Subject: Re: [PATCH] sequencer: rewrite save_head() in terms of write_message()

From: Junio C Hamano <[email-masked]>
Date: Fri, 24 Mar 2023 08:01:12 -0700

Oswald Buddenhagen <[email-masked]> writes:

> Saves some code duplication.

There are two and a half small behaviour changes, but I think it is
a good change overall.

 - We used to fail with "could not lock HEAD", but now we give the
   real filename for "sequencer/head", when the locking fails.

 - We used to write the file in a single write_in_full() call, which
   in practice would have been done in a single write() system call.
   Now we do it in two steps, the body of the line in one, and a
   single terminating LF in another.  Also, there is a new error
   mode (object name gets written successfully but writing the
   terminating LF fails) with a new error message.

The former is definite improvement that may help debugging when
things go wrong.  The latter should not be measurable. The new error
mode probably is not noticeable in practice.

Looking good.  Will queue.  Thanks.

> Signed-off-by: Oswald Buddenhagen <[email-masked]>
> ---
>  sequencer.c | 20 +-------------------
>  1 file changed, 1 insertion(+), 19 deletions(-)
>
> diff --git a/sequencer.c b/sequencer.c
> index 3be23d7ca2..ff985fb2e9 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -3187,25 +3187,7 @@ static int create_seq_dir(struct repository *r)
>  
>  static int save_head(const char *head)
>  {
> -	struct lock_file head_lock = LOCK_INIT;
> -	struct strbuf buf = STRBUF_INIT;
> -	int fd;
> -	ssize_t written;
> -
> -	fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), 0);
> -	if (fd < 0)
> -		return error_errno(_("could not lock HEAD"));
> -	strbuf_addf(&buf, "%s\n", head);
> -	written = write_in_full(fd, buf.buf, buf.len);
> -	strbuf_release(&buf);
> -	if (written < 0) {
> -		error_errno(_("could not write to '%s'"), git_path_head_file());
> -		rollback_lock_file(&head_lock);
> -		return -1;
> -	}
> -	if (commit_lock_file(&head_lock) < 0)
> -		return error(_("failed to finalize '%s'"), git_path_head_file());
> -	return 0;
> +	return write_message(head, strlen(head), git_path_head_file(), 1);
>  }
>  
>  static int rollback_is_safe(void)