On Mon, Aug 14, 2023 at 10:46:05PM +0300, Arseniy Krasnov wrote:
On 04.08.2023 17:28, Stefano Garzarella wrote:
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;
}
out:
+ 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:
https://pubs.opengroup.org/onlinepubs/009696699/functions/xsh_chap02_10.html
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.
Update about sending SIGPIPE for SOCK_SEQPACKET, I checked POSIX doc and kernel sources more deeply:
1)
I checked four types of sockets, which sends SIGPIPE for SOCK_SEQPACKET or not ('YES' if
this socket sends SIGPIPE in SOCK_SEQPACKET case):
net/kcm/: YES
net/unix/: NO
net/sctp/: YES
net/caif/: NO
Looking for this, I think it is impossible to get the right answer, as there is some
mess - everyone implements it as wish.
Eheh, I had the same impression!
2)
I opened POSIX spec again, and here are details about returning EPIPE from pages
for 'send()', 'sendto()', 'sendmsg()':
[EPIPE] The socket is shut down for writing, or the socket is connection-mode and is
no longer connected. In the latter case, and if the socket is of type
SOCK_STREAM, the SIGPIPE signal is generated to the calling thread
So my opinion is that we need to send SIGPIPE only for SOCK_STREAM. Another question
is how to interpret this from above (but again - SIGPIPE is related for SOCK_STREAM
only):
**" and is no longer connected"**
IIUC, if we follow POSIX strictly, this check must be like:
/* socket is shut down for writing or no longer connected. */
if (sk->sk_shutdown & SEND_SHUTDOWN ||
vsk->peer_shutdown & RCV_SHUTDOWN ||
sock_flag(SOCK_DONE)) {
err = -EPIPE;
goto out;
}
...
out:
/* Handle -EPIPE for stream socket which is no longer connected. */
if (sk->sk_type == SOCK_STREAM &&
sock_flag(SOCK_DONE))
err = sk_stream_error();
From the other side, we can just follow TCP/AF_UNIX implementations as both are
popular types of socket. In this case I suggest to implement this check like
(e.g. without sock_flag(SOCK_DONE)):
if (sk->sk_shutdown & SEND_SHUTDOWN ||
vsk->peer_shutdown & RCV_SHUTDOWN) {
err = -EPIPE;
goto out;
}
...
out:
if (sk->sk_type == SOCK_STREAM)
err = sk_stream_error();
What do you think?
I'd follow TCP/AF_UNIX implementations, but it is up to you ;-)
Thanks,
Stefano
