Re: [PATCH] entry: check for fstat() errors after checkout

From: Junio C Hamano <gitster@pobox.com>
To: Matheus Tavares Bernardino <matheus.bernardino@usp.br>
Cc: git <git@vger.kernel.org>, Derrick Stolee <stolee@gmail.com>
Subject: Re: [PATCH] entry: check for fstat() errors after checkout
Date: Tue, 21 Jul 2020 13:00:30 -0700	[thread overview]
Message-ID: <xmqq1rl48wpt.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <CAHd-oW4_A7JRmdTqCMrDU7b6-PqBSpNVD-csm3y9Bype6Vn9rA@mail.gmail.com> (Matheus Tavares Bernardino's message of "Tue, 21 Jul 2020 12:39:13 -0300")

Matheus Tavares Bernardino <matheus.bernardino@usp.br> writes:

> I was looking further at this code and noticed that the conditions
> under which we fstat() (or lstat()) an entry are slightly different
> throughout entry.c:
>
> - In write_entry()'s footer, we call lstat() iff stat->refresh_cache.
> - In write_entry()'s `write_file_entry` label, we call fstat_output()
> when !to_tempfile.
> - In streaming_write_entry() we call fstat_output() without checking
> if !to_tempfile.
> - And, finally, in fstat_output() itself, we check
> `state->refresh_cache && !state->base_dir_len`.
>
> I understand we always check state->refresh_cache to avoid getting
> stat information we won't really need later, as we are not updating
> the index. But why do we check !to_tempfile and !state->base_dir_len?
> Doesn't writing to a tempfile or using a checkout prefix already imply
> !state->refresh_cache?

You can easily blame the code back to e4c72923 (write_entry(): use
fstat() instead of lstat() when file is open, 2009-02-09).  Back
then, only a single place assigned 0 to state.refresh_cache and that
is in "checkout-index" with either base_dir_len or to_tempfile set.

I do not remember, and I am fairly sure Stolee does not remember
either.  If I have to guess, this was done merely to be extra
cautious, perhaps? As refresh_cache bit is checked first, check for
!to_tempfile and !base_dir_len would be dead at best and redundant
at worst.