#include "cache.h"
#include "sigchain.h"
-static struct lock_file *lock_file_list;
+/*
+ * File write-locks as used by Git.
+ *
+ * For an overview of how to use the lockfile API, please see
+ *
+ * Documentation/technical/api-lockfile.txt
+ *
+ * This module keeps track of all locked files in lock_file_list for
+ * use at cleanup. This list and the lock_file objects that comprise
+ * it must be kept in self-consistent states at all time, because the
+ * program can be interrupted any time by a signal, in which case the
+ * signal handler will walk through the list attempting to clean up
+ * any open lock files.
+ *
+ * A lockfile is owned by the process that created it. The lock_file
+ * object has an "owner" field that records its owner. This field is
+ * used to prevent a forked process from closing a lockfile created by
+ * its parent.
+ *
+ * The possible states of a lock_file object are as follows:
+ *
+ * - Uninitialized. In this state the object's on_list field must be
+ * zero but the rest of its contents need not be initialized. As
+ * soon as the object is used in any way, it is irrevocably
+ * registered in the lock_file_list, and on_list is set.
+ *
+ * - Locked, lockfile open (after hold_lock_file_for_update(),
+ * hold_lock_file_for_append(), or reopen_lock_file()). In this
+ * state:
+ * - the lockfile exists
+ * - active is set
+ * - filename holds the filename of the lockfile
+ * - fd holds a file descriptor open for writing to the lockfile
+ * - owner holds the PID of the process that locked the file
+ *
+ * - Locked, lockfile closed (after successful close_lock_file()).
+ * Same as the previous state, except that the lockfile is closed
+ * and fd is -1.
+ *
+ * - Unlocked (after commit_lock_file(), commit_lock_file_to(),
+ * rollback_lock_file(), a failed attempt to lock, or a failed
+ * close_lock_file()). In this state:
+ * - active is unset
+ * - filename is empty (usually, though there are transitory
+ * states in which this condition doesn't hold). Client code should
+ * *not* rely on the filename being empty in this state.
+ * - fd is -1
+ * - the object is left registered in the lock_file_list, and
+ * on_list is set.
+ */
+
+static struct lock_file *volatile lock_file_list;
static void remove_lock_file(void)
{
pid_t me = getpid();
while (lock_file_list) {
- if (lock_file_list->owner == me &&
- lock_file_list->filename[0]) {
- if (lock_file_list->fd >= 0)
- close(lock_file_list->fd);
- unlink_or_warn(lock_file_list->filename);
- }
+ if (lock_file_list->owner == me)
+ rollback_lock_file(lock_file_list);
lock_file_list = lock_file_list->next;
}
}
}
/*
- * p = absolute or relative path name
+ * path = absolute or relative path name
*
- * Return a pointer into p showing the beginning of the last path name
- * element. If p is empty or the root directory ("/"), just return p.
+ * 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 char *last_path_elm(char *p)
+static void trim_last_path_component(struct strbuf *path)
{
- /* r starts pointing to null at the end of the string */
- char *r = strchr(p, '\0');
-
- if (r == p)
- return p; /* just return empty string */
-
- r--; /* back up to last non-null character */
+ int i = path->len;
/* back up past trailing slashes, if any */
- while (r > p && *r == '/')
- r--;
+ while (i && path->buf[i - 1] == '/')
+ i--;
/*
- * then go backwards until I hit a slash, or the beginning of
- * the string
+ * then go backwards until a slash, or the beginning of the
+ * string
*/
- while (r > p && *(r-1) != '/')
- r--;
- return r;
+ while (i && path->buf[i - 1] != '/')
+ i--;
+
+ strbuf_setlen(path, i);
}
#define MAXDEPTH 5
/*
- * p = path that may be a symlink
- * s = full size of p
- *
- * If p is a symlink, attempt to overwrite p with a path to the real
- * file or directory (which may or may not exist), following a chain of
- * symlinks if necessary. Otherwise, leave p unmodified.
+ * path contains a path that might be a symlink.
*
- * This is a best-effort routine. If an error occurs, p will either be
- * left unmodified or will name a different symlink in a symlink chain
- * that started with p's initial contents.
+ * 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.
*
- * Always returns p.
+ * 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 char *resolve_symlink(char *p, size_t s)
+static void resolve_symlink(struct strbuf *path)
{
int depth = MAXDEPTH;
+ static struct strbuf link = STRBUF_INIT;
while (depth--) {
- char link[PATH_MAX];
- int link_len = readlink(p, link, sizeof(link));
- if (link_len < 0) {
- /* not a symlink anymore */
- return p;
- }
- else if (link_len < sizeof(link))
- /* readlink() never null-terminates */
- link[link_len] = '\0';
- else {
- warning("%s: symlink too long", p);
- return p;
- }
+ if (strbuf_readlink(&link, path->buf, path->len) < 0)
+ break;
- if (is_absolute_path(link)) {
+ if (is_absolute_path(link.buf))
/* absolute path simply replaces p */
- if (link_len < s)
- strcpy(p, link);
- else {
- warning("%s: symlink too long", p);
- return p;
- }
- } else {
+ strbuf_reset(path);
+ else
/*
- * link is a relative path, so I must replace the
+ * link is a relative path, so replace the
* last element of p with it.
*/
- char *r = (char *)last_path_elm(p);
- if (r - p + link_len < s)
- strcpy(r, link);
- else {
- warning("%s: symlink too long", p);
- return p;
- }
- }
+ trim_last_path_component(path);
+
+ strbuf_addbuf(path, &link);
}
- return p;
+ 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)
{
- /*
- * subtract 5 from size to make sure there's room for adding
- * ".lock" for the lock file name
- */
- static const size_t max_path_len = sizeof(lk->filename) - 5;
+ size_t pathlen = strlen(path);
- if (strlen(path) >= max_path_len) {
- errno = ENAMETOOLONG;
- return -1;
+ if (!lock_file_list) {
+ /* One-time initialization */
+ sigchain_push_common(remove_lock_file_on_signal);
+ atexit(remove_lock_file);
+ }
+
+ if (lk->active)
+ die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
+ path);
+ if (!lk->on_list) {
+ /* Initialize *lk and add it to lock_file_list: */
+ lk->fd = -1;
+ lk->active = 0;
+ lk->owner = 0;
+ strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
+ lk->next = lock_file_list;
+ lock_file_list = lk;
+ lk->on_list = 1;
+ } else if (lk->filename.len) {
+ /* This shouldn't happen, but better safe than sorry. */
+ die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
+ path);
}
- strcpy(lk->filename, path);
+
+ strbuf_add(&lk->filename, path, pathlen);
if (!(flags & LOCK_NODEREF))
- resolve_symlink(lk->filename, max_path_len);
- strcat(lk->filename, ".lock");
- lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
- if (0 <= lk->fd) {
- if (!lock_file_list) {
- sigchain_push_common(remove_lock_file_on_signal);
- atexit(remove_lock_file);
- }
- lk->owner = getpid();
- if (!lk->on_list) {
- lk->next = lock_file_list;
- lock_file_list = lk;
- lk->on_list = 1;
- }
- if (adjust_shared_perm(lk->filename)) {
- int save_errno = errno;
- error("cannot fix permission bits on %s",
- lk->filename);
- errno = save_errno;
- return -1;
- }
+ resolve_symlink(&lk->filename);
+ strbuf_addstr(&lk->filename, LOCK_SUFFIX);
+ lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
+ if (lk->fd < 0) {
+ strbuf_reset(&lk->filename);
+ return -1;
+ }
+ lk->owner = getpid();
+ lk->active = 1;
+ if (adjust_shared_perm(lk->filename.buf)) {
+ int save_errno = errno;
+ error("cannot fix permission bits on %s", lk->filename.buf);
+ rollback_lock_file(lk);
+ errno = save_errno;
+ return -1;
}
- else
- lk->filename[0] = 0;
return lk->fd;
}
return -1;
}
-NORETURN void unable_to_lock_index_die(const char *path, int err)
+NORETURN void unable_to_lock_die(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;
{
int fd = lock_file(lk, path, flags);
if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
- unable_to_lock_index_die(path, errno);
+ unable_to_lock_die(path, errno);
return fd;
}
fd = lock_file(lk, path, flags);
if (fd < 0) {
if (flags & LOCK_DIE_ON_ERROR)
- unable_to_lock_index_die(path, errno);
+ unable_to_lock_die(path, errno);
return fd;
}
if (errno != ENOENT) {
if (flags & LOCK_DIE_ON_ERROR)
die("cannot open '%s' for copying", path);
- close(fd);
+ rollback_lock_file(lk);
return error("cannot open '%s' for copying", path);
}
} else if (copy_fd(orig_fd, fd)) {
if (flags & LOCK_DIE_ON_ERROR)
exit(128);
- close(fd);
+ rollback_lock_file(lk);
return -1;
}
return fd;
int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;
+
+ if (fd < 0)
+ return 0;
+
lk->fd = -1;
- return close(fd);
+ if (close(fd)) {
+ int save_errno = errno;
+ rollback_lock_file(lk);
+ errno = save_errno;
+ return -1;
+ }
+ return 0;
}
int reopen_lock_file(struct lock_file *lk)
{
if (0 <= lk->fd)
die(_("BUG: reopen a lockfile that is still open"));
- if (!lk->filename[0])
+ if (!lk->active)
die(_("BUG: reopen a lockfile that has been committed"));
- lk->fd = open(lk->filename, O_WRONLY);
+ lk->fd = open(lk->filename.buf, O_WRONLY);
return lk->fd;
}
-int commit_lock_file(struct lock_file *lk)
+int commit_lock_file_to(struct lock_file *lk, const char *path)
{
- char result_file[PATH_MAX];
- size_t i;
- if (lk->fd >= 0 && close_lock_file(lk))
+ if (!lk->active)
+ die("BUG: attempt to commit unlocked object to \"%s\"", path);
+
+ if (close_lock_file(lk))
return -1;
- strcpy(result_file, lk->filename);
- i = strlen(result_file) - 5; /* .lock */
- result_file[i] = 0;
- if (rename(lk->filename, result_file))
+
+ if (rename(lk->filename.buf, path)) {
+ int save_errno = errno;
+ rollback_lock_file(lk);
+ errno = save_errno;
return -1;
- lk->filename[0] = 0;
+ }
+
+ lk->active = 0;
+ strbuf_reset(&lk->filename);
return 0;
}
+int commit_lock_file(struct lock_file *lk)
+{
+ static struct strbuf result_file = STRBUF_INIT;
+ int err;
+
+ if (!lk->active)
+ die("BUG: attempt to commit unlocked object");
+
+ if (lk->filename.len <= LOCK_SUFFIX_LEN ||
+ strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
+ die("BUG: lockfile filename corrupt");
+
+ /* remove ".lock": */
+ strbuf_add(&result_file, lk->filename.buf,
+ lk->filename.len - LOCK_SUFFIX_LEN);
+ err = commit_lock_file_to(lk, result_file.buf);
+ strbuf_reset(&result_file);
+ return err;
+}
+
int hold_locked_index(struct lock_file *lk, int die_on_error)
{
return hold_lock_file_for_update(lk, get_index_file(),
void rollback_lock_file(struct lock_file *lk)
{
- if (lk->filename[0]) {
- if (lk->fd >= 0)
- close(lk->fd);
- unlink_or_warn(lk->filename);
+ if (!lk->active)
+ return;
+
+ if (!close_lock_file(lk)) {
+ unlink_or_warn(lk->filename.buf);
+ lk->active = 0;
+ strbuf_reset(&lk->filename);
}
- lk->filename[0] = 0;
}
projects / thirdparty / git.git / blobdiff