[RFC PATCH v4 1/4] virtio/vsock: don't use skbuff state to account credit

[Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxx>]

'skb->len' can vary when we partially read the data, this complicates the
calculation of credit to be updated in 'virtio_transport_inc_rx_pkt()/
virtio_transport_dec_rx_pkt()'.

Also in 'virtio_transport_dec_rx_pkt()' we were miscalculating the
credit since 'skb->len' was redundant.

For these reasons, let's replace the use of skbuff state to calculate new
'rx_bytes'/'fwd_cnt' values with explicit value as input argument. This
makes code more simple, because it is not needed to change skbuff state
before each call to update 'rx_bytes'/'fwd_cnt'.

Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
---
 net/vmw_vsock/virtio_transport_common.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index a1581c77cf84..618680fd9906 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -241,21 +241,18 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 }
 
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
-					struct sk_buff *skb)
+					u32 len)
 {
-	if (vvs->rx_bytes + skb->len > vvs->buf_alloc)
+	if (vvs->rx_bytes + len > vvs->buf_alloc)
 		return false;
 
-	vvs->rx_bytes += skb->len;
+	vvs->rx_bytes += len;
 	return true;
 }
 
 static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
-					struct sk_buff *skb)
+					u32 len)
 {
-	int len;
-
-	len = skb_headroom(skb) - sizeof(struct virtio_vsock_hdr) - skb->len;
 	vvs->rx_bytes -= len;
 	vvs->fwd_cnt += len;
 }
@@ -388,7 +385,9 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 		skb_pull(skb, bytes);
 
 		if (skb->len == 0) {
-			virtio_transport_dec_rx_pkt(vvs, skb);
+			u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
+
+			virtio_transport_dec_rx_pkt(vvs, pkt_len);
 			consume_skb(skb);
 		} else {
 			__skb_queue_head(&vvs->rx_queue, skb);
@@ -437,17 +436,17 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 
 	while (!msg_ready) {
 		struct virtio_vsock_hdr *hdr;
+		size_t pkt_len;
 
 		skb = __skb_dequeue(&vvs->rx_queue);
 		if (!skb)
 			break;
 		hdr = virtio_vsock_hdr(skb);
+		pkt_len = (size_t)le32_to_cpu(hdr->len);
 
 		if (dequeued_len >= 0) {
-			size_t pkt_len;
 			size_t bytes_to_copy;
 
-			pkt_len = (size_t)le32_to_cpu(hdr->len);
 			bytes_to_copy = min(user_buf_len, pkt_len);
 
 			if (bytes_to_copy) {
@@ -484,7 +483,7 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 				msg->msg_flags |= MSG_EOR;
 		}
 
-		virtio_transport_dec_rx_pkt(vvs, skb);
+		virtio_transport_dec_rx_pkt(vvs, pkt_len);
 		kfree_skb(skb);
 	}
 
@@ -1040,7 +1039,7 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
 
 	spin_lock_bh(&vvs->rx_lock);
 
-	can_enqueue = virtio_transport_inc_rx_pkt(vvs, skb);
+	can_enqueue = virtio_transport_inc_rx_pkt(vvs, len);
 	if (!can_enqueue) {
 		free_pkt = true;
 		goto out;
-- 
2.25.1