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

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Message-ID: <Z93Mc27xaz5sAo5m@LQ3V64L9R2>
Date: Fri, 21 Mar 2025 13:30:43 -0700
From: Joe Damato <jdamato@...tly.com>
To: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@...radead.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	asml.silence@...il.com, linux-fsdevel@...r.kernel.org,
	edumazet@...gle.com, pabeni@...hat.com, horms@...nel.org,
	linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
	viro@...iv.linux.org.uk, jack@...e.cz, kuba@...nel.org,
	shuah@...nel.org, sdf@...ichev.me, mingo@...hat.com, arnd@...db.de,
	brauner@...nel.org, akpm@...ux-foundation.org, tglx@...utronix.de,
	jolsa@...nel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC -next 00/10] Add ZC notifications to splice and sendfile

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.