On Thu, Oct 27, 2016 at 4:36 PM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
>
> Would the best endgame shape for this function be to open with
> O_NOATIME (and retry without), and then add CLOEXEC with fcntl(2)
> but ignoring an error from it, I guess? That would be the closest
> to what we historically had, I would think.
I think that's the best model.
Note that the O_NOATIME code is very much designed to try O_NOATIME
only _once_. Because even when the kernel supports O_NOATIME, if you
have a shared object tree where you may not be the owner of all the
files, a O_NOATIME open can fail with NOPERM ("You are not allowed to
hide your accesses to this file").
This is why it uses that
static unsigned int sha1_file_open_flag = O_NOATIME;
and if the O_NOATIME open ever fails (and the no-O_NOATIME open
succeeds), it clears that flag. Exactly so that it will *not* end up
in some kind of "let's open and fail and re-open" loop. It's designed
to fail once.
Or at least that's how it used to be originally. This code has
obviously changed since that early design. Now it seems to clear it
for any non-ENOENT error. Which looks fine too.
Linus