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

Joe Damato
2025-03-21T20:30:47Z

On Fri, Mar 21, 2025 at 09:36:34AM -0700, Joe Damato wrote:
> 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.

I think what added to my confusion here was this bit, Jens:

> > As far as the bit about plumbing only the splice bits, sorry if I'm
> > being dense here, do you mean plumbing the error queue through to
> > splice only and dropping sendfile2?
> >
> > That is an option. Then the apps currently using sendfile could use
> > splice instead and get completion notifications on the error queue.
> > That would probably work and be less work than rewriting to use
> > iouring, but probably a bit more work than using a new syscall.
>
> Yep

I thought I was explicitly asking if adding SPLICE_F_ZC and plumbing
through the error queue notifications was OK and your response here
("Yep") suggested to me that it would be a suitable path to
consider.

I take it from your other responses, though, that I was mistaken.