Re: [RFC net-next v3 23/29] io_uring: allow to pass addr into sendzc

[Pavel Begunkov]

On 6/29/22 08:42, Stefan Metzmacher wrote:
> Hi Pavel,
>
> > +    if (zc->addr) {
> > +        ret = move_addr_to_kernel(zc->addr, zc->addr_len, &address);
> > +        if (unlikely(ret < 0))
> > +            return ret;
> > +        msg.msg_name = (struct sockaddr *)&address;
> > +        msg.msg_namelen = zc->addr_len;
> > +    }
> > +
>
> Given that this fills in msg almost completely can we also have
> a version of SENDMSGZC, it would be very useful to also allow
> msg_control to be passed and as well as an iovec.
>
> Would that be possible?

Right, I left it to follow ups as the series is already too long.

fwiw, I'm going to also add addr to IORING_OP_SEND.


> Do I understand it correctly, that the reason for the new opcode is,
> that IO_OP_SEND would already work with existing MSG_ZEROCOPY behavior, together
> with the recvmsg based completion?

Right, it should work with MSG_ZEROCOPY, but with a different notification
semantics, would need recvmsg from error queues, and with performance
implications.


> In addition I wondering if a completion based on msg_iocb->ki_complete() (indicated by EIOCBQUEUED)
> what have also worked, just deferring the whole sendmsg operation until all buffers are no longer used.
> That way it would be possible to buffers are acked by the remote end when it comes back to the application
> layer.

There is msg_iocb, but it's mostly unused by protocols, IIRC apart
from crypto sockets. And then we'd need to repeat the path of
ubuf_info to handle stuff like skb splitting and perhaps also
changing rules for ->ki_complete


> I'm also wondering if the ki_complete() based approach should always be provided to sock_sendmsg()
> triggered by io_uring (independend of the new zerocopy stuff), it would basically work very simular to
> the uring_cmd() completions, which are able to handle both true async operation indicated by EIOCBQUEUED
> as well as EAGAIN triggered path via io-wq.

Would be even more similar to how we has always been doing
read/write, and rw requests do pass in a msg_iocb, but again,
it's largely ignored internally.

--
Pavel Begunkov