static int write_rr(struct string_list *rr, int out_fd)
{
	int i;
	for (i = 0; i < rr->nr; i++) {
		struct strbuf buf = STRBUF_INIT;
		struct rerere_id *id;

		assert(rr->items[i].util != RERERE_RESOLVED);

		id = rr->items[i].util;
		if (!id)
			continue;
		assert(id->variant >= 0);
		if (0 < id->variant)
			strbuf_addf(&buf, "%s.%d\t%s%c",
				    rerere_id_hex(id), id->variant,
				    rr->items[i].string, 0);
		else
			strbuf_addf(&buf, "%s\t%s%c",
				    rerere_id_hex(id),
				    rr->items[i].string, 0);

		if (write_in_full(out_fd, buf.buf, buf.len) < 0)
			die(_("unable to write rerere record"));

		strbuf_release(&buf);
	}
	if (commit_lock_file(&write_lock) != 0)
		die(_("unable to write rerere record"));
	return 0;
}

int pack_refs(unsigned int flags)
{
	int fd;
	struct pack_refs_cb_data cbdata;

	memset(&cbdata, 0, sizeof(cbdata));
	cbdata.flags = flags;

	fd = hold_lock_file_for_update(&packed, git_path("packed-refs"),
				       LOCK_DIE_ON_ERROR);
	cbdata.refs_file = fdopen(fd, "w");
	if (!cbdata.refs_file)
		die("unable to create ref-pack file structure (%s)",
		    strerror(errno));

	/* perhaps other traits later as well */
	fprintf(cbdata.refs_file, "# pack-refs with: peeled \n");

	for_each_ref(handle_one_ref, &cbdata);
	if (ferror(cbdata.refs_file))
		die("failed to write ref-pack file");
	if (fflush(cbdata.refs_file) || fsync(fd) || fclose(cbdata.refs_file))
		die("failed to write ref-pack file (%s)", strerror(errno));
	/*
	 * Since the lock file was fdopen()'ed and then fclose()'ed above,
	 * assign -1 to the lock file descriptor so that commit_lock_file()
	 * won't try to close() it.
	 */
	packed.fd = -1;
	if (commit_lock_file(&packed) < 0)
		die("unable to overwrite old ref-pack file (%s)", strerror(errno));
	if (cbdata.flags & PACK_REFS_PRUNE)
		prune_refs(cbdata.ref_to_prune);
	return 0;
}

static int repack_without_ref(const char *refname)
{
	struct ref_list *list, *packed_ref_list;
	int fd;
	int found = 0;

	packed_ref_list = get_packed_refs();
	for (list = packed_ref_list; list; list = list->next) {
		if (!strcmp(refname, list->name)) {
			found = 1;
			break;
		}
	}
	if (!found)
		return 0;
	fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
	if (fd < 0)
		return error("cannot delete '%s' from packed refs", refname);

	for (list = packed_ref_list; list; list = list->next) {
		char line[PATH_MAX + 100];
		int len;

		if (!strcmp(refname, list->name))
			continue;
		len = snprintf(line, sizeof(line), "%s %s\n",
			       sha1_to_hex(list->sha1), list->name);
		/* this should not happen but just being defensive */
		if (len > sizeof(line))
			die("too long a refname '%s'", list->name);
		write_or_die(fd, line, len);
	}
	return commit_lock_file(&packlock);
}

int commit_ref(struct ref_lock *lock)
{
	if (commit_lock_file(lock->lk))
		return -1;
	lock->lock_fd = -1;
	return 0;
}

struct ref *fetch_pack(struct fetch_pack_args *my_args,
		       int fd[], struct child_process *conn,
		       const struct ref *ref,
		const char *dest,
		int nr_heads,
		char **heads,
		char **pack_lockfile)
{
	struct stat st;
	struct ref *ref_cpy;

	fetch_pack_setup();
	if (&args != my_args)
		memcpy(&args, my_args, sizeof(args));
	if (args.depth > 0) {
		if (stat(git_path("shallow"), &st))
			st.st_mtime = 0;
	}

	if (heads && nr_heads)
		nr_heads = remove_duplicates(nr_heads, heads);
	if (!ref) {
		packet_flush(fd[1]);
		die("no matching remote head");
	}
	ref_cpy = do_fetch_pack(fd, ref, nr_heads, heads, pack_lockfile);

	if (args.depth > 0) {
		struct cache_time mtime;
		struct strbuf sb = STRBUF_INIT;
		char *shallow = git_path("shallow");
		int fd;

		mtime.sec = st.st_mtime;
		mtime.nsec = ST_MTIME_NSEC(st);
		if (stat(shallow, &st)) {
			if (mtime.sec)
				die("shallow file was removed during fetch");
		} else if (st.st_mtime != mtime.sec
#ifdef USE_NSEC
				|| ST_MTIME_NSEC(st) != mtime.nsec
#endif
			  )
			die("shallow file was changed during fetch");

		fd = hold_lock_file_for_update(&lock, shallow,
					       LOCK_DIE_ON_ERROR);
		if (!write_shallow_commits(&sb, 0)
		 || write_in_full(fd, sb.buf, sb.len) != sb.len) {
			unlink_or_warn(shallow);
			rollback_lock_file(&lock);
		} else {
			commit_lock_file(&lock);
		}
		strbuf_release(&sb);
	}

	reprepare_packed_git();
	return ref_cpy;
}

struct ref *fetch_pack(struct fetch_pack_args *args,
		       int fd[], struct child_process *conn,
		       const struct ref *ref,
		       const char *dest,
		       struct ref **sought, int nr_sought,
		       char **pack_lockfile)
{
	struct ref *ref_cpy;

	fetch_pack_setup();
	if (nr_sought)
		nr_sought = remove_duplicates_in_refs(sought, nr_sought);

	if (!ref) {
		packet_flush(fd[1]);
		die("no matching remote head");
	}
	ref_cpy = do_fetch_pack(args, fd, ref, sought, nr_sought, pack_lockfile);

	if (alternate_shallow_file) {
		if (*alternate_shallow_file == '\0') { /* --unshallow */
			unlink_or_warn(git_path("shallow"));
			rollback_lock_file(&shallow_lock);
		} else
			commit_lock_file(&shallow_lock);
	}

	reprepare_packed_git();
	return ref_cpy;
}

static void process_log_file(void)
{
	struct stat st;
	if (!fstat(get_lock_file_fd(&log_lock), &st) && st.st_size)
		commit_lock_file(&log_lock);
	else
		rollback_lock_file(&log_lock);
}

int write_cache_as_tree(unsigned char *sha1, int flags, const char *prefix)
{
	int entries, was_valid, newfd;
	struct lock_file *lock_file;

	/*
	 * We can't free this memory, it becomes part of a linked list
	 * parsed atexit()
	 */
	lock_file = xcalloc(1, sizeof(struct lock_file));

	newfd = hold_locked_index(lock_file, 1);

	entries = read_cache();
	if (entries < 0)
		return WRITE_TREE_UNREADABLE_INDEX;
	if (flags & WRITE_TREE_IGNORE_CACHE_TREE)
		cache_tree_free(&(active_cache_tree));

	if (!active_cache_tree)
		active_cache_tree = cache_tree();

	was_valid = cache_tree_fully_valid(active_cache_tree);
	if (!was_valid) {
		int missing_ok = flags & WRITE_TREE_MISSING_OK;

		if (cache_tree_update(active_cache_tree,
				      active_cache, active_nr,
				      missing_ok, 0) < 0)
			return WRITE_TREE_UNMERGED_INDEX;
		if (0 <= newfd) {
			if (!write_cache(newfd, active_cache, active_nr) &&
			    !commit_lock_file(lock_file))
				newfd = -1;
		}
		/* Not being able to write is fine -- we are only interested
		 * in updating the cache-tree part, and if the next caller
		 * ends up using the old index with unupdated cache-tree part
		 * it misses the work we did here, but that is just a
		 * performance penalty and not a big deal.
		 */
	}

	if (prefix) {
		struct cache_tree *subtree =
			cache_tree_find(active_cache_tree, prefix);
		if (!subtree)
			return WRITE_TREE_PREFIX_ERROR;
		hashcpy(sha1, subtree->sha1);
	}
	else
		hashcpy(sha1, active_cache_tree->sha1);

	if (0 <= newfd)
		rollback_lock_file(lock_file);

	return 0;
}

static int commit_index_files(void)
{
	int err = 0;

	switch (commit_style) {
	case COMMIT_AS_IS:
		break; /* nothing to do */
	case COMMIT_NORMAL:
		err = commit_lock_file(&index_lock);
		break;
	case COMMIT_PARTIAL:
		err = commit_lock_file(&index_lock);
		rollback_lock_file(&false_lock);
		break;
	}

	return err;
}

struct ref *fetch_pack(struct fetch_pack_args *my_args,
		       int fd[], struct child_process *conn,
		       const struct ref *ref,
		const char *dest,
		int nr_heads,
		char **heads,
		char **pack_lockfile)
{
	struct stat st;
	struct ref *ref_cpy;

	fetch_pack_setup();
	memcpy(&args, my_args, sizeof(args));
	if (args.depth > 0) {
		if (stat(git_path("shallow"), &st))
			st.st_mtime = 0;
	}

	if (heads && nr_heads)
		nr_heads = remove_duplicates(nr_heads, heads);
	if (!ref) {
		packet_flush(fd[1]);
		die("no matching remote head");
	}
	ref_cpy = do_fetch_pack(fd, ref, nr_heads, heads, pack_lockfile);

	if (args.depth > 0) {
		struct cache_time mtime;
		char *shallow = git_path("shallow");
		int fd;

		mtime.sec = st.st_mtime;
#ifdef USE_NSEC
		mtime.usec = st.st_mtim.usec;
#endif
		if (stat(shallow, &st)) {
			if (mtime.sec)
				die("shallow file was removed during fetch");
		} else if (st.st_mtime != mtime.sec
#ifdef USE_NSEC
				|| st.st_mtim.usec != mtime.usec
#endif
			  )
			die("shallow file was changed during fetch");

		fd = hold_lock_file_for_update(&lock, shallow, 1);
		if (!write_shallow_commits(fd, 0)) {
			unlink(shallow);
			rollback_lock_file(&lock);
		} else {
			commit_lock_file(&lock);
		}
	}

	reprepare_packed_git();
	return ref_cpy;
}

static void rewrite_credential_file(const char *fn, struct credential *c,
				    struct strbuf *extra)
{
	if (hold_lock_file_for_update(&credential_lock, fn, 0) < 0)
		die_errno("unable to get credential storage lock");
	if (extra)
		print_line(extra);
	parse_credential_file(fn, c, NULL, print_line);
	if (commit_lock_file(&credential_lock) < 0)
		die_errno("unable to commit credential store");
}

static void write_message(struct strbuf *msgbuf, const char *filename)
{
	static struct lock_file msg_file;

	int msg_fd = hold_lock_file_for_update(&msg_file, filename,
					       LOCK_DIE_ON_ERROR);
	if (write_in_full(msg_fd, msgbuf->buf, msgbuf->len) < 0)
		die_errno(_("Could not write to %s"), filename);
	strbuf_release(msgbuf);
	if (commit_lock_file(&msg_file) < 0)
		die(_("Error wrapping up %s."), filename);
}

static void save_head(const char *head)
{
	static struct lock_file head_lock;
	struct strbuf buf = STRBUF_INIT;
	int fd;

	fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), LOCK_DIE_ON_ERROR);
	strbuf_addf(&buf, "%s\n", head);
	if (write_in_full(fd, buf.buf, buf.len) < 0)
		die_errno(_("Could not write to %s"), git_path_head_file());
	if (commit_lock_file(&head_lock) < 0)
		die(_("Error wrapping up %s."), git_path_head_file());
}

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);
}

int create_bundle(struct bundle_header *header, const char *path,
		  int argc, const char **argv)
{
	static struct lock_file lock;
	int bundle_fd = -1;
	int bundle_to_stdout;
	int ref_count = 0;
	struct rev_info revs;

	bundle_to_stdout = !strcmp(path, "-");
	if (bundle_to_stdout)
		bundle_fd = 1;
	else
		bundle_fd = hold_lock_file_for_update(&lock, path,
						      LOCK_DIE_ON_ERROR);

	/* write signature */
	write_or_die(bundle_fd, bundle_signature, strlen(bundle_signature));

	/* init revs to list objects for pack-objects later */
	save_commit_buffer = 0;
	init_revisions(&revs, NULL);

	/* write prerequisites */
	if (compute_and_write_prerequisites(bundle_fd, &revs, argc, argv))
		return -1;

	argc = setup_revisions(argc, argv, &revs, NULL);

	if (argc > 1)
		return error(_("unrecognized argument: %s"), argv[1]);

	object_array_remove_duplicates(&revs.pending);

	ref_count = write_bundle_refs(bundle_fd, &revs);
	if (!ref_count)
		die(_("Refusing to create empty bundle."));
	else if (ref_count < 0)
		return -1;

	/* write pack */
	if (write_pack_data(bundle_fd, &lock, &revs))
		return -1;

	if (!bundle_to_stdout) {
		if (commit_lock_file(&lock))
			die_errno(_("cannot create '%s'"), path);
	}
	return 0;
}

static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
{
	static struct lock_file todo_lock;
	const char *todo_path = get_todo_path(opts);
	int next = todo_list->current, offset, fd;

	fd = hold_lock_file_for_update(&todo_lock, todo_path, 0);
	if (fd < 0)
		return error_errno(_("could not lock '%s'"), todo_path);
	offset = next < todo_list->nr ?
		todo_list->items[next].offset_in_buf : todo_list->buf.len;
	if (write_in_full(fd, todo_list->buf.buf + offset,
			todo_list->buf.len - offset) < 0)
		return error_errno(_("could not write to '%s'"), todo_path);
	if (commit_lock_file(&todo_lock) < 0)
		return error(_("failed to finalize '%s'."), todo_path);
	return 0;
}

static int write_pseudoref(const char *pseudoref, const unsigned char *sha1,
			   const unsigned char *old_sha1, struct strbuf *err)
{
	const char *filename;
	int fd;
	static struct lock_file lock;
	struct strbuf buf = STRBUF_INIT;
	int ret = -1;

	strbuf_addf(&buf, "%s\n", sha1_to_hex(sha1));

	filename = git_path("%s", pseudoref);
	fd = hold_lock_file_for_update(&lock, filename, LOCK_DIE_ON_ERROR);
	if (fd < 0) {
		strbuf_addf(err, "could not open '%s' for writing: %s",
			    filename, strerror(errno));
		return -1;
	}

	if (old_sha1) {
		unsigned char actual_old_sha1[20];

		if (read_ref(pseudoref, actual_old_sha1))
			die("could not read ref '%s'", pseudoref);
		if (hashcmp(actual_old_sha1, old_sha1)) {
			strbuf_addf(err, "unexpected sha1 when writing '%s'", pseudoref);
			rollback_lock_file(&lock);
			goto done;
		}
	}

	if (write_in_full(fd, buf.buf, buf.len) != buf.len) {
		strbuf_addf(err, "could not write to '%s'", filename);
		rollback_lock_file(&lock);
		goto done;
	}

	commit_lock_file(&lock);
	ret = 0;
done:
	strbuf_release(&buf);
	return ret;
}

static void save_todo(struct commit_list *todo_list, struct replay_opts *opts)
{
	static struct lock_file todo_lock;
	struct strbuf buf = STRBUF_INIT;
	int fd;

	fd = hold_lock_file_for_update(&todo_lock, git_path_todo_file(), LOCK_DIE_ON_ERROR);
	if (format_todo(&buf, todo_list, opts) < 0)
		die(_("Could not format %s."), git_path_todo_file());
	if (write_in_full(fd, buf.buf, buf.len) < 0) {
		strbuf_release(&buf);
		die_errno(_("Could not write to %s"), git_path_todo_file());
	}
	if (commit_lock_file(&todo_lock) < 0) {
		strbuf_release(&buf);
		die(_("Error wrapping up %s."), git_path_todo_file());
	}
	strbuf_release(&buf);
}

static int write_rr(struct string_list *rr, int out_fd)
{
	int i;
	for (i = 0; i < rr->nr; i++) {
		const char *path;
		int length;
		if (!rr->items[i].util)
			continue;
		path = rr->items[i].string;
		length = strlen(path) + 1;
		if (write_in_full(out_fd, rr->items[i].util, 40) != 40 ||
		    write_str_in_full(out_fd, "\t") != 1 ||
		    write_in_full(out_fd, path, length) != length)
			die("unable to write rerere record");
	}
	if (commit_lock_file(&write_lock) != 0)
		die("unable to write rerere record");
	return 0;
}

static int save_head(const char *head)
{
	static struct lock_file head_lock;
	struct strbuf buf = STRBUF_INIT;
	int fd;

	fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), 0);
	if (fd < 0) {
		rollback_lock_file(&head_lock);
		return error_errno(_("could not lock HEAD"));
	}
	strbuf_addf(&buf, "%s\n", head);
	if (write_in_full(fd, buf.buf, buf.len) < 0) {
		rollback_lock_file(&head_lock);
		return error_errno(_("could not write to '%s'"),
				   git_path_head_file());
	}
	if (commit_lock_file(&head_lock) < 0) {
		rollback_lock_file(&head_lock);
		return error(_("failed to finalize '%s'."), git_path_head_file());
	}
	return 0;
}