1 files changed, 136 insertions, 213 deletions

diff --git a/lockfile.c b/lockfile.c
index 8fbcb6a98a..80d056d2ed 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -1,61 +1,33 @@
 /*
  * Copyright (c) 2005, Junio C Hamano
  */
-#include "cache.h"
-#include "sigchain.h"
-
-static struct lock_file *lock_file_list;
-static const char *alternate_index_output;
-
-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);
-		}
-		lock_file_list = lock_file_list->next;
-	}
-}
 
-static void remove_lock_file_on_signal(int signo)
-{
-	remove_lock_file();
-	sigchain_pop(signo);
-	raise(signo);
-}
+#include "cache.h"
+#include "lockfile.h"
 
 /*
- * 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);
 }
 
 
@@ -63,220 +35,171 @@ static char *last_path_elm(char *p)
 #define MAXDEPTH 5
 
 /*
- * p = path that may be a symlink
- * s = full size of p
+ * path contains a path that might be a symlink.
  *
- * 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.
+ * 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, p will either be
- * left unmodified or will name a different symlink in a symlink chain
- * that started with p's initial contents.
- *
- * 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 (is_absolute_path(link)) {
+		if (strbuf_readlink(&link, path->buf, path->len) < 0)
+			break;
+
+		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;
+	int fd;
+	struct strbuf filename = STRBUF_INIT;
 
-	if (strlen(path) >= max_path_len)
-		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;
+	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;
 }
 
-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;
 }
 
-int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
+char *get_locked_file_path(struct lock_file *lk)
 {
-	int fd, orig_fd;
-
-	fd = lock_file(lk, path, flags);
-	if (fd < 0) {
-		if (flags & LOCK_DIE_ON_ERROR)
-			unable_to_lock_index_die(path, errno);
-		return fd;
-	}
-
-	orig_fd = open(path, O_RDONLY);
-	if (orig_fd < 0) {
-		if (errno != ENOENT) {
-			if (flags & LOCK_DIE_ON_ERROR)
-				die("cannot open '%s' for copying", path);
-			close(fd);
-			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);
-		return -1;
-	}
-	return fd;
-}
+	struct strbuf ret = STRBUF_INIT;
 
-int close_lock_file(struct lock_file *lk)
-{
-	int fd = lk->fd;
-	lk->fd = -1;
-	return close(fd);
+	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_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))
-		return -1;
-	lk->filename[0] = 0;
-	return 0;
-}
-
-int hold_locked_index(struct lock_file *lk, int die_on_error)
-{
-	return hold_lock_file_for_update(lk, get_index_file(),
-					 die_on_error
-					 ? LOCK_DIE_ON_ERROR
-					 : 0);
-}
-
-void set_alternate_index_output(const char *name)
-{
-	alternate_index_output = name;
-}
-
-int commit_locked_index(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);
-}
+	char *result_path = get_locked_file_path(lk);
 
-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 (commit_lock_file_to(lk, result_path)) {
+		int save_errno = errno;
+		free(result_path);
+		errno = save_errno;
+		return -1;
 	}
-	lk->filename[0] = 0;
+	free(result_path);
+	return 0;
 }