Merge branch 'dt/gc-ignore-old-gc-logs' into maint

A "gc.log" file left by a backgrounded "gc --auto" disables further
automatic gc; it has been taught to run at least once a day (by
default) by ignoring a stale "gc.log" file that is too old.

* dt/gc-ignore-old-gc-logs:
  gc: ignore old gc.log files

Documentation/config.txt

@@ -1402,6 +1402,12 @@ gc.autoDetach::
 	Make `git gc --auto` return immediately and run in background
 	if the system supports it. Default is true.
 
+gc.logExpiry::
+	If the file gc.log exists, then `git gc --auto` won't run
+	unless that file is more than 'gc.logExpiry' old.  Default is
+	"1.day".  See `gc.pruneExpire` for more ways to specify its
+	value.
+
 gc.packRefs::
 	Running `git pack-refs` in a repository renders it
 	unclonable by Git versions prior to 1.5.1.2 over dumb

builtin/gc.c

@@ -33,6 +33,8 @@ static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
 static int detach_auto = 1;
+static unsigned long gc_log_expire_time;
+static const char *gc_log_expire = "1.day.ago";
 static const char *prune_expire = "2.weeks.ago";
 static const char *prune_worktrees_expire = "3.months.ago";
 
@@ -76,11 +78,29 @@ static void git_config_date_string(const char *key, const char **output)
 static void process_log_file(void)
 {
 	struct stat st;
-	if (!fstat(get_lock_file_fd(&log_lock), &st) && st.st_size)
+	if (fstat(get_lock_file_fd(&log_lock), &st)) {
+		/*
+		 * Perhaps there was an i/o error or another
+		 * unlikely situation.  Try to make a note of
+		 * this in gc.log along with any existing
+		 * messages.
+		 */
+		int saved_errno = errno;
+		fprintf(stderr, _("Failed to fstat %s: %s"),
+			get_tempfile_path(&log_lock.tempfile),
+			strerror(saved_errno));
+		fflush(stderr);
 		commit_lock_file(&log_lock);
-	else
+		errno = saved_errno;
+	} else if (st.st_size) {
+		/* There was some error recorded in the lock file */
+		commit_lock_file(&log_lock);
+	} else {
+		/* No error, clean up any old gc.log */
+		unlink(git_path("gc.log"));
 		rollback_lock_file(&log_lock);
 	}
+}
 
 static void process_log_file_at_exit(void)
 {
@@ -113,6 +133,8 @@ static void gc_config(void)
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_date_string("gc.pruneexpire", &prune_expire);
 	git_config_date_string("gc.worktreepruneexpire", &prune_worktrees_expire);
+	git_config_date_string("gc.logexpiry", &gc_log_expire);
+
 	git_config(git_default_config, NULL);
 }
 
@@ -290,19 +312,34 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
 static int report_last_gc_error(void)
 {
 	struct strbuf sb = STRBUF_INIT;
-	int ret;
+	int ret = 0;
+	struct stat st;
+	char *gc_log_path = git_pathdup("gc.log");
 
-	ret = strbuf_read_file(&sb, git_path("gc.log"), 0);
+	if (stat(gc_log_path, &st)) {
+		if (errno == ENOENT)
+			goto done;
+
+		ret = error_errno(_("Can't stat %s"), gc_log_path);
+		goto done;
+	}
+
+	if (st.st_mtime < gc_log_expire_time)
+		goto done;
+
+	ret = strbuf_read_file(&sb, gc_log_path, 0);
 	if (ret > 0)
-		return error(_("The last gc run reported the following. "
+		ret = error(_("The last gc run reported the following. "
 			       "Please correct the root cause\n"
 			       "and remove %s.\n"
 			       "Automatic cleanup will not be performed "
 			       "until the file is removed.\n\n"
 			       "%s"),
-			     git_path("gc.log"), sb.buf);
+			    gc_log_path, sb.buf);
 	strbuf_release(&sb);
-	return 0;
+done:
+	free(gc_log_path);
+	return ret;
 }
 
 static int gc_before_repack(void)
@@ -349,7 +386,10 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	argv_array_pushl(&prune_worktrees, "worktree", "prune", "--expire", NULL);
 	argv_array_pushl(&rerere, "rerere", "gc", NULL);
 
+	/* default expiry time, overwritten in gc_config */
 	gc_config();
+	if (parse_expiry_date(gc_log_expire, &gc_log_expire_time))
+		die(_("Failed to parse gc.logexpiry value %s"), gc_log_expire);
 
 	if (pack_refs < 0)
 		pack_refs = !is_bare_repository();
@@ -448,5 +488,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		warning(_("There are too many unreachable loose objects; "
 			"run 'git prune' to remove them."));
 
+	if (!daemonized)
+		unlink(git_path("gc.log"));
+
 	return 0;
 }

t/t6500-gc.sh

@@ -67,5 +67,20 @@ test_expect_success 'auto gc with too many loose objects does not attempt to cre
 	test_line_count = 2 new # There is one new pack and its .idx
 '
 
+test_expect_success 'background auto gc does not run if gc.log is present and recent but does if it is old' '
+	test_commit foo &&
+	test_commit bar &&
+	git repack &&
+	test_config gc.autopacklimit 1 &&
+	test_config gc.autodetach true &&
+	echo fleem >.git/gc.log &&
+	test_must_fail git gc --auto 2>err &&
+	test_i18ngrep "^error:" err &&
+	test_config gc.logexpiry 5.days &&
+	test-chmtime =-345600 .git/gc.log &&
+	test_must_fail git gc --auto &&
+	test_config gc.logexpiry 2.days &&
+	git gc --auto
+'
 
 test_done