update-index: do not die too early in a read-only repository.

This delays the error exit from hold_lock_file_for_update() in
update-index, so that "update-index --refresh" in a read-only
repository can still report what paths are stat-dirty before
exiting.

Also it makes -q to squelch the error message.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

builtin-update-index.c

@@ -486,6 +486,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	int prefix_length = prefix ? strlen(prefix) : 0;
 	char set_executable_bit = 0;
 	unsigned int refresh_flags = 0;
+	int lock_error = 0;
 	struct lock_file *lock_file;
 
 	git_config(git_default_config);
@@ -493,7 +494,9 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	/* 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_lock_file_for_update(lock_file, get_index_file(), 1);
+	newfd = hold_lock_file_for_update(lock_file, get_index_file(), 0);
+	if (newfd < 0)
+		lock_error = errno;
 
 	entries = read_cache();
 	if (entries < 0)
@@ -650,6 +653,12 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 
  finish:
 	if (active_cache_changed) {
+		if (newfd < 0) {
+			if (refresh_flags & REFRESH_QUIET)
+				exit(128);
+			die("unable to create '%s.lock': %s",
+			    get_index_file(), strerror(lock_error));
+		}
 		if (write_cache(newfd, active_cache, active_nr) ||
 		    close(newfd) || commit_lock_file(lock_file))
 			die("Unable to write new index file");