vsock/virtio: add SIOCOUTQ support for all virtio based transports

Introduce support for virtio_transport_unsent_bytes
ioctl for virtio_transport, vhost_vsock and vsock_loopback.

For all transports the unsent bytes counter is incremented
in virtio_transport_get_credit.

In virtio_transport (G2H) and in vhost-vsock (H2G) the counter
is decremented when the skbuff is consumed. In vsock_loopback the
same skbuff is passed from the transmitter to the receiver, so
the counter is decremented before queuing the skbuff to the
receiver.

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

drivers/vhost/vsock.c

···
 					restart_tx = true;
 			}
 
-			consume_skb(skb);
+			virtio_transport_consume_skb_sent(skb, true);
 		}
 	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
 	if (added)
···
 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
+
+		.unsent_bytes             = virtio_transport_unsent_bytes,
 
 		.read_skb = virtio_transport_read_skb,
 	},

include/linux/virtio_vsock.h

···
 	u32 tx_cnt;
 	u32 peer_fwd_cnt;
 	u32 peer_buf_alloc;
+	size_t bytes_unsent;
 
 	/* Protected by rx_lock */
 	u32 fwd_cnt;
···
 s64 virtio_transport_stream_has_data(struct vsock_sock *vsk);
 s64 virtio_transport_stream_has_space(struct vsock_sock *vsk);
 u32 virtio_transport_seqpacket_has_data(struct vsock_sock *vsk);
+
+ssize_t virtio_transport_unsent_bytes(struct vsock_sock *vsk);
+
+void virtio_transport_consume_skb_sent(struct sk_buff *skb,
+				       bool consume);
 
 int virtio_transport_do_socket_init(struct vsock_sock *vsk,
 				 struct vsock_sock *psk);

net/vmw_vsock/virtio_transport.c

···
 
 		virtqueue_disable_cb(vq);
 		while ((skb = virtqueue_get_buf(vq, &len)) != NULL) {
-			consume_skb(skb);
+			virtio_transport_consume_skb_sent(skb, true);
 			added = true;
 		}
 	} while (!virtqueue_enable_cb(vq));
···
 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
+
+		.unsent_bytes             = virtio_transport_unsent_bytes,
 
 		.read_skb = virtio_transport_read_skb,
 	},

net/vmw_vsock/virtio_transport_common.c

···
 }
 EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);
 
+void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
+{
+	struct sock *s = skb->sk;
+
+	if (s && skb->len) {
+		struct vsock_sock *vs = vsock_sk(s);
+		struct virtio_vsock_sock *vvs;
+
+		vvs = vs->trans;
+
+		spin_lock_bh(&vvs->tx_lock);
+		vvs->bytes_unsent -= skb->len;
+		spin_unlock_bh(&vvs->tx_lock);
+	}
+
+	if (consume)
+		consume_skb(skb);
+}
+EXPORT_SYMBOL_GPL(virtio_transport_consume_skb_sent);
+
 u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
 {
 	u32 ret;
···
 	if (ret > credit)
 		ret = credit;
 	vvs->tx_cnt += ret;
+	vvs->bytes_unsent += ret;
 	spin_unlock_bh(&vvs->tx_lock);
 
 	return ret;
···
 
 	spin_lock_bh(&vvs->tx_lock);
 	vvs->tx_cnt -= credit;
+	vvs->bytes_unsent -= credit;
 	spin_unlock_bh(&vvs->tx_lock);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_put_credit);
···
 	kfree(vvs);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_destruct);
+
+ssize_t virtio_transport_unsent_bytes(struct vsock_sock *vsk)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	size_t ret;
+
+	spin_lock_bh(&vvs->tx_lock);
+	ret = vvs->bytes_unsent;
+	spin_unlock_bh(&vvs->tx_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_unsent_bytes);
 
 static int virtio_transport_reset(struct vsock_sock *vsk,
 				  struct sk_buff *skb)

net/vmw_vsock/vsock_loopback.c

···
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
 
+		.unsent_bytes             = virtio_transport_unsent_bytes,
+
 		.read_skb = virtio_transport_read_skb,
 	},
 
···
 	spin_unlock_bh(&vsock->pkt_queue.lock);
 
 	while ((skb = __skb_dequeue(&pkts))) {
+		/* Decrement the bytes_unsent counter without deallocating skb
+		 * It is freed by the receiver.
+		 */
+		virtio_transport_consume_skb_sent(skb, false);
 		virtio_transport_deliver_tap_pkt(skb);
 		virtio_transport_recv_pkt(&loopback_transport, skb);
 	}