netdev - Re: [PATCH 0/5] add initial io_uring

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Date:   Thu, 6 Apr 2023 08:59:53 -0700
From:   Breno Leitao <leitao@...ian.org>
To:     Willem de Bruijn <willemb@...gle.com>
Cc:     io-uring@...r.kernel.org, netdev@...r.kernel.org, kuba@...nel.org,
        asml.silence@...il.com, axboe@...nel.dk, leit@...com,
        edumazet@...gle.com, pabeni@...hat.com, davem@...emloft.net,
        dccp@...r.kernel.org, mptcp@...ts.linux.dev,
        linux-kernel@...r.kernel.org, dsahern@...nel.org,
        willemdebruijn.kernel@...il.com, matthieu.baerts@...sares.net,
        marcelo.leitner@...il.com
Subject: Re: [PATCH 0/5] add initial io_uring_cmd support for sockets

On Thu, Apr 06, 2023 at 11:34:28AM -0400, Willem de Bruijn wrote:
> On Thu, Apr 6, 2023 at 10:45 AM Breno Leitao <leitao@...ian.org> wrote:
> >
> > From: Breno Leitao <leit@...com>
> >
> > This patchset creates the initial plumbing for a io_uring command for
> > sockets.
> >
> > For now, create two uring commands for sockets, SOCKET_URING_OP_SIOCOUTQ
> > and SOCKET_URING_OP_SIOCINQ. They are similar to ioctl operations
> > SIOCOUTQ and SIOCINQ. In fact, the code on the protocol side itself is
> > heavily based on the ioctl operations.
> 
> This duplicates all the existing ioctl logic of each protocol.
> 
> Can this just call the existing proto_ops.ioctl internally and translate from/to
> io_uring format as needed?

This is doable, and we have two options in this case:

1) Create a ioctl core function that does not call `put_user()`, and
call it from both the `udp_ioctl` and `udp_uring_cmd`, doing the proper
translations. Something as:

	int udp_ioctl_core(struct sock *sk, int cmd, unsigned long arg)
	{
		int amount;
		switch (cmd) {
		case SIOCOUTQ: {
			amount = sk_wmem_alloc_get(sk);
			break;
		}
		case SIOCINQ: {
			amount = max_t(int, 0, first_packet_length(sk));
			break;
		}
		default:
			return -ENOIOCTLCMD;
		}
		return amount;
	}

	int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
	{
		int amount = udp_ioctl_core(sk, cmd, arg);

		return put_user(amount, (int __user *)arg);
	}
	EXPORT_SYMBOL(udp_ioctl);


2) Create a function for each "case entry". This seems a bit silly for
UDP, but it makes more sense for other protocols. The code will look
something like:

	 int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
	 {
		switch (cmd) {
		case SIOCOUTQ:
		{
			int amount = udp_ioctl_siocoutq();
			return put_user(amount, (int __user *)arg);
		}
		...
	  }

What is the best approach?