Re: [PATCH 0/5] Reintroduce writev(3p)
- From
Patrick Steinhardt <ps@pks.im>
- Date
- Aug 6, 2026, 06:28 UTC
- 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:
Show 18 quoted lines
> 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