trace.c - jrn/git - Git at Google

 /*
  * GIT - The information manager from hell
  *
  * Copyright (C) 2000-2002 Michael R. Elkins <me@mutt.org>
  * Copyright (C) 2002-2004 Oswald Buddenhagen <ossi@users.sf.net>
  * Copyright (C) 2004 Theodore Y. Ts'o <tytso@mit.edu>
  * Copyright (C) 2006 Mike McCormack
  * Copyright (C) 2006 Christian Couder
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
  */

 #include "cache.h"
 #include "quote.h"

 struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
 struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);

 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
 {
 	const char *trace;

 	/* don't open twice */
 	if (key->initialized)
 		return key->fd;

 	trace = getenv(key->key);

 	if (!trace || !strcmp(trace, "") ||
 	    !strcmp(trace, "0") || !strcasecmp(trace, "false"))
 		key->fd = 0;
 	else if (!strcmp(trace, "1") || !strcasecmp(trace, "true"))
 		key->fd = STDERR_FILENO;
 	else if (strlen(trace) == 1 && isdigit(*trace))
 		key->fd = atoi(trace);
 	else if (is_absolute_path(trace)) {
 		int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
 		if (fd == -1) {
 			warning("could not open '%s' for tracing: %s",
 				trace, strerror(errno));
 			trace_disable(key);
 		} else {
 			key->fd = fd;
 			key->need_close = 1;
 		}
 	} else {
 		warning("unknown trace value for '%s': %s\n"
 			"         If you want to trace into a file, then please set %s\n"
 			"         to an absolute pathname (starting with /)",
 			key->key, trace, key->key);
 		trace_disable(key);
 	}

 	key->initialized = 1;
 	return key->fd;
 }

 void trace_disable(struct trace_key *key)
 {
 	if (key->need_close)
 		close(key->fd);
 	key->fd = 0;
 	key->initialized = 1;
 	key->need_close = 0;
 }

 static int prepare_trace_line(const char *file, int line,
 			      struct trace_key *key, struct strbuf *buf)
 {
 	static struct trace_key trace_bare = TRACE_KEY_INIT(BARE);
 	struct timeval tv;
 	struct tm tm;
 	time_t secs;

 	if (!trace_want(key))
 		return 0;

 	set_try_to_free_routine(NULL);	/* is never reset */

 	/* unit tests may want to disable additional trace output */
 	if (trace_want(&trace_bare))
 		return 1;

 	/* print current timestamp */
 	gettimeofday(&tv, NULL);
 	secs = tv.tv_sec;
 	localtime_r(&secs, &tm);
 	strbuf_addf(buf, "%02d:%02d:%02d.%06ld ", tm.tm_hour, tm.tm_min,
 		    tm.tm_sec, (long) tv.tv_usec);

 #ifdef HAVE_VARIADIC_MACROS
 	/* print file:line */
 	strbuf_addf(buf, "%s:%d ", file, line);
 	/* align trace output (column 40 catches most files names in git) */
 	while (buf->len < 40)
 		strbuf_addch(buf, ' ');
 #endif

 	return 1;
 }

 static void trace_write(struct trace_key *key, const void *buf, unsigned len)
 {
 	if (write_in_full(get_trace_fd(key), buf, len) < 0) {
 		warning("unable to write trace for %s: %s",
 			key->key, strerror(errno));
 		trace_disable(key);
 	}
 }

 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len)
 {
 	if (!trace_want(key))
 		return;
 	trace_write(key, buf, len);
 }

 static void print_trace_line(struct trace_key *key, struct strbuf *buf)
 {
 	strbuf_complete_line(buf);
 	trace_write(key, buf->buf, buf->len);
 	strbuf_release(buf);
 }

 static void trace_vprintf_fl(const char *file, int line, struct trace_key *key,
 			     const char *format, va_list ap)
 {
 	struct strbuf buf = STRBUF_INIT;

 	if (!prepare_trace_line(file, line, key, &buf))
 		return;

 	strbuf_vaddf(&buf, format, ap);
 	print_trace_line(key, &buf);
 }

 static void trace_argv_vprintf_fl(const char *file, int line,
 				  const char **argv, const char *format,
 				  va_list ap)
 {
 	struct strbuf buf = STRBUF_INIT;

 	if (!prepare_trace_line(file, line, &trace_default_key, &buf))
 		return;

 	strbuf_vaddf(&buf, format, ap);

 	sq_quote_argv(&buf, argv, 0);
 	print_trace_line(&trace_default_key, &buf);
 }

 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 		     const struct strbuf *data)
 {
 	struct strbuf buf = STRBUF_INIT;

 	if (!prepare_trace_line(file, line, key, &buf))
 		return;

 	strbuf_addbuf(&buf, data);
 	print_trace_line(key, &buf);
 }

 static void trace_performance_vprintf_fl(const char *file, int line,
 					 uint64_t nanos, const char *format,
 					 va_list ap)
 {
 	struct strbuf buf = STRBUF_INIT;

 	if (!prepare_trace_line(file, line, &trace_perf_key, &buf))
 		return;

 	strbuf_addf(&buf, "performance: %.9f s", (double) nanos / 1000000000);

 	if (format && *format) {
 		strbuf_addstr(&buf, ": ");
 		strbuf_vaddf(&buf, format, ap);
 	}

 	print_trace_line(&trace_perf_key, &buf);
 }

 #ifndef HAVE_VARIADIC_MACROS

 void trace_printf(const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_vprintf_fl(NULL, 0, &trace_default_key, format, ap);
 	va_end(ap);
 }

 void trace_printf_key(struct trace_key *key, const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_vprintf_fl(NULL, 0, key, format, ap);
 	va_end(ap);
 }

 void trace_argv_printf(const char **argv, const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_argv_vprintf_fl(NULL, 0, argv, format, ap);
 	va_end(ap);
 }

 void trace_strbuf(struct trace_key *key, const struct strbuf *data)
 {
 	trace_strbuf_fl(NULL, 0, key, data);
 }

 void trace_performance(uint64_t nanos, const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_performance_vprintf_fl(NULL, 0, nanos, format, ap);
 	va_end(ap);
 }

 void trace_performance_since(uint64_t start, const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_performance_vprintf_fl(NULL, 0, getnanotime() - start,
 				     format, ap);
 	va_end(ap);
 }

 #else

 void trace_printf_key_fl(const char *file, int line, struct trace_key *key,
 			 const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_vprintf_fl(file, line, key, format, ap);
 	va_end(ap);
 }

 void trace_argv_printf_fl(const char *file, int line, const char **argv,
 			  const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_argv_vprintf_fl(file, line, argv, format, ap);
 	va_end(ap);
 }

 void trace_performance_fl(const char *file, int line, uint64_t nanos,
 			      const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
 	trace_performance_vprintf_fl(file, line, nanos, format, ap);
 	va_end(ap);
 }

 #endif /* HAVE_VARIADIC_MACROS */


 static const char *quote_crnl(const char *path)
 {
 	static struct strbuf new_path = STRBUF_INIT;

 	if (!path)
 		return NULL;

 	strbuf_reset(&new_path);

 	while (*path) {
 		switch (*path) {
 		case '\\': strbuf_addstr(&new_path, "\\\\"); break;
 		case '\n': strbuf_addstr(&new_path, "\\n"); break;
 		case '\r': strbuf_addstr(&new_path, "\\r"); break;
 		default:
 			strbuf_addch(&new_path, *path);
 		}
 		path++;
 	}
 	return new_path.buf;
 }

 /* FIXME: move prefix to startup_info struct and get rid of this arg */
 void trace_repo_setup(const char *prefix)
 {
 	static struct trace_key key = TRACE_KEY_INIT(SETUP);
 	const char *git_work_tree;
 	char *cwd;

 	if (!trace_want(&key))
 		return;

 	cwd = xgetcwd();

 	if (!(git_work_tree = get_git_work_tree()))
 		git_work_tree = "(null)";

 	if (!prefix)
 		prefix = "(null)";

 	trace_printf_key(&key, "setup: git_dir: %s\n", quote_crnl(get_git_dir()));
 	trace_printf_key(&key, "setup: git_common_dir: %s\n", quote_crnl(get_git_common_dir()));
 	trace_printf_key(&key, "setup: worktree: %s\n", quote_crnl(git_work_tree));
 	trace_printf_key(&key, "setup: cwd: %s\n", quote_crnl(cwd));
 	trace_printf_key(&key, "setup: prefix: %s\n", quote_crnl(prefix));

 	free(cwd);
 }

 int trace_want(struct trace_key *key)
 {
 	return !!get_trace_fd(key);
 }

 #if defined(HAVE_CLOCK_GETTIME) && defined(HAVE_CLOCK_MONOTONIC)

 static inline uint64_t highres_nanos(void)
 {
 	struct timespec ts;
 	if (clock_gettime(CLOCK_MONOTONIC, &ts))
 		return 0;
 	return (uint64_t) ts.tv_sec * 1000000000 + ts.tv_nsec;
 }

 #elif defined (GIT_WINDOWS_NATIVE)

 static inline uint64_t highres_nanos(void)
 {
 	static uint64_t high_ns, scaled_low_ns;
 	static int scale;
 	LARGE_INTEGER cnt;

 	if (!scale) {
 		if (!QueryPerformanceFrequency(&cnt))
 			return 0;

 		/* high_ns = number of ns per cnt.HighPart */
 		high_ns = (1000000000LL << 32) / (uint64_t) cnt.QuadPart;

 		/*
 		 * Number of ns per cnt.LowPart is 10^9 / frequency (or
 		 * high_ns >> 32). For maximum precision, we scale this factor
 		 * so that it just fits within 32 bit (i.e. won't overflow if
 		 * multiplied with cnt.LowPart).
 		 */
 		scaled_low_ns = high_ns;
 		scale = 32;
 		while (scaled_low_ns >= 0x100000000LL) {
 			scaled_low_ns >>= 1;
 			scale--;
 		}
 	}

 	/* if QPF worked on initialization, we expect QPC to work as well */
 	QueryPerformanceCounter(&cnt);

 	return (high_ns * cnt.HighPart) +
 	       ((scaled_low_ns * cnt.LowPart) >> scale);
 }

 #else
 # define highres_nanos() 0
 #endif

 static inline uint64_t gettimeofday_nanos(void)
 {
 	struct timeval tv;
 	gettimeofday(&tv, NULL);
 	return (uint64_t) tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
 }

 /*
  * Returns nanoseconds since the epoch (01/01/1970), for performance tracing
  * (i.e. favoring high precision over wall clock time accuracy).
  */
 uint64_t getnanotime(void)
 {
 	static uint64_t offset;
 	if (offset > 1) {
 		/* initialization succeeded, return offset + high res time */
 		return offset + highres_nanos();
 	} else if (offset == 1) {
 		/* initialization failed, fall back to gettimeofday */
 		return gettimeofday_nanos();
 	} else {
 		/* initialize offset if high resolution timer works */
 		uint64_t now = gettimeofday_nanos();
 		uint64_t highres = highres_nanos();
 		if (highres)
 			offset = now - highres;
 		else
 			offset = 1;
 		return now;
 	}
 }

 static uint64_t command_start_time;
 static struct strbuf command_line = STRBUF_INIT;

 static void print_command_performance_atexit(void)
 {
 	trace_performance_since(command_start_time, "git command:%s",
 				command_line.buf);
 }

 void trace_command_performance(const char **argv)
 {
 	if (!trace_want(&trace_perf_key))
 		return;

 	if (!command_start_time)
 		atexit(print_command_performance_atexit);

 	strbuf_reset(&command_line);
 	sq_quote_argv(&command_line, argv, 0);
 	command_start_time = getnanotime();
 }
	/*
	* GIT - The information manager from hell
	*
	* Copyright (C) 2000-2002 Michael R. Elkins <me@mutt.org>
	* Copyright (C) 2002-2004 Oswald Buddenhagen <ossi@users.sf.net>
	* Copyright (C) 2004 Theodore Y. Ts'o <tytso@mit.edu>
	* Copyright (C) 2006 Mike McCormack
	* Copyright (C) 2006 Christian Couder
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, see <http://www.gnu.org/licenses/>.
	*/

	#include "cache.h"
	#include "quote.h"

	struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
	struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);

	/* Get a trace file descriptor from "key" env variable. */
	static int get_trace_fd(struct trace_key *key)
	{
	const char *trace;

	/* don't open twice */
	if (key->initialized)
	return key->fd;

	trace = getenv(key->key);

	if (!trace \|\| !strcmp(trace, "") \|\|
	!strcmp(trace, "0") \|\| !strcasecmp(trace, "false"))
	key->fd = 0;
	else if (!strcmp(trace, "1") \|\| !strcasecmp(trace, "true"))
	key->fd = STDERR_FILENO;
	else if (strlen(trace) == 1 && isdigit(*trace))
	key->fd = atoi(trace);
	else if (is_absolute_path(trace)) {
	int fd = open(trace, O_WRONLY \| O_APPEND \| O_CREAT, 0666);
	if (fd == -1) {
	warning("could not open '%s' for tracing: %s",
	trace, strerror(errno));
	trace_disable(key);
	} else {
	key->fd = fd;
	key->need_close = 1;
	}
	} else {
	warning("unknown trace value for '%s': %s\n"
	" If you want to trace into a file, then please set %s\n"
	" to an absolute pathname (starting with /)",
	key->key, trace, key->key);
	trace_disable(key);
	}

	key->initialized = 1;
	return key->fd;
	}

	void trace_disable(struct trace_key *key)
	{
	if (key->need_close)
	close(key->fd);
	key->fd = 0;
	key->initialized = 1;
	key->need_close = 0;
	}

	static int prepare_trace_line(const char *file, int line,
	struct trace_key key, struct strbuf buf)
	{
	static struct trace_key trace_bare = TRACE_KEY_INIT(BARE);
	struct timeval tv;
	struct tm tm;
	time_t secs;

	if (!trace_want(key))
	return 0;

	set_try_to_free_routine(NULL); /* is never reset */

	/* unit tests may want to disable additional trace output */
	if (trace_want(&trace_bare))
	return 1;

	/* print current timestamp */
	gettimeofday(&tv, NULL);
	secs = tv.tv_sec;
	localtime_r(&secs, &tm);
	strbuf_addf(buf, "%02d:%02d:%02d.%06ld ", tm.tm_hour, tm.tm_min,
	tm.tm_sec, (long) tv.tv_usec);

	#ifdef HAVE_VARIADIC_MACROS
	/* print file:line */
	strbuf_addf(buf, "%s:%d ", file, line);
	/* align trace output (column 40 catches most files names in git) */
	while (buf->len < 40)
	strbuf_addch(buf, ' ');
	#endif

	return 1;
	}

	static void trace_write(struct trace_key key, const void buf, unsigned len)
	{
	if (write_in_full(get_trace_fd(key), buf, len) < 0) {
	warning("unable to write trace for %s: %s",
	key->key, strerror(errno));
	trace_disable(key);
	}
	}

	void trace_verbatim(struct trace_key key, const void buf, unsigned len)
	{
	if (!trace_want(key))
	return;
	trace_write(key, buf, len);
	}

	static void print_trace_line(struct trace_key key, struct strbuf buf)
	{
	strbuf_complete_line(buf);
	trace_write(key, buf->buf, buf->len);
	strbuf_release(buf);
	}

	static void trace_vprintf_fl(const char file, int line, struct trace_key key,
	const char *format, va_list ap)
	{
	struct strbuf buf = STRBUF_INIT;

	if (!prepare_trace_line(file, line, key, &buf))
	return;

	strbuf_vaddf(&buf, format, ap);
	print_trace_line(key, &buf);
	}

	static void trace_argv_vprintf_fl(const char *file, int line,
	const char *argv, const char format,
	va_list ap)
	{
	struct strbuf buf = STRBUF_INIT;

	if (!prepare_trace_line(file, line, &trace_default_key, &buf))
	return;

	strbuf_vaddf(&buf, format, ap);

	sq_quote_argv(&buf, argv, 0);
	print_trace_line(&trace_default_key, &buf);
	}

	void trace_strbuf_fl(const char file, int line, struct trace_key key,
	const struct strbuf *data)
	{
	struct strbuf buf = STRBUF_INIT;

	if (!prepare_trace_line(file, line, key, &buf))
	return;

	strbuf_addbuf(&buf, data);
	print_trace_line(key, &buf);
	}

	static void trace_performance_vprintf_fl(const char *file, int line,
	uint64_t nanos, const char *format,
	va_list ap)
	{
	struct strbuf buf = STRBUF_INIT;

	if (!prepare_trace_line(file, line, &trace_perf_key, &buf))
	return;

	strbuf_addf(&buf, "performance: %.9f s", (double) nanos / 1000000000);

	if (format && *format) {
	strbuf_addstr(&buf, ": ");
	strbuf_vaddf(&buf, format, ap);
	}

	print_trace_line(&trace_perf_key, &buf);
	}

	#ifndef HAVE_VARIADIC_MACROS

	void trace_printf(const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_vprintf_fl(NULL, 0, &trace_default_key, format, ap);
	va_end(ap);
	}

	void trace_printf_key(struct trace_key key, const char format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_vprintf_fl(NULL, 0, key, format, ap);
	va_end(ap);
	}

	void trace_argv_printf(const char *argv, const char format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_argv_vprintf_fl(NULL, 0, argv, format, ap);
	va_end(ap);
	}

	void trace_strbuf(struct trace_key key, const struct strbuf data)
	{
	trace_strbuf_fl(NULL, 0, key, data);
	}

	void trace_performance(uint64_t nanos, const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_performance_vprintf_fl(NULL, 0, nanos, format, ap);
	va_end(ap);
	}

	void trace_performance_since(uint64_t start, const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_performance_vprintf_fl(NULL, 0, getnanotime() - start,
	format, ap);
	va_end(ap);
	}

	#else

	void trace_printf_key_fl(const char file, int line, struct trace_key key,
	const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_vprintf_fl(file, line, key, format, ap);
	va_end(ap);
	}

	void trace_argv_printf_fl(const char file, int line, const char *argv,
	const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_argv_vprintf_fl(file, line, argv, format, ap);
	va_end(ap);
	}

	void trace_performance_fl(const char *file, int line, uint64_t nanos,
	const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	trace_performance_vprintf_fl(file, line, nanos, format, ap);
	va_end(ap);
	}

	#endif /* HAVE_VARIADIC_MACROS */


	static const char quote_crnl(const char path)
	{
	static struct strbuf new_path = STRBUF_INIT;

	if (!path)
	return NULL;

	strbuf_reset(&new_path);

	while (*path) {
	switch (*path) {
	case '\\': strbuf_addstr(&new_path, "\\\\"); break;
	case '\n': strbuf_addstr(&new_path, "\\n"); break;
	case '\r': strbuf_addstr(&new_path, "\\r"); break;
	default:
	strbuf_addch(&new_path, *path);
	}
	path++;
	}
	return new_path.buf;
	}

	/* FIXME: move prefix to startup_info struct and get rid of this arg */
	void trace_repo_setup(const char *prefix)
	{
	static struct trace_key key = TRACE_KEY_INIT(SETUP);
	const char *git_work_tree;
	char *cwd;

	if (!trace_want(&key))
	return;

	cwd = xgetcwd();

	if (!(git_work_tree = get_git_work_tree()))
	git_work_tree = "(null)";

	if (!prefix)
	prefix = "(null)";

	trace_printf_key(&key, "setup: git_dir: %s\n", quote_crnl(get_git_dir()));
	trace_printf_key(&key, "setup: git_common_dir: %s\n", quote_crnl(get_git_common_dir()));
	trace_printf_key(&key, "setup: worktree: %s\n", quote_crnl(git_work_tree));
	trace_printf_key(&key, "setup: cwd: %s\n", quote_crnl(cwd));
	trace_printf_key(&key, "setup: prefix: %s\n", quote_crnl(prefix));

	free(cwd);
	}

	int trace_want(struct trace_key *key)
	{
	return !!get_trace_fd(key);
	}

	#if defined(HAVE_CLOCK_GETTIME) && defined(HAVE_CLOCK_MONOTONIC)

	static inline uint64_t highres_nanos(void)
	{
	struct timespec ts;
	if (clock_gettime(CLOCK_MONOTONIC, &ts))
	return 0;
	return (uint64_t) ts.tv_sec * 1000000000 + ts.tv_nsec;
	}

	#elif defined (GIT_WINDOWS_NATIVE)

	static inline uint64_t highres_nanos(void)
	{
	static uint64_t high_ns, scaled_low_ns;
	static int scale;
	LARGE_INTEGER cnt;

	if (!scale) {
	if (!QueryPerformanceFrequency(&cnt))
	return 0;

	/* high_ns = number of ns per cnt.HighPart */
	high_ns = (1000000000LL << 32) / (uint64_t) cnt.QuadPart;

	/*
	* Number of ns per cnt.LowPart is 10^9 / frequency (or
	* high_ns >> 32). For maximum precision, we scale this factor
	* so that it just fits within 32 bit (i.e. won't overflow if
	* multiplied with cnt.LowPart).
	*/
	scaled_low_ns = high_ns;
	scale = 32;
	while (scaled_low_ns >= 0x100000000LL) {
	scaled_low_ns >>= 1;
	scale--;
	}
	}

	/* if QPF worked on initialization, we expect QPC to work as well */
	QueryPerformanceCounter(&cnt);

	return (high_ns * cnt.HighPart) +
	((scaled_low_ns * cnt.LowPart) >> scale);
	}

	#else
	# define highres_nanos() 0
	#endif

	static inline uint64_t gettimeofday_nanos(void)
	{
	struct timeval tv;
	gettimeofday(&tv, NULL);
	return (uint64_t) tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
	}

	/*
	* Returns nanoseconds since the epoch (01/01/1970), for performance tracing
	* (i.e. favoring high precision over wall clock time accuracy).
	*/
	uint64_t getnanotime(void)
	{
	static uint64_t offset;
	if (offset > 1) {
	/* initialization succeeded, return offset + high res time */
	return offset + highres_nanos();
	} else if (offset == 1) {
	/* initialization failed, fall back to gettimeofday */
	return gettimeofday_nanos();
	} else {
	/* initialize offset if high resolution timer works */
	uint64_t now = gettimeofday_nanos();
	uint64_t highres = highres_nanos();
	if (highres)
	offset = now - highres;
	else
	offset = 1;
	return now;
	}
	}

	static uint64_t command_start_time;
	static struct strbuf command_line = STRBUF_INIT;

	static void print_command_performance_atexit(void)
	{
	trace_performance_since(command_start_time, "git command:%s",
	command_line.buf);
	}

	void trace_command_performance(const char **argv)
	{
	if (!trace_want(&trace_perf_key))
	return;

	if (!command_start_time)
	atexit(print_command_performance_atexit);

	strbuf_reset(&command_line);
	sq_quote_argv(&command_line, argv, 0);
	command_start_time = getnanotime();
	}