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

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Date:   Wed, 29 Jun 2022 09:42:19 +0200
From:   Stefan Metzmacher <metze@...ba.org>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jens Axboe <axboe@...nel.dk>, kernel-team@...com
Subject: Re: [RFC net-next v3 23/29] io_uring: allow to pass addr into sendzc

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?

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?

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.

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.

metze