Split back out update_hook handling in receive-pack

Since we have decided to change the calling conventions for the
pre-receive and post-receive hooks to take the ref data on stdin
rather than on the command line we cannot use the same logic to
invoke the update hook anymore.

So we take a small step backwards towards what we used to have,
and create a specialized function for executing just the update
hook.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

receive-pack.c

@@ -67,7 +67,6 @@ struct command {
 
 static struct command *commands;
 
-static const char update_hook[] = "hooks/update";
 static const char pre_receive_hook[] = "hooks/pre-receive";
 static const char post_receive_hook[] = "hooks/post-receive";
 
@@ -134,6 +133,29 @@ static int run_hook(const char *hook_name,
 	return hook_status(code, hook_name);
 }
 
+static int run_update_hook(struct command *cmd)
+{
+	static const char update_hook[] = "hooks/update";
+	struct child_process proc;
+	const char *argv[5];
+
+	if (access(update_hook, X_OK) < 0)
+		return 0;
+
+	argv[0] = update_hook;
+	argv[1] = cmd->ref_name;
+	argv[2] = sha1_to_hex(cmd->old_sha1);
+	argv[3] = sha1_to_hex(cmd->new_sha1);
+	argv[4] = NULL;
+
+	memset(&proc, 0, sizeof(proc));
+	proc.argv = argv;
+	proc.no_stdin = 1;
+	proc.stdout_to_stderr = 1;
+
+	return hook_status(run_command(&proc), update_hook);
+}
+
 static const char *update(struct command *cmd)
 {
 	const char *name = cmd->ref_name;
@@ -170,7 +192,7 @@ static const char *update(struct command *cmd)
 			return "non-fast forward";
 		}
 	}
-	if (run_hook(update_hook, cmd, 1)) {
+	if (run_update_hook(cmd)) {
 		error("hook declined to update %s", name);
 		return "hook declined";
 	}