netdev - Re: [PATCH for-6.1 1/2] io_uring/net: fail zc send for unsupported protocols

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Date:   Thu, 20 Oct 2022 11:13:50 +0200
From:   Stefan Metzmacher <metze@...ba.org>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, netdev@...r.kernel.org
Subject: Re: [PATCH for-6.1 1/2] io_uring/net: fail zc send for unsupported
 protocols

Hi Pavel,

> If a protocol doesn't support zerocopy it will silently fall back to
> copying. This type of behaviour has always been a source of troubles
> so it's better to fail such requests instead. For now explicitly
> whitelist supported protocols in io_uring, which should be turned later
> into a socket flag.
> 
> Cc: <stable@...r.kernel.org> # 6.0
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>   io_uring/net.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/io_uring/net.c b/io_uring/net.c
> index 8c7226b5bf41..28127f1de1f0 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -120,6 +120,13 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
>   	}
>   }
>   
> +static inline bool io_sock_support_zc(struct socket *sock)
> +{
> +	return likely(sock->sk && sk_fullsock(sock->sk) &&
> +		     (sock->sk->sk_protocol == IPPROTO_TCP ||
> +		      sock->sk->sk_protocol == IPPROTO_UDP));
> +}

Can we please make this more generic (at least for 6.1, which is likely be an lts release)

It means my out of tree smbdirect driver would not be able to provide SENDMSG_ZC.

Currently sk_setsockopt has this logic:

         case SO_ZEROCOPY:
                 if (sk->sk_family == PF_INET || sk->sk_family == PF_INET6) {
                         if (!(sk_is_tcp(sk) ||
                               (sk->sk_type == SOCK_DGRAM &&
                                sk->sk_protocol == IPPROTO_UDP)))
                                 ret = -EOPNOTSUPP;
                 } else if (sk->sk_family != PF_RDS) {
                         ret = -EOPNOTSUPP;
                 }
                 if (!ret) {
                         if (val < 0 || val > 1)
                                 ret = -EINVAL;
                         else
                                 sock_valbool_flag(sk, SOCK_ZEROCOPY, valbool);
                 }
                 break;

Maybe the socket creation code could set
unsigned char skc_so_zerocopy_supported:1;
and/or
unsigned char skc_zerocopy_msg_ubuf_supported:1;

In order to avoid the manual complex tests.

What do you think?

metze