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-trace API
-=========
-
-The trace API can be used to print debug messages to stderr or a file. Trace
-code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment
-variables.
-
-The trace implementation automatically adds `timestamp file:line ... \n` to
-all trace messages. E.g.:
-
-------------
-23:59:59.123456 git.c:312               trace: built-in: git 'foo'
-00:00:00.000001 builtin/foo.c:99        foo: some message
-------------
-
-Data Structures
----------------
-
-`struct trace_key`::
-
-	Defines a trace key (or category). The default (for API functions that
-	don't take a key) is `GIT_TRACE`.
-+
-E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`:
-+
-------------
-static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);
-
-static void trace_print_foo(const char *message)
-{
-	trace_printf_key(&trace_foo, "%s", message);
-}
-------------
-+
-Note: don't use `const` as the trace implementation stores internal state in
-the `trace_key` structure.
-
-Functions
----------
-
-`int trace_want(struct trace_key *key)`::
-
-	Checks whether the trace key is enabled. Used to prevent expensive
-	string formatting before calling one of the printing APIs.
-
-`void trace_disable(struct trace_key *key)`::
-
-	Disables tracing for the specified key, even if the environment
-	variable was set.
-
-`void trace_printf(const char *format, ...)`::
-`void trace_printf_key(struct trace_key *key, const char *format, ...)`::
-
-	Prints a formatted message, similar to printf.
-
-`void trace_argv_printf(const char **argv, const char *format, ...)``::
-
-	Prints a formatted message, followed by a quoted list of arguments.
-
-`void trace_strbuf(struct trace_key *key, const struct strbuf *data)`::
-
-	Prints the strbuf, without additional formatting (i.e. doesn't
-	choke on `%` or even `\0`).
-
-`uint64_t getnanotime(void)`::
-
-	Returns nanoseconds since the epoch (01/01/1970), typically used
-	for performance measurements.
-+
-Currently there are high precision timer implementations for Linux (using
-`clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`).
-Other platforms use `gettimeofday` as time source.
-
-`void trace_performance(uint64_t nanos, const char *format, ...)`::
-`void trace_performance_since(uint64_t start, const char *format, ...)`::
-
-	Prints the elapsed time (in nanoseconds), or elapsed time since
-	`start`, followed by a formatted message. Enabled via environment
-	variable `GIT_TRACE_PERFORMANCE`. Used for manual profiling, e.g.:
-+
-------------
-uint64_t start = getnanotime();
-/* code section to measure */
-trace_performance_since(start, "foobar");
-------------
-+
-------------
-uint64_t t = 0;
-for (;;) {
-	/* ignore */
-	t -= getnanotime();
-	/* code section to measure */
-	t += getnanotime();
-	/* ignore */
-}
-trace_performance(t, "frotz");
-------------
-
-Bugs & Caveats
---------------
-
-GIT_TRACE_* environment variables can be used to tell Git to show
-trace output to its standard error stream. Git can often spawn a pager
-internally to run its subcommand and send its standard output and
-standard error to it.
-
-Because GIT_TRACE_PERFORMANCE trace is generated only at the very end
-of the program with atexit(), which happens after the pager exits, it
-would not work well if you send its log to the standard error output
-and let Git spawn the pager at the same time.
-
-As a work around, you can for example use '--no-pager', or set
-GIT_TRACE_PERFORMANCE to another file descriptor which is redirected
-to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its
-absolute path.
-
-For example instead of the following command which by default may not
-print any performance information:
-
-------------
-GIT_TRACE_PERFORMANCE=2 git log -1
-------------
-
-you may want to use:
-
-------------
-GIT_TRACE_PERFORMANCE=2 git --no-pager log -1
-------------
-
-or:
-
-------------
-GIT_TRACE_PERFORMANCE=3 3>&2 git log -1
-------------
-
-or:
-
-------------
-GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1
-------------