Re: [RFC -next 00/10] Add ZC notifications to splice and sendfile

Joe Damato
2025-03-21T16:36:39Z

On Fri, Mar 21, 2025 at 05:14:59AM -0600, Jens Axboe wrote:
> On 3/20/25 11:56 PM, Christoph Hellwig wrote:
> >> I don't know the entire historical context, but I presume sendmsg
> >> did that because there was no other mechanism at the time.
> >
> > At least aio had been around for about 15 years at the point, but
> > networking folks tend to be pretty insular and reinvent things.
>
> Yep...
>
> >> It seems like Jens suggested that plumbing this through for splice
> >> was a possibility, but sounds like you disagree.
> >
> > Yes, very strongly.
>
> And that is very much not what I suggested, fwiw.

Your earlier message said:

If the answer is "because splice", then it would seem saner to
plumb up those bits only. Would be much simpler too...

wherein I interpreted "plumb those bits" to mean plumbing the error
queue notifications on TX completions.

My sincere apologies that I misunderstood your prior message and/or
misconstrued what you said -- it was not clear to me what you meant.

It is clear to me now, though, that adding a flag to splice as
previously proposed and extending sendfile based on the SO_ZEROCOPY
sock flag being set are both unacceptable solutions.

If you happen to have a suggestion of some piece of code that I
should read (other than the iouring implementation) to inform how I
might build an RFCv2, I would appreciate the pointer.

Thanks for your time and energy,
Joe