vsock: check for MSG_ZEROCOPY support on send

This feature totally depends on transport, so if transport doesn't
support it, return error.
Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/af_vsock.h

@@ -177,6 +177,9 @@ struct vsock_transport {
 
 	/* Read a single skb */
 	int (*read_skb)(struct vsock_sock *, skb_read_actor_t);
+
+	/* Zero-copy. */
+	bool (*msgzerocopy_allow)(void);
 };
 
 /**** CORE ****/
@@ -241,4 +244,8 @@ static inline void __init vsock_bpf_build_proto(void)
 {}
 #endif
 
+static inline bool vsock_msgzerocopy_allow(const struct vsock_transport *t)
+{
+	return t->msgzerocopy_allow && t->msgzerocopy_allow();
+}
 #endif /* __AF_VSOCK_H__ */

net/vmw_vsock/af_vsock.c

@@ -1824,6 +1824,12 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
 		goto out;
 	}
 
+	if (msg->msg_flags & MSG_ZEROCOPY &&
+	    !vsock_msgzerocopy_allow(transport)) {
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
 	/* Wait for room in the produce queue to enqueue our user's data. */
 	timeout = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);