Re: [RFC v1] man/man2/close.2: CAVEATS: Document divergence from POSIX.1-2024

[Florian Weimer <fweimer@redhat.com>]

* Vincent Lefevre:

> On 2025-05-16 09:05:47 -0400, Rich Felker wrote:
>> FWIW musl adopted the EINPROGRESS as soon as we were made aware of the
>> issue, and later changed it to returning 0 since applications
>> (particularly, any written prior to this interpretation) are prone to
>> interpret EINPROGRESS as an error condition rather than success and
>> possibly misinterpret it as meaning the fd is still open and valid to
>> pass to close again.
>
> If I understand correctly, this is a poor choice. POSIX.1-2024 says:
>
> ERRORS
>   The close() and posix_close() functions shall fail if:
> [...]
>   [EINPROGRESS]
>     The function was interrupted by a signal and fildes was closed
>     but the close operation is continuing asynchronously.
>
> But this does not mean that the asynchronous close operation will
> succeed.
>
> So the application could incorrectly deduce that the close operation
> was done without any error.

But on Linux, close traditionally has poor error reporting anyway.  You
have to fsync (or equivalent) before calling close if you want error
checking.  On other systems, the fsync is more or less implied by the
close, leading to rather poor performance.

Thanks,
Florian