Re: [PATCH/RFC v3 7/9] write_entry(): use fstat() instead of lstat() when file is open

[Johannes Sixt <j.sixt@viscovery.net>]

Kjetil Barvik schrieb:
> Currently inside write_entry() we do an lstat(path, &st) call on a
> file which have just been opened inside the exact same function.  It
> should be better to call fstat(fd, &st) on the file while it is open,
> and it should be at least as fast as the lstat() method.
...
> @@ -145,6 +146,11 @@ static int write_entry(struct cache_entry *ce, char *path, const struct checkout
>  		}
>  
>  		wrote = write_in_full(fd, new, size);
> +		/* use fstat() only when path == ce->name */
> +		if (state->refresh_cache && !to_tempfile && !state->base_dir_len) {
> +			fstat(fd, &st);
> +			fstat_done = 1;
> +		}
>  		close(fd);

I've a bad gut feeling about this: It may not work as expected on Windows
because there is this statement in the documentation:

  "The only guarantee about a file timestamp is that the file time is
   correctly reflected when the handle that makes the change is closed."

(http://msdn.microsoft.com/en-us/library/ms724290(VS.85).aspx)

We are operating on a temporary file. It could happen that the fstat()
returns the time when the file was created, as opposed to when the
write_in_full() was completed successfully. The fstat()ed time ends up in
the index, but it can be different from what later lstat() calls report
(and the file would be regarded as modified).

I have the suspicion that the gain from this patch is minimal. Would you
mind playing it safe and drop this patch?

-- Hannes