[RFC PATCH dlm/next 2/4] dlm: use SHUT_RDWR for SCTP shutdown

[Alexander Aring <aahringo@redhat.com>]

Currently SCTP shutdown() call gets stuck because there is no incoming
EOF indicator on its socket. On the peer side the EOF indicator as
recvmsg() returns 0 will be triggered as mechanism to flush the socket
queue on the receive side. In SCTP recvmsg() function sctp_recvmsg() we
can see that only if sk_shutdown has the bit RCV_SHUTDOWN set SCTP will
recvmsg() will return EOF. The RCV_SHUTDOWN bit will only be set when
shutdown with SHUT_RD is called. We use now SHUT_RDWR to also get a EOF
indicator from recvmsg() call on the shutdown() initiator.

SCTP does not support half closed sockets and the semantic of SHUT_WR is
different here, it seems that calling SHUT_WR on sctp sockets keeps the
socket open to have the possibility to do some specific SCTP operations on
it that we don't do here.

There exists still a difference in the limitations of TCP vs SCTP in
case if we are required to have a half closed socket functionality. This
was tried to archieve with DLM protocol changes in the past and
hopefully we really don't require half closed socket functionality.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/lowcomms.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 50c42b368c83..e4373bce1bc2 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -160,6 +160,7 @@ struct dlm_proto_ops {
 	bool try_new_addr;
 	const char *name;
 	int proto;
+	int how;
 
 	void (*sockopts)(struct socket *sock);
 	int (*bind)(struct socket *sock);
@@ -810,7 +811,7 @@ static void shutdown_connection(struct connection *con, bool and_other)
 		return;
 	}
 
-	ret = kernel_sock_shutdown(con->sock, SHUT_WR);
+	ret = kernel_sock_shutdown(con->sock, dlm_proto_ops->how);
 	up_read(&con->sock_lock);
 	if (ret) {
 		log_print("Connection %p failed to shutdown: %d will force close",
@@ -1858,6 +1859,7 @@ static int dlm_tcp_listen_bind(struct socket *sock)
 static const struct dlm_proto_ops dlm_tcp_ops = {
 	.name = "TCP",
 	.proto = IPPROTO_TCP,
+	.how = SHUT_WR,
 	.sockopts = dlm_tcp_sockopts,
 	.bind = dlm_tcp_bind,
 	.listen_validate = dlm_tcp_listen_validate,
@@ -1896,6 +1898,7 @@ static void dlm_sctp_sockopts(struct socket *sock)
 static const struct dlm_proto_ops dlm_sctp_ops = {
 	.name = "SCTP",
 	.proto = IPPROTO_SCTP,
+	.how = SHUT_RDWR,
 	.try_new_addr = true,
 	.sockopts = dlm_sctp_sockopts,
 	.bind = dlm_sctp_bind,
-- 
2.43.0