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git/lockfile.c
Junio C Hamano 3f061bf514 lockfile: LOCK_REPORT_ON_ERROR
The "libify sequencer" topic stopped passing the die_on_error option
to hold_locked_index(), and this lost an error message from "git
merge --ff-only $commit" when there are competing updates in
progress.

The command still exits with a non-zero status, but that is not of
much help for an interactive user.  The last thing the command says
is "Updating $from..$to".  We used to follow it with a big error
message that makes it clear that "merge --ff-only" did not succeed.

What is sad is that we should have noticed this regression while
reviewing the change.  It was clear that the update to the
checkout_fast_forward() function made a failing hold_locked_index()
silent, but the only caller of the checkout_fast_forward() function
had this comment:

	    if (checkout_fast_forward(from, to, 1))
    -               exit(128); /* the callee should have complained already */
    +               return -1; /* the callee should have complained already */

which clearly contradicted the assumption X-<.

Add a new option LOCK_REPORT_ON_ERROR that can be passed instead of
LOCK_DIE_ON_ERROR to the hold_lock*() family of functions and teach
checkout_fast_forward() to use it to fix this regression.

After going thourgh all calls to hold_lock*() family of functions
that used to pass LOCK_DIE_ON_ERROR but were modified to pass 0 in
the "libify sequencer" topic "git show --first-parent 2a4062a4a8",
it appears that this is the only one that has become silent.  Many
others used to give detailed report that talked about "there may be
competing Git process running" but with the series merged they now
only give a single liner "Unable to lock ...", some of which may
have to be tweaked further, but at least they say something, unlike
the one this patch fixes.

Reported-by: Robbie Iannucci <iannucci@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-12-07 11:31:59 -08:00

215 lines
5.6 KiB
C

/*
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
#include "lockfile.h"
/*
* path = absolute or relative path name
*
* Remove the last path name element from path (leaving the preceding
* "/", if any). If path is empty or the root directory ("/"), set
* path to the empty string.
*/
static void trim_last_path_component(struct strbuf *path)
{
int i = path->len;
/* back up past trailing slashes, if any */
while (i && path->buf[i - 1] == '/')
i--;
/*
* then go backwards until a slash, or the beginning of the
* string
*/
while (i && path->buf[i - 1] != '/')
i--;
strbuf_setlen(path, i);
}
/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5
/*
* path contains a path that might be a symlink.
*
* If path is a symlink, attempt to overwrite it with a path to the
* real file or directory (which may or may not exist), following a
* chain of symlinks if necessary. Otherwise, leave path unmodified.
*
* This is a best-effort routine. If an error occurs, path will
* either be left unmodified or will name a different symlink in a
* symlink chain that started with the original path.
*/
static void resolve_symlink(struct strbuf *path)
{
int depth = MAXDEPTH;
static struct strbuf link = STRBUF_INIT;
while (depth--) {
if (strbuf_readlink(&link, path->buf, path->len) < 0)
break;
if (is_absolute_path(link.buf))
/* absolute path simply replaces p */
strbuf_reset(path);
else
/*
* link is a relative path, so replace the
* last element of p with it.
*/
trim_last_path_component(path);
strbuf_addbuf(path, &link);
}
strbuf_reset(&link);
}
/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
int fd;
struct strbuf filename = STRBUF_INIT;
strbuf_addstr(&filename, path);
if (!(flags & LOCK_NO_DEREF))
resolve_symlink(&filename);
strbuf_addstr(&filename, LOCK_SUFFIX);
fd = create_tempfile(&lk->tempfile, filename.buf);
strbuf_release(&filename);
return fd;
}
/*
* Constants defining the gaps between attempts to lock a file. The
* first backoff period is approximately INITIAL_BACKOFF_MS
* milliseconds. The longest backoff period is approximately
* (BACKOFF_MAX_MULTIPLIER * INITIAL_BACKOFF_MS) milliseconds.
*/
#define INITIAL_BACKOFF_MS 1L
#define BACKOFF_MAX_MULTIPLIER 1000
/*
* Try locking path, retrying with quadratic backoff for at least
* timeout_ms milliseconds. If timeout_ms is 0, try locking the file
* exactly once. If timeout_ms is -1, try indefinitely.
*/
static int lock_file_timeout(struct lock_file *lk, const char *path,
int flags, long timeout_ms)
{
int n = 1;
int multiplier = 1;
long remaining_ms = 0;
static int random_initialized = 0;
if (timeout_ms == 0)
return lock_file(lk, path, flags);
if (!random_initialized) {
srand((unsigned int)getpid());
random_initialized = 1;
}
if (timeout_ms > 0)
remaining_ms = timeout_ms;
while (1) {
long backoff_ms, wait_ms;
int fd;
fd = lock_file(lk, path, flags);
if (fd >= 0)
return fd; /* success */
else if (errno != EEXIST)
return -1; /* failure other than lock held */
else if (timeout_ms > 0 && remaining_ms <= 0)
return -1; /* failure due to timeout */
backoff_ms = multiplier * INITIAL_BACKOFF_MS;
/* back off for between 0.75*backoff_ms and 1.25*backoff_ms */
wait_ms = (750 + rand() % 500) * backoff_ms / 1000;
sleep_millisec(wait_ms);
remaining_ms -= wait_ms;
/* Recursion: (n+1)^2 = n^2 + 2n + 1 */
multiplier += 2*n + 1;
if (multiplier > BACKOFF_MAX_MULTIPLIER)
multiplier = BACKOFF_MAX_MULTIPLIER;
else
n++;
}
}
void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
{
if (err == EEXIST) {
strbuf_addf(buf, _("Unable to create '%s.lock': %s.\n\n"
"Another git process seems to be running in this repository, e.g.\n"
"an editor opened by 'git commit'. Please make sure all processes\n"
"are terminated then try again. If it still fails, a git process\n"
"may have crashed in this repository earlier:\n"
"remove the file manually to continue."),
absolute_path(path), strerror(err));
} else
strbuf_addf(buf, _("Unable to create '%s.lock': %s"),
absolute_path(path), strerror(err));
}
NORETURN void unable_to_lock_die(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;
unable_to_lock_message(path, err, &buf);
die("%s", buf.buf);
}
/* This should return a meaningful errno on failure */
int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
int flags, long timeout_ms)
{
int fd = lock_file_timeout(lk, path, flags, timeout_ms);
if (fd < 0) {
if (flags & LOCK_DIE_ON_ERROR)
unable_to_lock_die(path, errno);
if (flags & LOCK_REPORT_ON_ERROR) {
struct strbuf buf = STRBUF_INIT;
unable_to_lock_message(path, errno, &buf);
error("%s", buf.buf);
strbuf_release(&buf);
}
}
return fd;
}
char *get_locked_file_path(struct lock_file *lk)
{
struct strbuf ret = STRBUF_INIT;
strbuf_addstr(&ret, get_tempfile_path(&lk->tempfile));
if (ret.len <= LOCK_SUFFIX_LEN ||
strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
die("BUG: get_locked_file_path() called for malformed lock object");
/* remove ".lock": */
strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN);
return strbuf_detach(&ret, NULL);
}
int commit_lock_file(struct lock_file *lk)
{
char *result_path = get_locked_file_path(lk);
if (commit_lock_file_to(lk, result_path)) {
int save_errno = errno;
free(result_path);
errno = save_errno;
return -1;
}
free(result_path);
return 0;
}