sctp: add support for busy polling to sctp protocol

The busy polling socket option adds support for sockets to busy wait on data
arriving on the napi queue from which they have most recently received a frame.
Currently only tcp and udp support this feature, but theres no reason sctp can't
do so as well.  Add it in so appliations can take advantage of it

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Vlad Yasevich <vyasevich@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Daniel Borkmann <dborkman@redhat.com>
CC: netdev@vger.kernel.org
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -71,6 +71,7 @@
 #include <net/route.h>
 #include <net/ipv6.h>
 #include <net/inet_common.h>
+#include <net/busy_poll.h>
 
 #include <linux/socket.h> /* for sa_family_t */
 #include <linux/export.h>
@@ -6557,6 +6558,10 @@ static struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags,
 		if (sk->sk_shutdown & RCV_SHUTDOWN)
 			break;
 
+		if (sk_can_busy_loop(sk) &&
+		    sk_busy_loop(sk, noblock))
+			continue;
+
 		/* User doesn't want to wait.  */
 		error = -EAGAIN;
 		if (!timeo)

net/sctp/ulpqueue.c

@@ -38,6 +38,7 @@
 #include <linux/types.h>
 #include <linux/skbuff.h>
 #include <net/sock.h>
+#include <net/busy_poll.h>
 #include <net/sctp/structs.h>
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>
@@ -204,6 +205,9 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 	if (sock_flag(sk, SOCK_DEAD) || (sk->sk_shutdown & RCV_SHUTDOWN))
 		goto out_free;
 
+	if (!sctp_ulpevent_is_notification(event))
+		sk_mark_napi_id(sk, skb);
+
 	/* Check if the user wishes to receive this event.  */
 	if (!sctp_ulpevent_is_enabled(event, &sctp_sk(sk)->subscribe))
 		goto out_free;