From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 17 Apr 2008 23:51:39 GMT
Subject: Re: [PATCH 2/8] Add a lockfile function to append to a file
Message-ID: <7vy77ckpkk.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <alpine.LNX.1.00.0804171931480.19665@iabervon.org>

Daniel Barkalow <barkalow@iabervon.org> writes:

> +int hold_lock_file_for_append(struct lock_file *lk, const char *path, int die_on_error)
> +{
> +	int fd = lock_file(lk, path);
> +	struct stat st;
> +	if (!stat(path, &st)) {
> +		int orig_fd = open(path, O_RDONLY);
> +		size_t mmap_size = xsize_t(st.st_size);
> +		void *mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE,
> +				   orig_fd, 0);
> +		write_or_die(fd, mmap, mmap_size);
> +		munmap(mmap, mmap_size);
> +	}
> +	if (fd < 0 && die_on_error)
> +		die("unable to create '%s.lock': %s", path, strerror(errno));
> +	return fd;
> +}

Another glitch.  What should we do when stat(path) fails but the file
cannot be read?

I think the sequence actually should be:

	fd = lock_file();
        if (fd < 0)
        	error out;
	orig_fd = open(path, O_RDONLY);
        if (orig_fd < 0) {
		if (errno != ENOENT)
			die("unable to open %s", path);
		copy;
	}
	return fd;