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

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Message-ID: <Z9usmpFw7y75eOhk@infradead.org>
Date: Wed, 19 Mar 2025 22:50:18 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Joe Damato <jdamato@...tly.com>, 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 Wed, Mar 19, 2025 at 08:32:19AM -0700, Joe Damato wrote:
> See the docs on MSG_ZEROCOPY [1], but in short when a user app calls
> sendmsg and passes MSG_ZEROCOPY a completion notification is added
> to the error queue. The user app can poll for these to find out when
> the TX has completed and the buffer it passed to the kernel can be
> overwritten.

Yikes.  That's not just an ugly interface, but something entirely
specific to sockets and incompatible with all other asynchronous I/O
interfaces.

> > and why aren't you simply plugging this into io_uring and generate
> > a CQE so that it works like all other asynchronous operations?
> 
> I linked to the iouring work that Pavel did in the cover letter.
> Please take a look.

Please write down what matters in the cover letter, including all the
important tradeoffs.