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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
Previous: Junio C HamanoNext: Junio C Hamano
Message 19 of 27 in “Reintroduce writev(3p)”
  1. 0/5 Reintroduce writev(3p)Patrick Steinhardt, Jul 16, 2026
  2. 1/5 compat/posix: introduce writev(3p) wrapperPatrick Steinhardt, Jul 16, 2026
  3. Simon RichterJul 16, 2026
  4. Junio C HamanoJul 16, 2026
  5. Junio C HamanoJul 16, 2026
  6. Patrick SteinhardtAug 5, 2026
  7. 2/5 wrapper: introduce writev(3p) wrappersPatrick Steinhardt, Jul 16, 2026
  8. 3/5 wrapper: properly handle MAX_IO_SIZE in writev(3p)Patrick Steinhardt, Jul 16, 2026
  9. 4/5 sideband: use writev(3p) to send pktlinesPatrick Steinhardt, Jul 16, 2026
  10. 5/5 fast-import: use writev(3p) to send cat-blob responsesPatrick Steinhardt, Jul 16, 2026
  11. Johannes SixtJul 16, 2026
  12. Junio C HamanoJul 27, 2026
  13. Patrick SteinhardtAug 5, 2026
  14. Junio C HamanoAug 5, 2026
  15. Johannes SixtAug 5, 2026
  16. Junio C HamanoAug 5, 2026
  17. Johannes SixtAug 5, 2026
  18. Junio C HamanoAug 5, 2026
  19. Patrick SteinhardtAug 6, 2026
  20. Junio C HamanoAug 6, 2026
  21. Patrick SteinhardtAug 7, 2026
  22. 0/5 Reintroduce writev(3p)Patrick Steinhardt, Aug 7, 2026
  23. 1/5 compat/posix: introduce writev(3p) wrapperPatrick Steinhardt, Aug 7, 2026
  24. 2/5 wrapper: introduce writev(3p) wrappersPatrick Steinhardt, Aug 7, 2026
  25. 3/5 wrapper: properly handle MAX_IO_SIZE in writev(3p)Patrick Steinhardt, Aug 7, 2026
  26. 4/5 sideband: use writev(3p) to send pktlinesPatrick Steinhardt, Aug 7, 2026
  27. 5/5 fast-import: use writev(3p) to send cat-blob responsesPatrick Steinhardt, Aug 7, 2026

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