Re: [PATCH 2/2] A loose object is not corrupt if it cannot be read due to EMFILE

From: Erik Faye-Lund <kusmabite@gmail.com>
Date: Nov 18, 2010, 18:18 UTC
Message-ID: <AANLkTi=rrcc5tia03K-Rtqs3vyjOv9P1NArnmbYhCQ27@mail.gmail.com>
In-Reply-To: <20101118172920.GC16610@burratino>

On Thu, Nov 18, 2010 at 6:29 PM, Jonathan Nieder <jrnieder@gmail.com> wrote:

Show 9 quoted lines

> Erik Faye-Lund wrote:
>
>> I was wondering about the same thing, I don't think this approach is
>> very easy to follow. But either way I think we should make sure
>> opendir/closedir/readdir doesn't mess with errno.
>
> Other platforms and are allowed to (and do) clobber errno in many
> non-error situations, so the main effect would be to work around/hide
> some git bugs.

I don't think that's the case; K&R (section B1.7) says "In addition, the integer expression errno (declared in <errno.h>) may contain an error number that contains information about the most recent error.". A non-error condition would not be information about the most recent error. I interpret the use of the word "may" to mean "some functions does not update errno, so errno could also have information about older errors" not as "some functions can clear errno", but other might disagree with me.

POSIX (which defines opendir) says "No function in this volume of IEEE Std 1003.1-2001 shall set errno to 0", so I think it's clear cut in this case. (see http://www.opengroup.org/onlinepubs/009695399/functions/errno.html for the full text)

We also seem to depend quite heavily on errno being preserved on non-errors some places around in the code.