lockfile: change lock_file::filename into a strbuf

For now, we still make sure to allocate at least PATH_MAX characters
for the strbuf because resolve_symlink() doesn't know how to expand
the space for its return value.  (That will be fixed in a moment.)

Another alternative would be to just use a strbuf as scratch space in
lock_file() but then store a pointer to the naked string in struct
lock_file.  But lock_file objects are often reused.  By reusing the
same strbuf, we can avoid having to reallocate the string most times
when a lock_file object is reused.

Helped-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

8 files changed, 47 insertions, 52 deletions

diff --git a/builtin/commit.c b/builtin/commit.c
index 70f5935f1b..f55e80986b 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -341,7 +341,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			die(_("unable to create temporary index"));
 
 		old_index_env = getenv(INDEX_ENVIRONMENT);
-		setenv(INDEX_ENVIRONMENT, index_lock.filename, 1);
+		setenv(INDEX_ENVIRONMENT, index_lock.filename.buf, 1);
 
 		if (interactive_add(argc, argv, prefix, patch_interactive) != 0)
 			die(_("interactive add failed"));
@@ -352,7 +352,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			unsetenv(INDEX_ENVIRONMENT);
 
 		discard_cache();
-		read_cache_from(index_lock.filename);
+		read_cache_from(index_lock.filename.buf);
 		if (update_main_cache_tree(WRITE_TREE_SILENT) == 0) {
 			if (reopen_lock_file(&index_lock) < 0)
 				die(_("unable to write index file"));
@@ -362,7 +362,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			warning(_("Failed to update main cache tree"));
 
 		commit_style = COMMIT_NORMAL;
-		return index_lock.filename;
+		return index_lock.filename.buf;
 	}
 
 	/*
@@ -385,7 +385,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
 			die(_("unable to write new_index file"));
 		commit_style = COMMIT_NORMAL;
-		return index_lock.filename;
+		return index_lock.filename.buf;
 	}
 
 	/*
@@ -472,9 +472,9 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		die(_("unable to write temporary index file"));
 
 	discard_cache();
-	read_cache_from(false_lock.filename);
+	read_cache_from(false_lock.filename.buf);
 
-	return false_lock.filename;
+	return false_lock.filename.buf;
 }
 
 static int run_status(FILE *fp, const char *index_file, const char *prefix, int nowarn,
diff --git a/builtin/reflog.c b/builtin/reflog.c
index e8a8fb13b9..7c78b15c14 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -431,7 +431,7 @@ static int expire_reflog(const char *ref, const unsigned char *sha1, int unused,
 			 write_str_in_full(lock->lock_fd, "\n") != 1 ||
 			 close_ref(lock) < 0)) {
 			status |= error("Couldn't write %s",
-				lock->lk->filename);
+					lock->lk->filename.buf);
 			unlink(newlog_path);
 		} else if (rename(newlog_path, log_file)) {
 			status |= error("cannot rename %s to %s",
diff --git a/cache.h b/cache.h
index c2ea6f15e6..f81d95fc3c 100644
--- a/cache.h
+++ b/cache.h
@@ -580,7 +580,7 @@ struct lock_file {
 	volatile int fd;
 	volatile pid_t owner;
 	char on_list;
-	char filename[PATH_MAX];
+	struct strbuf filename;
 };
 #define LOCK_DIE_ON_ERROR 1
 #define LOCK_NODEREF 2
diff --git a/config.c b/config.c
index 123ed29963..21107797d3 100644
--- a/config.c
+++ b/config.c
@@ -2024,9 +2024,9 @@ int git_config_set_multivar_in_file(const char *config_filename,
 			MAP_PRIVATE, in_fd, 0);
 		close(in_fd);
 
-		if (chmod(lock->filename, st.st_mode & 07777) < 0) {
+		if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
 			error("chmod on %s failed: %s",
-				lock->filename, strerror(errno));
+				lock->filename.buf, strerror(errno));
 			ret = CONFIG_NO_WRITE;
 			goto out_free;
 		}
@@ -2106,7 +2106,7 @@ out_free:
 	return ret;
 
 write_err_out:
-	ret = write_error(lock->filename);
+	ret = write_error(lock->filename.buf);
 	goto out_free;
 
 }
@@ -2207,9 +2207,9 @@ int git_config_rename_section_in_file(const char *config_filename,
 
 	fstat(fileno(config_file), &st);
 
-	if (chmod(lock->filename, st.st_mode & 07777) < 0) {
+	if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
 		ret = error("chmod on %s failed: %s",
-				lock->filename, strerror(errno));
+				lock->filename.buf, strerror(errno));
 		goto out;
 	}
 
@@ -2230,7 +2230,7 @@ int git_config_rename_section_in_file(const char *config_filename,
 				}
 				store.baselen = strlen(new_name);
 				if (!store_write_section(out_fd, new_name)) {
-					ret = write_error(lock->filename);
+					ret = write_error(lock->filename.buf);
 					goto out;
 				}
 				/*
@@ -2256,7 +2256,7 @@ int git_config_rename_section_in_file(const char *config_filename,
 			continue;
 		length = strlen(output);
 		if (write_in_full(out_fd, output, length) != length) {
-			ret = write_error(lock->filename);
+			ret = write_error(lock->filename.buf);
 			goto out;
 		}
 	}
diff --git a/lockfile.c b/lockfile.c
index 1dd118f556..85c8648c51 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -47,9 +47,9 @@
  *   failed attempt to lock, or a failed close_lock_file()).  In this
  *   state:
  *   - active is unset
- *   - filename[0] == '\0' (usually, though there are transitory states
- *     in which this condition doesn't hold). Client code should *not*
- *     rely on this fact!
+ *   - 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.
@@ -170,13 +170,6 @@ static char *resolve_symlink(char *p, size_t s)
 /* Make sure errno contains a meaningful value on error */
 static int lock_file(struct lock_file *lk, const char *path, int flags)
 {
-	/*
-	 * subtract LOCK_SUFFIX_LEN 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) -
-					   LOCK_SUFFIX_LEN;
-
 	if (!lock_file_list) {
 		/* One-time initialization */
 		sigchain_push_common(remove_lock_file_on_signal);
@@ -191,30 +184,32 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 		lk->fd = -1;
 		lk->active = 0;
 		lk->owner = 0;
-		lk->filename[0] = 0;
+		strbuf_init(&lk->filename, PATH_MAX);
 		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) {
-		errno = ENAMETOOLONG;
-		return -1;
+	strbuf_addstr(&lk->filename, path);
+	if (!(flags & LOCK_NODEREF)) {
+		resolve_symlink(lk->filename.buf, lk->filename.alloc);
+		strbuf_setlen(&lk->filename, strlen(lk->filename.buf));
 	}
-	strcpy(lk->filename, path);
-	if (!(flags & LOCK_NODEREF))
-		resolve_symlink(lk->filename, max_path_len);
-	strcat(lk->filename, LOCK_SUFFIX);
-	lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
+	strbuf_addstr(&lk->filename, LOCK_SUFFIX);
+	lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
 	if (lk->fd < 0) {
-		lk->filename[0] = 0;
+		strbuf_reset(&lk->filename);
 		return -1;
 	}
 	lk->owner = getpid();
 	lk->active = 1;
-	if (adjust_shared_perm(lk->filename)) {
+	if (adjust_shared_perm(lk->filename.buf)) {
 		int save_errno = errno;
-		error("cannot fix permission bits on %s", lk->filename);
+		error("cannot fix permission bits on %s", lk->filename.buf);
 		rollback_lock_file(lk);
 		errno = save_errno;
 		return -1;
@@ -313,7 +308,7 @@ int reopen_lock_file(struct lock_file *lk)
 		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, O_WRONLY);
+	lk->fd = open(lk->filename.buf, O_WRONLY);
 	return lk->fd;
 }
 
@@ -329,9 +324,9 @@ int commit_lock_file(struct lock_file *lk)
 		return -1;
 
 	/* remove ".lock": */
-	strbuf_add(&result_file, lk->filename,
-		   strlen(lk->filename) - LOCK_SUFFIX_LEN);
-	err = rename(lk->filename, result_file.buf);
+	strbuf_add(&result_file, lk->filename.buf,
+		   lk->filename.len - LOCK_SUFFIX_LEN);
+	err = rename(lk->filename.buf, result_file.buf);
 	strbuf_reset(&result_file);
 	if (err) {
 		int save_errno = errno;
@@ -341,7 +336,7 @@ int commit_lock_file(struct lock_file *lk)
 	}
 
 	lk->active = 0;
-	lk->filename[0] = 0;
+	strbuf_reset(&lk->filename);
 	return 0;
 }
 
@@ -359,8 +354,8 @@ void rollback_lock_file(struct lock_file *lk)
 		return;
 
 	if (!close_lock_file(lk)) {
-		unlink_or_warn(lk->filename);
+		unlink_or_warn(lk->filename.buf);
 		lk->active = 0;
-		lk->filename[0] = 0;
+		strbuf_reset(&lk->filename);
 	}
 }
diff --git a/read-cache.c b/read-cache.c
index af69f344a2..91bf876ee6 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2044,10 +2044,10 @@ static int commit_locked_index(struct lock_file *lk)
 	if (alternate_index_output) {
 		if (close_lock_file(lk))
 			return -1;
-		if (rename(lk->filename, alternate_index_output))
+		if (rename(lk->filename.buf, alternate_index_output))
 			return -1;
 		lk->active = 0;
-		lk->filename[0] = 0;
+		strbuf_reset(&lk->filename);
 		return 0;
 	} else {
 		return commit_lock_file(lk);
diff --git a/refs.c b/refs.c
index a4151315e3..598f4eb9e7 100644
--- a/refs.c
+++ b/refs.c
@@ -2607,8 +2607,8 @@ static int delete_ref_loose(struct ref_lock *lock, int flag)
 		 * lockfile name, minus ".lock":
 		 */
 		char *loose_filename = xmemdupz(
-				lock->lk->filename,
-				strlen(lock->lk->filename) - LOCK_SUFFIX_LEN);
+				lock->lk->filename.buf,
+				lock->lk->filename.len - LOCK_SUFFIX_LEN);
 		int err = unlink_or_warn(loose_filename);
 		free(loose_filename);
 		if (err && errno != ENOENT)
@@ -2972,7 +2972,7 @@ int write_ref_sha1(struct ref_lock *lock,
 	    write_in_full(lock->lock_fd, &term, 1) != 1 ||
 	    close_ref(lock) < 0) {
 		int save_errno = errno;
-		error("Couldn't write %s", lock->lk->filename);
+		error("Couldn't write %s", lock->lk->filename.buf);
 		unlock_ref(lock);
 		errno = save_errno;
 		return -1;
diff --git a/shallow.c b/shallow.c
index 57f4afa6b4..4919baf772 100644
--- a/shallow.c
+++ b/shallow.c
@@ -269,8 +269,8 @@ void setup_alternate_shallow(struct lock_file *shallow_lock,
 	if (write_shallow_commits(&sb, 0, extra)) {
 		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 			die_errno("failed to write to %s",
-				  shallow_lock->filename);
-		*alternate_shallow_file = shallow_lock->filename;
+				  shallow_lock->filename.buf);
+		*alternate_shallow_file = shallow_lock->filename.buf;
 	} else
 		/*
 		 * is_repository_shallow() sees empty string as "no
@@ -316,7 +316,7 @@ void prune_shallow(int show_only)
 	if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
 		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 			die_errno("failed to write to %s",
-				  shallow_lock.filename);
+				  shallow_lock.filename.buf);
 		commit_lock_file(&shallow_lock);
 	} else {
 		unlink(git_path("shallow"));