vsock/virtio: refactor virtio_transport_send_pkt_work

Preliminary patch to introduce an optimization to the
enqueue system.

All the code used to enqueue a packet into the virtqueue
is removed from virtio_transport_send_pkt_work()
and moved to the new virtio_transport_send_skb() function.
Co-developed-by: Luigi Leonardi <luigi.leonardi@outlook.com>
Signed-off-by: Luigi Leonardi <luigi.leonardi@outlook.com>
Signed-off-by: Marco Pinna <marco.pinn95@gmail.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20240730-pinna-v4-1-5c9179164db5@outlook.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

net/vmw_vsock/virtio_transport.c

@@ -94,33 +94,13 @@ static u32 virtio_transport_get_local_cid(void)
 	return ret;
 }
 
-static void
-virtio_transport_send_pkt_work(struct work_struct *work)
+/* Caller need to hold vsock->tx_lock on vq */
+static int virtio_transport_send_skb(struct sk_buff *skb, struct virtqueue *vq,
+				     struct virtio_vsock *vsock)
 {
-	struct virtio_vsock *vsock =
-		container_of(work, struct virtio_vsock, send_pkt_work);
-	struct virtqueue *vq;
-	bool added = false;
-	bool restart_rx = false;
-
-	mutex_lock(&vsock->tx_lock);
-
-	if (!vsock->tx_run)
-		goto out;
-
-	vq = vsock->vqs[VSOCK_VQ_TX];
-
-	for (;;) {
 	int ret, in_sg = 0, out_sg = 0;
 	struct scatterlist **sgs;
-		struct sk_buff *skb;
-		bool reply;
-
-		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
-		if (!skb)
-			break;
 
-		reply = virtio_vsock_skb_reply(skb);
 	sgs = vsock->out_sgs;
 	sg_init_one(sgs[out_sg], virtio_vsock_hdr(skb),
 		    sizeof(*virtio_vsock_hdr(skb)));
@@ -164,13 +144,46 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	/* Usually this means that there is no more space available in
 	 * the vq
 	 */
+	if (ret < 0)
+		return ret;
+
+	virtio_transport_deliver_tap_pkt(skb);
+	return 0;
+}
+
+static void
+virtio_transport_send_pkt_work(struct work_struct *work)
+{
+	struct virtio_vsock *vsock =
+		container_of(work, struct virtio_vsock, send_pkt_work);
+	struct virtqueue *vq;
+	bool added = false;
+	bool restart_rx = false;
+
+	mutex_lock(&vsock->tx_lock);
+
+	if (!vsock->tx_run)
+		goto out;
+
+	vq = vsock->vqs[VSOCK_VQ_TX];
+
+	for (;;) {
+		struct sk_buff *skb;
+		bool reply;
+		int ret;
+
+		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
+		if (!skb)
+			break;
+
+		reply = virtio_vsock_skb_reply(skb);
+
+		ret = virtio_transport_send_skb(skb, vq, vsock);
 		if (ret < 0) {
 			virtio_vsock_skb_queue_head(&vsock->send_pkt_queue, skb);
 			break;
 		}
 
-		virtio_transport_deliver_tap_pkt(skb);
-
 		if (reply) {
 			struct virtqueue *rx_vq = vsock->vqs[VSOCK_VQ_RX];
 			int val;