vsock: enable setting SO_ZEROCOPY

For AF_VSOCK, zerocopy tx mode depends on transport, so this option must
be set in AF_VSOCK implementation where transport is accessible (if
transport is not set during setting SO_ZEROCOPY: for example socket is
not connected, then SO_ZEROCOPY will be enabled, but once transport will
be assigned, support of this type of transmission will be checked).

To handle SO_ZEROCOPY, AF_VSOCK implementation uses SOCK_CUSTOM_SOCKOPT
bit, thus handling SOL_SOCKET option operations, but all of them except
SO_ZEROCOPY will be forwarded to the generic handler by calling
'sock_setsockopt()'.

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

net/vmw_vsock/af_vsock.c

···
 			goto out;
 		}
 
-		if (vsock_msgzerocopy_allow(transport))
+		if (vsock_msgzerocopy_allow(transport)) {
 			set_bit(SOCK_SUPPORT_ZC, &sk->sk_socket->flags);
+		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
+			/* If this option was set before 'connect()',
+			 * when transport was unknown, check that this
+			 * feature is supported here.
+			 */
+			err = -EOPNOTSUPP;
+			goto out;
+		}
 
 		err = vsock_auto_bind(vsk);
 		if (err)
···
 	const struct vsock_transport *transport;
 	u64 val;
 
-	if (level != AF_VSOCK)
+	if (level != AF_VSOCK && level != SOL_SOCKET)
 		return -ENOPROTOOPT;
 
 #define COPY_IN(_v)                                       \
···
 	lock_sock(sk);
 
 	transport = vsk->transport;
+
+	if (level == SOL_SOCKET) {
+		int zerocopy;
+
+		if (optname != SO_ZEROCOPY) {
+			release_sock(sk);
+			return sock_setsockopt(sock, level, optname, optval, optlen);
+		}
+
+		/* Use 'int' type here, because variable to
+		 * set this option usually has this type.
+		 */
+		COPY_IN(zerocopy);
+
+		if (zerocopy < 0 || zerocopy > 1) {
+			err = -EINVAL;
+			goto exit;
+		}
+
+		if (transport && !vsock_msgzerocopy_allow(transport)) {
+			err = -EOPNOTSUPP;
+			goto exit;
+		}
+
+		sock_valbool_flag(sk, SOCK_ZEROCOPY, zerocopy);
+		goto exit;
+	}
 
 	switch (optname) {
 	case SO_VM_SOCKETS_BUFFER_SIZE:
···
 			return ret;
 		}
 	}
+
+	/* SOCK_DGRAM doesn't have 'setsockopt' callback set in its
+	 * proto_ops, so there is no handler for custom logic.
+	 */
+	if (sock_type_connectible(sock->type))
+		set_bit(SOCK_CUSTOM_SOCKOPT, &sk->sk_socket->flags);
 
 	vsock_insert_unbound(vsk);