From: Patrick Steinhardt <ps@pks.im>
Date: Thu, 06 Aug 2026 06:28:50 GMT
Subject: Re: [PATCH 0/5] Reintroduce writev(3p)
Message-ID: <anQpop92SCAA2C9z@pks.im>
In-Reply-To: <xmqqa4r0payv.fsf@gitster.g>

On Wed, Aug 05, 2026 at 01:29:44PM -0700, Junio C Hamano wrote:
> Johannes Sixt <j6t@kdbg.org> writes:
> 
> > Am 05.08.26 um 20:40 schrieb Junio C Hamano:
> >> I think it is OK to explicitly document that any writev(2) emulation
> >> is allowed to be non-atomic, and it is also OK to declare that using
> >> writev(2) in this application to allow competing writes to the same
> >> destination is a bug.
> >
> > These are fine.
> >
> > But I'm not worried about current uses of writev, I'm worried about
> > future uses: "Look, we already use writev elsewhere. Let's use it here,
> > too, where we can take adavantage of the atomicity of the write." It's
> > too easy to miss a note about non-atomic emulations when the function
> > name advertises more than can be guaranteed. For this reason, I strongly
> > suggest to use a different name.
> 
> That is why I added the "it is also OK to declare" in the above.

We could of course trivially restore the non-interleaving property by
only ever writing the first iovec. POSIX doesn't guarantee that the full
iovec is being written, and write(3p) is already non-interleaving. It
wouldn't even be less efficient compared to the current implementation,
as we have to loop around write(3p) anyway in our compatibility wrapper.

Patrick