Re: [RFC PATCH v1 1/2] vsock: send SIGPIPE on write to shutdowned socket

From: Stefano Garzarella
Date: Fri Aug 04 2023 - 10:29:27 EST

On Fri, Aug 04, 2023 at 03:46:47PM +0300, Arseniy Krasnov wrote:
Hi Stefano,

On 02.08.2023 10:46, Stefano Garzarella wrote:
On Tue, Aug 01, 2023 at 05:17:26PM +0300, Arseniy Krasnov wrote:
POSIX requires to send SIGPIPE on write to SOCK_STREAM socket which was
shutdowned with SHUT_WR flag or its peer was shutdowned with SHUT_RD
flag. Also we must not send SIGPIPE if MSG_NOSIGNAL flag is set.

Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
net/vmw_vsock/af_vsock.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 020cf17ab7e4..013b65241b65 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1921,6 +1921,9 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
            err = total_written;
+    if (sk->sk_type == SOCK_STREAM)
+        err = sk_stream_error(sk, msg->msg_flags, err);

Do you know why we don't need this for SOCK_SEQPACKET and SOCK_DGRAM?

Yes, here is my explanation:

This function checks that input error is SIGPIPE, and if so it sends SIGPIPE to the 'current' thread
(except case when MSG_NOSIGNAL flag is set). This behaviour is described in POSIX:

Page 367 (description of defines from sys/socket.h):
MSG_NOSIGNAL: No SIGPIPE generated when an attempt to send is made on a stream-
oriented socket that is no longer connected.

Page 497 (description of SOCK_STREAM):
A SIGPIPE signal is raised if a thread sends on a broken stream (one that is
no longer connected).

Okay, but I think we should do also for SEQPACKET:

In 2.10.6 Socket Types:

"The SOCK_SEQPACKET socket type is similar to the SOCK_STREAM type, and
is also connection-oriented. The only difference between these types is
that record boundaries ..."

Then in 2.10.14 Signals:

"The SIGPIPE signal shall be sent to a thread that attempts to send data
on a socket that is no longer able to send. In addition, the send
operation fails with the error [EPIPE]."

It's honestly not super clear, but I assume the problem is similar with
seqpacket since it's connection-oriented, or did I miss something?

For example in sctp_sendmsg() IIUC we raise a SIGPIPE regardless of
whether the socket is STREAM or SEQPACKET.

Page 1802 (description of 'send()' call):

Requests not to send the SIGPIPE signal if an attempt to
send is made on a stream-oriented socket that is no
longer connected. The [EPIPE] error shall still be

And the same for 'sendto()' and 'sendmsg()'

Link to the POSIX document:

TCP (I think we must rely on it), KCM, SMC sockets (all of them are stream) work in the same
way by calling this function. AF_UNIX also works in the same way, but it implements SIGPIPE handling
without this function.

I'm okay calling this function.

The only thing that confused me a little bit, that sockets above returns EPIPE when
we have only SEND_SHUTDOWN set, but for AF_VSOCK EPIPE is returned for RCV_SHUTDOWN
also, but I think it is related to this patchset.

Do you mean that it is NOT related to this patchset?