af_vsock: implement send logic for SEQPACKET

Update current stream enqueue function for SEQPACKET
support:
1) Call transport's seqpacket enqueue callback.
2) Return value from enqueue function is whole record length or error
for SOCK_SEQPACKET.

Signed-off-by: Arseny Krasnov <[e-mail]>
Reviewed-by: Stefano Garzarella <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/af_vsock.h

···
 	/* SEQ_PACKET. */
 	ssize_t (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
 				     int flags);
+	int (*seqpacket_enqueue)(struct vsock_sock *vsk, struct msghdr *msg,
+				 size_t len);
 
 	/* Notification. */
 	int (*notify_poll_in)(struct vsock_sock *, size_t, bool *);

net/vmw_vsock/af_vsock.c

···
 		 * responsibility to check how many bytes we were able to send.
 		 */
 
-		written = transport->stream_enqueue(
-				vsk, msg,
-				len - total_written);
+		if (sk->sk_type == SOCK_SEQPACKET) {
+			written = transport->seqpacket_enqueue(vsk,
+						msg, len - total_written);
+		} else {
+			written = transport->stream_enqueue(vsk,
+					msg, len - total_written);
+		}
 		if (written < 0) {
 			err = -ENOMEM;
 			goto out_err;
···
 	}
 
 out_err:
-	if (total_written > 0)
-		err = total_written;
+	if (total_written > 0) {
+		/* Return number of written bytes only if:
+		 * 1) SOCK_STREAM socket.
+		 * 2) SOCK_SEQPACKET socket when whole buffer is sent.
+		 */
+		if (sk->sk_type == SOCK_STREAM || total_written == len)
+			err = total_written;
+	}
 out:
 	release_sock(sk);
 	return err;