1 files changed, 277 insertions, 157 deletions

diff --git a/lockfile.c b/lockfile.c
index 8fbcb6a98a..993bb82748 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -2,60 +2,61 @@
  * Copyright (c) 2005, Junio C Hamano
  */
 #include "cache.h"
+#include "lockfile.h"
 #include "sigchain.h"
 
-static struct lock_file *lock_file_list;
-static const char *alternate_index_output;
+static struct lock_file *volatile lock_file_list;
 
-static void remove_lock_file(void)
+static void remove_lock_files(int skip_fclose)
 {
 	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) {
+			/* fclose() is not safe to call in a signal handler */
+			if (skip_fclose)
+				lock_file_list->fp = NULL;
+			rollback_lock_file(lock_file_list);
 		}
 		lock_file_list = lock_file_list->next;
 	}
 }
 
-static void remove_lock_file_on_signal(int signo)
+static void remove_lock_files_on_exit(void)
 {
-	remove_lock_file();
+	remove_lock_files(0);
+}
+
+static void remove_lock_files_on_signal(int signo)
+{
+	remove_lock_files(1);
 	sigchain_pop(signo);
 	raise(signo);
 }
 
 /*
- * 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);
 }
 
 
@@ -63,134 +64,188 @@ static char *last_path_elm(char *p)
 #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 (!lock_file_list) {
+		/* One-time initialization */
+		sigchain_push_common(remove_lock_files_on_signal);
+		atexit(remove_lock_files_on_exit);
+	}
+
+	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->fp = NULL;
+		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);
+	}
 
-	if (strlen(path) >= max_path_len)
+	if (flags & LOCK_NO_DEREF) {
+		strbuf_add_absolute_path(&lk->filename, path);
+	} else {
+		struct strbuf resolved_path = STRBUF_INIT;
+
+		strbuf_add(&resolved_path, path, pathlen);
+		resolve_symlink(&resolved_path);
+		strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
+		strbuf_release(&resolved_path);
+	}
+
+	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;
-	strcpy(lk->filename, path);
-	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))
-			return error("cannot fix permission bits on %s",
-				     lk->filename);
 	}
-	else
-		lk->filename[0] = 0;
 	return lk->fd;
 }
 
-static char *unable_to_lock_message(const char *path, int err)
+/*
+ * 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)
 {
-	struct strbuf buf = STRBUF_INIT;
+	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"
+		strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
 		    "If no other git process is currently running, this probably means a\n"
 		    "git process crashed in this repository earlier. Make sure no other git\n"
 		    "process is running and remove the file manually to continue.",
 			    absolute_path(path), strerror(err));
 	} else
-		strbuf_addf(&buf, "Unable to create '%s.lock': %s",
+		strbuf_addf(buf, "Unable to create '%s.lock': %s",
 			    absolute_path(path), strerror(err));
-	return strbuf_detach(&buf, NULL);
 }
 
-int unable_to_lock_error(const char *path, int err)
+NORETURN void unable_to_lock_die(const char *path, int err)
 {
-	char *msg = unable_to_lock_message(path, err);
-	error("%s", msg);
-	free(msg);
-	return -1;
-}
+	struct strbuf buf = STRBUF_INIT;
 
-NORETURN void unable_to_lock_index_die(const char *path, int err)
-{
-	die("%s", unable_to_lock_message(path, err));
+	unable_to_lock_message(path, err, &buf);
+	die("%s", buf.buf);
 }
 
-int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
+/* 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(lk, path, flags);
+	int fd = lock_file_timeout(lk, path, flags, timeout_ms);
 	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
-		unable_to_lock_index_die(path, errno);
+		unable_to_lock_die(path, errno);
 	return fd;
 }
 
@@ -201,82 +256,147 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
 	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;
 	}
 
 	orig_fd = open(path, O_RDONLY);
 	if (orig_fd < 0) {
 		if (errno != ENOENT) {
+			int save_errno = errno;
+
 			if (flags & LOCK_DIE_ON_ERROR)
 				die("cannot open '%s' for copying", path);
-			close(fd);
-			return error("cannot open '%s' for copying", path);
+			rollback_lock_file(lk);
+			error("cannot open '%s' for copying", path);
+			errno = save_errno;
+			return -1;
 		}
 	} else if (copy_fd(orig_fd, fd)) {
+		int save_errno = errno;
+
 		if (flags & LOCK_DIE_ON_ERROR)
-			exit(128);
-		close(fd);
+			die("failed to prepare '%s' for appending", path);
+		close(orig_fd);
+		rollback_lock_file(lk);
+		errno = save_errno;
 		return -1;
+	} else {
+		close(orig_fd);
 	}
 	return fd;
 }
 
+FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
+{
+	if (!lk->active)
+		die("BUG: fdopen_lock_file() called for unlocked object");
+	if (lk->fp)
+		die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);
+
+	lk->fp = fdopen(lk->fd, mode);
+	return lk->fp;
+}
+
+char *get_locked_file_path(struct lock_file *lk)
+{
+	if (!lk->active)
+		die("BUG: get_locked_file_path() called for unlocked object");
+	if (lk->filename.len <= LOCK_SUFFIX_LEN)
+		die("BUG: get_locked_file_path() called for malformed lock object");
+	return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
+}
+
 int close_lock_file(struct lock_file *lk)
 {
 	int fd = lk->fd;
+	FILE *fp = lk->fp;
+	int err;
+
+	if (fd < 0)
+		return 0;
+
 	lk->fd = -1;
-	return close(fd);
-}
+	if (fp) {
+		lk->fp = NULL;
+
+		/*
+		 * Note: no short-circuiting here; we want to fclose()
+		 * in any case!
+		 */
+		err = ferror(fp) | fclose(fp);
+	} else {
+		err = close(fd);
+	}
 
-int commit_lock_file(struct lock_file *lk)
-{
-	char result_file[PATH_MAX];
-	size_t i;
-	if (lk->fd >= 0 && 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 (err) {
+		int save_errno = errno;
+		rollback_lock_file(lk);
+		errno = save_errno;
 		return -1;
-	lk->filename[0] = 0;
+	}
+
 	return 0;
 }
 
-int hold_locked_index(struct lock_file *lk, int die_on_error)
+int reopen_lock_file(struct lock_file *lk)
 {
-	return hold_lock_file_for_update(lk, get_index_file(),
-					 die_on_error
-					 ? LOCK_DIE_ON_ERROR
-					 : 0);
+	if (0 <= lk->fd)
+		die(_("BUG: reopen a lockfile that is still open"));
+	if (!lk->active)
+		die(_("BUG: reopen a lockfile that has been committed"));
+	lk->fd = open(lk->filename.buf, O_WRONLY);
+	return lk->fd;
 }
 
-void set_alternate_index_output(const char *name)
+int commit_lock_file_to(struct lock_file *lk, const char *path)
 {
-	alternate_index_output = name;
+	if (!lk->active)
+		die("BUG: attempt to commit unlocked object to \"%s\"", path);
+
+	if (close_lock_file(lk))
+		return -1;
+
+	if (rename(lk->filename.buf, path)) {
+		int save_errno = errno;
+		rollback_lock_file(lk);
+		errno = save_errno;
+		return -1;
+	}
+
+	lk->active = 0;
+	strbuf_reset(&lk->filename);
+	return 0;
 }
 
-int commit_locked_index(struct lock_file *lk)
+int commit_lock_file(struct lock_file *lk)
 {
-	if (alternate_index_output) {
-		if (lk->fd >= 0 && close_lock_file(lk))
-			return -1;
-		if (rename(lk->filename, alternate_index_output))
-			return -1;
-		lk->filename[0] = 0;
-		return 0;
-	}
-	else
-		return commit_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;
 }
 
 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;
 }