Re: [PATCH 1/3] net: Remove support for AIO on sockets

Re: [PATCH 1/3] net: Remove support for AIO on sockets

[Christoph Hellwig]

On Sat, May 23, 2026 at 03:43:02PM -0400, Demi Marie Obenour via B4 Relay wrote:
> From: Demi Marie Obenour <demiobenour@gmail.com>
> 
> The only user of msg->msg_iocb was AF_ALG, but that's deprecated.
> It can be removed entirely at the cost of only supporting synchronous
> operations.  This doesn't break userspace, which will silently block
> (for a bounded amount of time) in io_submit instead of operating
> asynchronously.
> 
> This also makes struct msghdr smaller, helping every other caller of
> sendmsg().

So we just had a discussion at LLC about how networking needs to support
AIO better for zero copy.

The current TCP zerocopy implementation provides completion notification
through the socket error code, which is freaking weird and doesn't
integrate well with either io_uring or in-kernel callers.

So we really want to pass the iocb down into networking and have it
call ki_complete on completion, with something higher up in the stack
adding that to the error queue for the legacy user interface.

Now I'm not sure if we wouldn't be better off passing that iocb
explicitly instead of in a weird hidden way, but this seemed like
a good place to bring this up.

Re: [PATCH 1/3] net: Remove support for AIO on sockets

[Jens Axboe]

On 5/25/26 2:03 AM, Christoph Hellwig wrote:
> On Sat, May 23, 2026 at 03:43:02PM -0400, Demi Marie Obenour via B4 Relay wrote:
>> From: Demi Marie Obenour <demiobenour@gmail.com>
>>
>> The only user of msg->msg_iocb was AF_ALG, but that's deprecated.
>> It can be removed entirely at the cost of only supporting synchronous
>> operations.  This doesn't break userspace, which will silently block
>> (for a bounded amount of time) in io_submit instead of operating
>> asynchronously.
>>
>> This also makes struct msghdr smaller, helping every other caller of
>> sendmsg().
> 
> So we just had a discussion at LLC about how networking needs to support
> AIO better for zero copy.
> 
> The current TCP zerocopy implementation provides completion notification
> through the socket error code, which is freaking weird and doesn't
> integrate well with either io_uring or in-kernel callers.

We already have that via io_uring, and without needing msg_kiocb or the
(very) weird socket error code retrieving.

-- 
Jens Axboe

Re: [PATCH 1/3] net: Remove support for AIO on sockets

[Christoph Hellwig]

On Tue, May 26, 2026 at 09:58:27AM -0600, Jens Axboe wrote:
> > The current TCP zerocopy implementation provides completion notification
> > through the socket error code, which is freaking weird and doesn't
> > integrate well with either io_uring or in-kernel callers.
> 
> We already have that via io_uring

Where?  And how do make that available to in-kernel users like
storage protocols and network file system, which really suffer from
the current MSG_SPLICE_PAGES semantics.

> , and without needing msg_kiocb or the

What do you think is the downside of using a kiocb here like for
everything else with async notifications?