netdev - Re: [PATCH net-next] packet: allow MSG

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Date:   Fri, 24 Feb 2023 11:26:27 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     David Lamparter <equinox@...c24.net>, Jens Axboe <axboe@...nel.dk>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next] packet: allow MSG_NOSIGNAL in recvmsg

On Fri, Feb 24, 2023 at 8:18 AM David Lamparter <equinox@...c24.net> wrote:
>
> packet_recvmsg() whitelists a bunch of MSG_* flags, which notably does
> not include MSG_NOSIGNAL.  Unfortunately, io_uring always sets
> MSG_NOSIGNAL, meaning AF_PACKET sockets can't be used in io_uring
> recvmsg().
>
> As AF_PACKET sockets never generate SIGPIPE to begin with, MSG_NOSIGNAL
> is a no-op and can simply be ignored.
>
> Signed-off-by: David Lamparter <equinox@...c24.net>
> Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> ---
>  net/packet/af_packet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

This is odd... I think MSG_NOSIGNAL flag has a meaning for sendmsg()
(or write sides in general)

EPIPE is not supposed to be generated at the receiving side ?

So I would rather make io_uring slightly faster :


diff --git a/io_uring/net.c b/io_uring/net.c
index cbd4b725f58c98e5bc5bf88d5707db5c8302e071..b7f190ca528e6e259eb2b072d7a16aaba98848cb
100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -567,7 +567,7 @@ int io_recvmsg_prep(struct io_kiocb *req, const
struct io_uring_sqe *sqe)
        sr->flags = READ_ONCE(sqe->ioprio);
        if (sr->flags & ~(RECVMSG_FLAGS))
                return -EINVAL;
-       sr->msg_flags = READ_ONCE(sqe->msg_flags) | MSG_NOSIGNAL;
+       sr->msg_flags = READ_ONCE(sqe->msg_flags);
        if (sr->msg_flags & MSG_DONTWAIT)
                req->flags |= REQ_F_NOWAIT;
        if (sr->msg_flags & MSG_ERRQUEUE)