretend-merge between "topicA" and
+"topicB" in order to make sure I have not missed anything:
+
+        $ git pull . topicA ;# merge it into current "topicB"
+        $ git diff topic
+                                "topicB"
+               o---o---o---o---o---* (pretend merge)
+              /                   /
+             /o---o---o----------'
+            |/        "topicA"
+        o---o"master"
+             \                    "topic"
+              o---o---o---o---o---o
+
+The last diff better not to show anything other than cleanups
+for crufts.  Then I can finally clean things up:
+
+        $ git branch -D topic
+        $ git reset --hard HEAD^ ;# nuke pretend merge
+
+                                "topicB"
+               o---o---o---o---o
+              /
+             /o---o---o
+            |/        "topicA"
+        o---o"master"
diff --git a/Documentation/howto/setup-git-server-over-http.txt b/Documentation/howto/setup-git-server-over-http.txt
new file mode 100644
index 000000000000..bfe6f9b50063
--- /dev/null
+++ b/Documentation/howto/setup-git-server-over-http.txt
@@ -0,0 +1,285 @@
+From: Rutger Nijlunsing <rutger@nospam.com>
+Subject: Setting up a Git repository which can be pushed into and pulled from over HTTP(S).
+Date: Thu, 10 Aug 2006 22:00:26 +0200
+Content-type: text/asciidoc
+
+How to setup Git server over http
+=================================
+
+NOTE: This document is from 2006.  A lot has happened since then, and this
+document is now relevant mainly if your web host is not CGI capable.
+Almost everyone else should instead look at linkgit:git-http-backend[1].
+
+Since Apache is one of those packages people like to compile
+themselves while others prefer the bureaucrat's dream Debian, it is
+impossible to give guidelines which will work for everyone. Just send
+some feedback to the mailing list at git@vger.kernel.org to get this
+document tailored to your favorite distro.
+
+
+What's needed:
+
+- Have an Apache web-server
+
+  On Debian:
+    $ apt-get install apache2
+    To get apache2 by default started,
+    edit /etc/default/apache2 and set NO_START=0
+
+- can edit the configuration of it.
+
+  This could be found under /etc/httpd, or refer to your Apache documentation.
+
+  On Debian: this means being able to edit files under /etc/apache2
+
+- can restart it.
+
+  'apachectl --graceful' might do. If it doesn't, just stop and
+  restart apache. Be warning that active connections to your server
+  might be aborted by this.
+
+  On Debian:
+    $ /etc/init.d/apache2 restart
+  or
+    $ /etc/init.d/apache2 force-reload
+    (which seems to do the same)
+  This adds symlinks from the /etc/apache2/mods-enabled to
+  /etc/apache2/mods-available.
+
+- have permissions to chown a directory
+
+- have Git installed on the client, and
+
+- either have Git installed on the server or have a webdav client on
+  the client.
+
+In effect, this means you're going to be root, or that you're using a
+preconfigured WebDAV server.
+
+
+Step 1: setup a bare Git repository
+-----------------------------------
+
+At the time of writing, git-http-push cannot remotely create a Git
+repository. So we have to do that at the server side with Git. Another
+option is to generate an empty bare repository at the client and copy
+it to the server with a WebDAV client (which is the only option if Git
+is not installed on the server).
+
+Create the directory under the DocumentRoot of the directories served
+by Apache. As an example we take /usr/local/apache2, but try "grep
+DocumentRoot /where/ever/httpd.conf" to find your root:
+
+    $ cd /usr/local/apache/htdocs
+    $ mkdir my-new-repo.git
+
+  On Debian:
+
+    $ cd /var/www
+    $ mkdir my-new-repo.git
+
+
+Initialize a bare repository
+
+    $ cd my-new-repo.git
+    $ git --bare init
+
+
+Change the ownership to your web-server's credentials. Use `"grep ^User
+httpd.conf"` and `"grep ^Group httpd.conf"` to find out:
+
+    $ chown -R www.www .
+
+  On Debian:
+
+    $ chown -R www-data.www-data .
+
+
+If you do not know which user Apache runs as, you can alternatively do
+a "chmod -R a+w .", inspect the files which are created later on, and
+set the permissions appropriately.
+
+Restart apache2, and check whether http://server/my-new-repo.git gives
+a directory listing. If not, check whether apache started up
+successfully.
+
+
+Step 2: enable DAV on this repository
+-------------------------------------
+
+First make sure the dav_module is loaded. For this, insert in httpd.conf:
+
+    LoadModule dav_module libexec/httpd/libdav.so
+    AddModule mod_dav.c
+
+Also make sure that this line exists which is the file used for
+locking DAV operations:
+
+  DAVLockDB "/usr/local/apache2/temp/DAV.lock"
+
+  On Debian these steps can be performed with:
+
+    Enable the dav and dav_fs modules of apache:
+    $ a2enmod dav_fs
+    (just to be sure. dav_fs might be unneeded, I don't know)
+    $ a2enmod dav
+    The DAV lock is located in /etc/apache2/mods-available/dav_fs.conf:
+      DAVLockDB /var/lock/apache2/DAVLock
+
+Of course, it can point somewhere else, but the string is actually just a
+prefix in some Apache configurations, and therefore the _directory_ has to
+be writable by the user Apache runs as.
+
+Then, add something like this to your httpd.conf
+
+  <Location /my-new-repo.git>
+     DAV on
+     AuthType Basic
+     AuthName "Git"
+     AuthUserFile /usr/local/apache2/conf/passwd.git
+     Require valid-user
+  </Location>
+
+  On Debian:
+    Create (or add to) /etc/apache2/conf.d/git.conf :
+
+    <Location /my-new-repo.git>
+       DAV on
+       AuthType Basic
+       AuthName "Git"
+       AuthUserFile /etc/apache2/passwd.git
+       Require valid-user
+    </Location>
+
+    Debian automatically reads all files under /etc/apache2/conf.d.
+
+The password file can be somewhere else, but it has to be readable by
+Apache and preferably not readable by the world.
+
+Create this file by
+    $ htpasswd -c /usr/local/apache2/conf/passwd.git <user>
+
+    On Debian:
+      $ htpasswd -c /etc/apache2/passwd.git <user>
+
+You will be asked a password, and the file is created. Subsequent calls
+to htpasswd should omit the '-c' option, since you want to append to the
+existing file.
+
+You need to restart Apache.
+
+Now go to http://<username>@<servername>/my-new-repo.git in your
+browser to check whether it asks for a password and accepts the right
+password.
+
+On Debian:
+
+   To test the WebDAV part, do:
+
+   $ apt-get install litmus
+   $ litmus http://<servername>/my-new-repo.git <username> <password>
+
+   Most tests should pass.
+
+A command-line tool to test WebDAV is cadaver. If you prefer GUIs, for
+example, konqueror can open WebDAV URLs as "webdav://..." or
+"webdavs://...".
+
+If you're into Windows, from XP onwards Internet Explorer supports
+WebDAV. For this, do Internet Explorer -> Open Location ->
+http://<servername>/my-new-repo.git [x] Open as webfolder -> login .
+
+
+Step 3: setup the client
+------------------------
+
+Make sure that you have HTTP support, i.e. your Git was built with
+libcurl (version more recent than 7.10). The command 'git http-push' with
+no argument should display a usage message.
+
+Then, add the following to your $HOME/.netrc (you can do without, but will be
+asked to input your password a _lot_ of times):
+
+    machine <servername>
+    login <username>
+    password <password>
+
+...and set permissions:
+     chmod 600 ~/.netrc
+
+If you want to access the web-server by its IP, you have to type that in,
+instead of the server name.
+
+To check whether all is OK, do:
+
+   curl --netrc --location -v http://<username>@<servername>/my-new-repo.git/HEAD
+
+...this should give something like 'ref: refs/heads/master', which is
+the content of the file HEAD on the server.
+
+Now, add the remote in your existing repository which contains the project
+you want to export:
+
+   $ git-config remote.upload.url \
+       http://<username>@<servername>/my-new-repo.git/
+
+It is important to put the last '/'; Without it, the server will send
+a redirect which git-http-push does not (yet) understand, and git-http-push
+will repeat the request infinitely.
+
+
+Step 4: make the initial push
+-----------------------------
+
+From your client repository, do
+
+   $ git push upload master
+
+This pushes branch 'master' (which is assumed to be the branch you
+want to export) to repository called 'upload', which we previously
+defined with git-config.
+
+
+Using a proxy:
+--------------
+
+If you have to access the WebDAV server from behind an HTTP(S) proxy,
+set the variable 'all_proxy' to `http://proxy-host.com:port`, or
+`http://login-on-proxy:passwd-on-proxy@proxy-host.com:port`. See 'man
+curl' for details.
+
+
+Troubleshooting:
+----------------
+
+If git-http-push says
+
+   Error: no DAV locking support on remote repo http://...
+
+then it means the web-server did not accept your authentication. Make sure
+that the user name and password matches in httpd.conf, .netrc and the URL
+you are uploading to.
+
+If git-http-push shows you an error (22/502) when trying to MOVE a blob,
+it means that your web-server somehow does not recognize its name in the
+request; This can happen when you start Apache, but then disable the
+network interface. A simple restart of Apache helps.
+
+Errors like (22/502) are of format (curl error code/http error
+code). So (22/404) means something like 'not found' at the server.
+
+Reading /usr/local/apache2/logs/error_log is often helpful.
+
+  On Debian: Read /var/log/apache2/error.log instead.
+
+If you access HTTPS locations, Git may fail verifying the SSL
+certificate (this is return code 60). Setting http.sslVerify=false can
+help diagnosing the problem, but removes security checks.
+
+
+Debian References: http://www.debian-administration.org/articles/285
+
+Authors
+  Johannes Schindelin <Johannes.Schindelin@gmx.de>
+  Rutger Nijlunsing <git@wingding.demon.nl>
+  Matthieu Moy <Matthieu.Moy@imag.fr>
diff --git a/Documentation/howto/update-hook-example.txt b/Documentation/howto/update-hook-example.txt
new file mode 100644
index 000000000000..89821ec74fe1
--- /dev/null
+++ b/Documentation/howto/update-hook-example.txt
@@ -0,0 +1,192 @@
+From: Junio C Hamano <gitster@pobox.com> and Carl Baldwin <cnb@fc.hp.com>
+Subject: control access to branches.
+Date: Thu, 17 Nov 2005 23:55:32 -0800
+Message-ID: <7vfypumlu3.fsf@assigned-by-dhcp.cox.net>
+Abstract: An example hooks/update script is presented to
+ implement repository maintenance policies, such as who can push
+ into which branch and who can make a tag.
+Content-type: text/asciidoc
+
+How to use the update hook
+==========================
+
+When your developer runs git-push into the repository,
+git-receive-pack is run (either locally or over ssh) as that
+developer, so is hooks/update script.  Quoting from the relevant
+section of the documentation:
+
+    Before each ref is updated, if $GIT_DIR/hooks/update file exists
+    and executable, it is called with three parameters:
+
+           $GIT_DIR/hooks/update refname sha1-old sha1-new
+
+    The refname parameter is relative to $GIT_DIR; e.g. for the
+    master head this is "refs/heads/master".  Two sha1 are the
+    object names for the refname before and after the update.  Note
+    that the hook is called before the refname is updated, so either
+    sha1-old is 0{40} (meaning there is no such ref yet), or it
+    should match what is recorded in refname.
+
+So if your policy is (1) always require fast-forward push
+(i.e. never allow "git-push repo +branch:branch"), (2) you
+have a list of users allowed to update each branch, and (3) you
+do not let tags to be overwritten, then you can use something
+like this as your hooks/update script.
+
+[jc: editorial note.  This is a much improved version by Carl
+since I posted the original outline]
+
+----------------------------------------------------
+#!/bin/bash
+
+umask 002
+
+# If you are having trouble with this access control hook script
+# you can try setting this to true.  It will tell you exactly
+# why a user is being allowed/denied access.
+
+verbose=false
+
+# Default shell globbing messes things up downstream
+GLOBIGNORE=*
+
+function grant {
+  $verbose && echo >&2 "-Grant-		$1"
+  echo grant
+  exit 0
+}
+
+function deny {
+  $verbose && echo >&2 "-Deny-		$1"
+  echo deny
+  exit 1
+}
+
+function info {
+  $verbose && echo >&2 "-Info-		$1"
+}
+
+# Implement generic branch and tag policies.
+# - Tags should not be updated once created.
+# - Branches should only be fast-forwarded unless their pattern starts with '+'
+case "$1" in
+  refs/tags/*)
+    git rev-parse --verify -q "$1" &&
+    deny >/dev/null "You can't overwrite an existing tag"
+    ;;
+  refs/heads/*)
+    # No rebasing or rewinding
+    if expr "$2" : '0*$' >/dev/null; then
+      info "The branch '$1' is new..."
+    else
+      # updating -- make sure it is a fast-forward
+      mb=$(git merge-base "$2" "$3")
+      case "$mb,$2" in
+        "$2,$mb") info "Update is fast-forward" ;;
+	*)	  noff=y; info "This is not a fast-forward update.";;
+      esac
+    fi
+    ;;
+  *)
+    deny >/dev/null \
+    "Branch is not under refs/heads or refs/tags.  What are you trying to do?"
+    ;;
+esac
+
+# Implement per-branch controls based on username
+allowed_users_file=$GIT_DIR/info/allowed-users
+username=$(id -u -n)
+info "The user is: '$username'"
+
+if test -f "$allowed_users_file"
+then
+  rc=$(cat $allowed_users_file | grep -v '^#' | grep -v '^$' |
+    while read heads user_patterns
+    do
+      # does this rule apply to us?
+      head_pattern=${heads#+}
+      matchlen=$(expr "$1" : "${head_pattern#+}")
+      test "$matchlen" = ${#1} || continue
+
+      # if non-ff, $heads must be with the '+' prefix
+      test -n "$noff" &&
+      test "$head_pattern" = "$heads" && continue
+
+      info "Found matching head pattern: '$head_pattern'"
+      for user_pattern in $user_patterns; do
+        info "Checking user: '$username' against pattern: '$user_pattern'"
+        matchlen=$(expr "$username" : "$user_pattern")
+        if test "$matchlen" = "${#username}"
+        then
+          grant "Allowing user: '$username' with pattern: '$user_pattern'"
+        fi
+      done
+      deny "The user is not in the access list for this branch"
+    done
+  )
+  case "$rc" in
+    grant) grant >/dev/null "Granting access based on $allowed_users_file" ;;
+    deny)  deny  >/dev/null "Denying  access based on $allowed_users_file" ;;
+    *) ;;
+  esac
+fi
+
+allowed_groups_file=$GIT_DIR/info/allowed-groups
+groups=$(id -G -n)
+info "The user belongs to the following groups:"
+info "'$groups'"
+
+if test -f "$allowed_groups_file"
+then
+  rc=$(cat $allowed_groups_file | grep -v '^#' | grep -v '^$' |
+    while read heads group_patterns
+    do
+      # does this rule apply to us?
+      head_pattern=${heads#+}
+      matchlen=$(expr "$1" : "${head_pattern#+}")
+      test "$matchlen" = ${#1} || continue
+
+      # if non-ff, $heads must be with the '+' prefix
+      test -n "$noff" &&
+      test "$head_pattern" = "$heads" && continue
+
+      info "Found matching head pattern: '$head_pattern'"
+      for group_pattern in $group_patterns; do
+        for groupname in $groups; do
+          info "Checking group: '$groupname' against pattern: '$group_pattern'"
+          matchlen=$(expr "$groupname" : "$group_pattern")
+          if test "$matchlen" = "${#groupname}"
+          then
+            grant "Allowing group: '$groupname' with pattern: '$group_pattern'"
+          fi
+        done
+      done
+      deny "None of the user's groups are in the access list for this branch"
+    done
+  )
+  case "$rc" in
+    grant) grant >/dev/null "Granting access based on $allowed_groups_file" ;;
+    deny)  deny  >/dev/null "Denying  access based on $allowed_groups_file" ;;
+    *) ;;
+  esac
+fi
+
+deny >/dev/null "There are no more rules to check.  Denying access"
+----------------------------------------------------
+
+This uses two files, $GIT_DIR/info/allowed-users and
+allowed-groups, to describe which heads can be pushed into by
+whom.  The format of each file would look like this:
+
+    refs/heads/master   junio
+    +refs/heads/pu      junio
+    refs/heads/cogito$  pasky
+    refs/heads/bw/.*    linus
+    refs/heads/tmp/.*   .*
+    refs/tags/v[0-9].*  junio
+
+With this, Linus can push or create "bw/penguin" or "bw/zebra"
+or "bw/panda" branches, Pasky can do only "cogito", and JC can
+do master and pu branches and make versioned tags.  And anybody
+can do tmp/blah branches. The '+' sign at the pu record means
+that JC can make non-fast-forward pushes on it.
diff --git a/Documentation/howto/use-git-daemon.txt b/Documentation/howto/use-git-daemon.txt
new file mode 100644
index 000000000000..7af2e52cf312
--- /dev/null
+++ b/Documentation/howto/use-git-daemon.txt
@@ -0,0 +1,54 @@
+Content-type: text/asciidoc
+
+How to use git-daemon
+=====================
+
+Git can be run in inetd mode and in stand alone mode. But all you want is
+let a coworker pull from you, and therefore need to set up a Git server
+real quick, right?
+
+Note that git-daemon is not really chatty at the moment, especially when
+things do not go according to plan (e.g. a socket could not be bound).
+
+Another word of warning: if you run
+
+	$ git ls-remote git://127.0.0.1/rule-the-world.git
+
+and you see a message like
+
+	fatal: The remote end hung up unexpectedly
+
+it only means that _something_ went wrong. To find out _what_ went wrong,
+you have to ask the server. (Git refuses to be more precise for your
+security only. Take off your shoes now. You have any coins in your pockets?
+Sorry, not allowed -- who knows what you planned to do with them?)
+
+With these two caveats, let's see an example:
+
+	$ git daemon --reuseaddr --verbose --base-path=/home/gitte/git \
+	  --export-all -- /home/gitte/git/rule-the-world.git
+
+(Of course, unless your user name is `gitte` _and_ your repository is in
+~/rule-the-world.git, you have to adjust the paths. If your repository is
+not bare, be aware that you have to type the path to the .git directory!)
+
+This invocation tries to reuse the address if it is already taken
+(this can save you some debugging, because otherwise killing and restarting
+git-daemon could just silently fail to bind to a socket).
+
+Also, it is (relatively) verbose when somebody actually connects to it.
+It also sets the base path, which means that all the projects which can be
+accessed using this daemon have to reside in or under that path.
+
+The option `--export-all` just means that you _don't_ have to create a
+file named `git-daemon-export-ok` in each exported repository. (Otherwise,
+git-daemon would complain loudly, and refuse to cooperate.)
+
+Last of all, the repository which should be exported is specified. It is
+a good practice to put the paths after a "--" separator.
+
+Now, test your daemon with
+
+	$ git ls-remote git://127.0.0.1/rule-the-world.git
+
+If this does not work, find out why, and submit a patch to this document.
diff --git a/Documentation/howto/using-merge-subtree.txt b/Documentation/howto/using-merge-subtree.txt
new file mode 100644
index 000000000000..a499a94ac228
--- /dev/null
+++ b/Documentation/howto/using-merge-subtree.txt
@@ -0,0 +1,75 @@
+Date: Sat, 5 Jan 2008 20:17:40 -0500
+From: Sean <seanlkml@sympatico.ca>
+To: Miklos Vajna <vmiklos@frugalware.org>
+Cc: git@vger.kernel.org
+Subject: how to use git merge -s subtree?
+Abstract: In this article, Sean demonstrates how one can use the subtree merge
+ strategy.
+Content-type: text/asciidoc
+Message-ID: <BAYC1-PASMTP12374B54BA370A1E1C6E78AE4E0@CEZ.ICE>
+
+How to use the subtree merge strategy
+=====================================
+
+There are situations where you want to include contents in your project
+from an independently developed project. You can just pull from the
+other project as long as there are no conflicting paths.
+
+The problematic case is when there are conflicting files. Potential
+candidates are Makefiles and other standard filenames. You could merge
+these files but probably you do not want to.  A better solution for this
+problem can be to merge the project as its own subdirectory. This is not
+supported by the 'recursive' merge strategy, so just pulling won't work.
+
+What you want is the 'subtree' merge strategy, which helps you in such a
+situation.
+
+In this example, let's say you have the repository at `/path/to/B` (but
+it can be a URL as well, if you want). You want to merge the 'master'
+branch of that repository to the `dir-B` subdirectory in your current
+branch.
+
+Here is the command sequence you need:
+
+----------------
+$ git remote add -f Bproject /path/to/B <1>
+$ git merge -s ours --no-commit --allow-unrelated-histories Bproject/master <2>
+$ git read-tree --prefix=dir-B/ -u Bproject/master <3>
+$ git commit -m "Merge B project as our subdirectory" <4>
+
+$ git pull -s subtree Bproject master <5>
+----------------
+<1> name the other project "Bproject", and fetch.
+<2> prepare for the later step to record the result as a merge.
+<3> read "master" branch of Bproject to the subdirectory "dir-B".
+<4> record the merge result.
+<5> maintain the result with subsequent merges using "subtree"
+
+The first four commands are used for the initial merge, while the last
+one is to merge updates from 'B project'.
+
+Comparing 'subtree' merge with submodules
+-----------------------------------------
+
+- The benefit of using subtree merge is that it requires less
+  administrative burden from the users of your repository. It works with
+  older (before Git v1.5.2) clients and you have the code right after
+  clone.
+
+- However if you use submodules then you can choose not to transfer the
+  submodule objects. This may be a problem with the subtree merge.
+
+- Also, in case you make changes to the other project, it is easier to
+  submit changes if you just use submodules.
+
+Additional tips
+---------------
+
+- If you made changes to the other project in your repository, they may
+  want to merge from your project. This is possible using subtree -- it
+  can shift up the paths in your tree and then they can merge only the
+  relevant parts of your tree.
+
+- Please note that if the other project merges from you, then it will
+  connect its history to yours, which can be something they don't want
+  to.
diff --git a/Documentation/howto/using-signed-tag-in-pull-request.txt b/Documentation/howto/using-signed-tag-in-pull-request.txt
new file mode 100644
index 000000000000..bbf040eda8af
--- /dev/null
+++ b/Documentation/howto/using-signed-tag-in-pull-request.txt
@@ -0,0 +1,217 @@
+From: Junio C Hamano <gitster@pobox.com>
+Date: Tue, 17 Jan 2011 13:00:00 -0800
+Subject: Using signed tag in pull requests
+Abstract: Beginning v1.7.9, a contributor can push a signed tag to her
+ publishing repository and ask her integrator to pull it. This assures the
+ integrator that the pulled history is authentic and allows others to
+ later validate it.
+Content-type: text/asciidoc
+
+How to use a signed tag in pull requests
+========================================
+
+A typical distributed workflow using Git is for a contributor to fork a
+project, build on it, publish the result to her public repository, and ask
+the "upstream" person (often the owner of the project where she forked
+from) to pull from her public repository. Requesting such a "pull" is made
+easy by the `git request-pull` command.
+
+Earlier, a typical pull request may have started like this:
+
+------------
+ The following changes since commit 406da78032179...:
+
+   Froboz 3.2 (2011-09-30 14:20:57 -0700)
+
+ are available in the Git repository at:
+
+   example.com:/git/froboz.git for-xyzzy
+------------
+
+followed by a shortlog of the changes and a diffstat.
+
+The request was for a branch name (e.g. `for-xyzzy`) in the public
+repository of the contributor, and even though it stated where the
+contributor forked her work from, the message did not say anything about
+the commit to expect at the tip of the for-xyzzy branch. If the site that
+hosts the public repository of the contributor cannot be fully trusted, it
+was unnecessarily hard to make sure what was pulled by the integrator was
+genuinely what the contributor had produced for the project. Also there
+was no easy way for third-party auditors to later verify the resulting
+history.
+
+Starting from Git release v1.7.9, a contributor can add a signed tag to
+the commit at the tip of the history and ask the integrator to pull that
+signed tag. When the integrator runs `git pull`, the signed tag is
+automatically verified to assure that the history is not tampered with.
+In addition, the resulting merge commit records the content of the signed
+tag, so that other people can verify that the branch merged by the
+integrator was signed by the contributor, without fetching the signed tag
+used to validate the pull request separately and keeping it in the refs
+namespace.
+
+This document describes the workflow between the contributor and the
+integrator, using Git v1.7.9 or later.
+
+
+A contributor or a lieutenant
+-----------------------------
+
+After preparing her work to be pulled, the contributor uses `git tag -s`
+to create a signed tag:
+
+------------
+ $ git checkout work
+ $ ... "git pull" from sublieutenants, "git commit" your own work ...
+ $ git tag -s -m "Completed frotz feature" frotz-for-xyzzy work
+------------
+
+Note that this example uses the `-m` option to create a signed tag with
+just a one-liner message, but this is for illustration purposes only. It
+is advisable to compose a well-written explanation of what the topic does
+to justify why it is worthwhile for the integrator to pull it, as this
+message will eventually become part of the final history after the
+integrator responds to the pull request (as we will see later).
+
+Then she pushes the tag out to her public repository:
+
+------------
+ $ git push example.com:/git/froboz.git/ +frotz-for-xyzzy
+------------
+
+There is no need to push the `work` branch or anything else.
+
+Note that the above command line used a plus sign at the beginning of
+`+frotz-for-xyzzy` to allow forcing the update of a tag, as the same
+contributor may want to reuse a signed tag with the same name after the
+previous pull request has already been responded to.
+
+The contributor then prepares a message to request a "pull":
+
+------------
+ $ git request-pull v3.2 example.com:/git/froboz.git/ frotz-for-xyzzy >msg.txt
+------------
+
+The arguments are:
+
+. the version of the integrator's commit the contributor based her work on;
+. the URL of the repository, to which the contributor has pushed what she
+  wants to get pulled; and
+. the name of the tag the contributor wants to get pulled (earlier, she could
+  write only a branch name here).
+
+The resulting msg.txt file begins like so:
+
+------------
+ The following changes since commit 406da78032179...:
+
+   Froboz 3.2 (2011-09-30 14:20:57 -0700)
+
+ are available in the Git repository at:
+
+   example.com:/git/froboz.git tags/frotz-for-xyzzy
+
+ for you to fetch changes up to 703f05ad5835c...:
+
+   Add tests and documentation for frotz (2011-12-02 10:02:52 -0800)
+
+ -----------------------------------------------
+ Completed frotz feature
+ -----------------------------------------------
+------------
+
+followed by a shortlog of the changes and a diffstat.  Comparing this with
+the earlier illustration of the output from the traditional `git request-pull`
+command, the reader should notice that:
+
+. The tip commit to expect is shown to the integrator; and
+. The signed tag message is shown prominently between the dashed lines
+  before the shortlog.
+
+The latter is why the contributor would want to justify why pulling her
+work is worthwhile when creating the signed tag.  The contributor then
+opens her favorite MUA, reads msg.txt, edits and sends it to her upstream
+integrator.
+
+
+Integrator
+----------
+
+After receiving such a pull request message, the integrator fetches and
+integrates the tag named in the request, with:
+
+------------
+ $ git pull example.com:/git/froboz.git/ tags/frotz-for-xyzzy
+------------
+
+This operation will always open an editor to allow the integrator to fine
+tune the commit log message when merging a signed tag.  Also, pulling a
+signed tag will always create a merge commit even when the integrator does
+not have any new commit since the contributor's work forked (i.e. 'fast
+forward'), so that the integrator can properly explain what the merge is
+about and why it was made.
+
+In the editor, the integrator will see something like this:
+
+------------
+ Merge tag 'frotz-for-xyzzy' of example.com:/git/froboz.git/
+
+ Completed frotz feature
+ # gpg: Signature made Fri 02 Dec 2011 10:03:01 AM PST using RSA key ID 96AFE6CB
+ # gpg: Good signature from "Con Tributor <nitfol@example.com>"
+------------
+
+Notice that the message recorded in the signed tag "Completed frotz
+feature" appears here, and again that is why it is important for the
+contributor to explain her work well when creating the signed tag.
+
+As usual, the lines commented with `#` are stripped out. The resulting
+commit records the signed tag used for this validation in a hidden field
+so that it can later be used by others to audit the history. There is no
+need for the integrator to keep a separate copy of the tag in his
+repository (i.e. `git tag -l` won't list the `frotz-for-xyzzy` tag in the
+above example), and there is no need to publish the tag to his public
+repository, either.
+
+After the integrator responds to the pull request and her work becomes
+part of the permanent history, the contributor can remove the tag from
+her public repository, if she chooses, in order to keep the tag namespace
+of her public repository clean, with:
+
+------------
+ $ git push example.com:/git/froboz.git :frotz-for-xyzzy
+------------
+
+
+Auditors
+--------
+
+The `--show-signature` option can be given to `git log` or `git show` and
+shows the verification status of the embedded signed tag in merge commits
+created when the integrator responded to a pull request of a signed tag.
+
+A typical output from `git show --show-signature` may look like this:
+
+------------
+ $ git show --show-signature
+ commit 02306ef6a3498a39118aef9df7975bdb50091585
+ merged tag 'frotz-for-xyzzy'
+ gpg: Signature made Fri 06 Jan 2012 12:41:49 PM PST using RSA key ID 96AFE6CB
+ gpg: Good signature from "Con Tributor <nitfol@example.com>"
+ Merge: 406da78 703f05a
+ Author: Inte Grator <xyzzy@example.com>
+ Date:   Tue Jan 17 13:49:41 2012 -0800
+
+     Merge tag 'frotz-for-xyzzy' of example.com:/git/froboz.git/
+
+     Completed frotz feature
+
+     * tag 'frotz-for-xyzzy' (100 commits)
+       Add tests and documentation for frotz
+       ...
+------------
+
+There is no need for the auditor to explicitly fetch the contributor's
+signature, or to even be aware of what tag(s) the contributor and integrator
+used to communicate the signature.  All the required information is recorded
+as part of the merge commit.