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. 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? Thanks, Arseniy > >> >> Page 1802 (description of 'send()' call): >> MSG_NOSIGNAL >> >> 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 >> returned >> >> And the same for 'sendto()' and 'sendmsg()' >> >> Link to the POSIX document: >> https://www.open-std.org/jtc1/sc22/open/n4217.pdf >> >> 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? > > Thanks, > Stefano >
