Subject: Re: [PATCH] mingw: emulate write(2) that fails with a EPIPE

From: Junio C Hamano <[email-masked]>
Date: Wed, 16 Dec 2015 12:36:21 -0800

Eric Sunshine <[email-masked]> writes:

>> +       if (result < 0 && errno == EINVAL && buf) {
>
> Here, errno is EINVAL...
>
>> +               /* check if fd is a pipe */
>> +               HANDLE h = (HANDLE) _get_osfhandle(fd);
>> +               if (GetFileType(h) == FILE_TYPE_PIPE)
>> +                       errno = EPIPE;
>> +               else
>> +                       errno = EINVAL;
>
> Does any of the code between the outer 'if' and this point clobber
> errno, or are you merely assigning EINVAL for robustness against
> future changes?

I do think it is a good idea to reassign 'errno' here to stress on
the fact that we return EPIPE only when we positively know that we
were reading from a pipe, and otherwise we won't change the original
errno at all.

But at the same time, if other things that are called before we
figure out if we were reading from a pipe could affect errno, I
wonder if that is an indication of a bug--an error return from
system functions that the code is not responding to.  For example,
can _get_osfhandle() fail and when it does what would we see?
Perhaps NULL in h?