Re: [PATCH v2 3/8] vsock/virtio: Move length check to callers of virtio_vsock_skb_rx_put()

[Stefano Garzarella]

On Tue, Jul 01, 2025 at 05:45:02PM +0100, Will Deacon wrote:
> virtio_vsock_skb_rx_put() only calls skb_put() if the length in the
> packet header is not zero even though skb_put() handles this case
> gracefully.
>
> Remove the functionally redundant check from virtio_vsock_skb_rx_put()
> and, on the assumption that this is a worthwhile optimisation for
> handling credit messages, augment the existing length checks in
> virtio_transport_rx_work() to elide the call for zero-length payloads.
> Note that the vhost code already has similar logic in
> vhost_vsock_alloc_skb().
>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> ---
> include/linux/virtio_vsock.h     | 4 +---
> net/vmw_vsock/virtio_transport.c | 4 +++-
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 36fb3edfa403..eb6980aa19fd 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -52,9 +52,7 @@ static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
> 	u32 len;
>
> 	len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
> -
> -	if (len > 0)
> -		skb_put(skb, len);
> +	skb_put(skb, len);

Since the caller is supposed to check the len, can we just pass it as 
parameter?

So we can avoid the `le32_to_cpu(virtio_vsock_hdr(skb)->len)` here.

Thanks,
Stefano

> }
>
> static inline struct sk_buff *virtio_vsock_alloc_skb(unsigned int size, gfp_t mask)
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index bd2c6aaa1a93..488e6ddc6ffa 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -656,7 +656,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 				continue;
> 			}
>
> -			virtio_vsock_skb_rx_put(skb);
> +			if (payload_len)
> +				virtio_vsock_skb_rx_put(skb);
> +
> 			virtio_transport_deliver_tap_pkt(skb);
> 			virtio_transport_recv_pkt(&virtio_transport, skb);
> 		}
> --
> 2.50.0.727.gbf7dc18ff4-goog