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

[Will Deacon <will@kernel.org>]

On Wed, Jul 02, 2025 at 06:28:37PM +0200, Stefano Garzarella wrote:
> 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@kernel.org>
> > ---
> > 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.

Sure, I'll do that. It means that virtio_vsock_skb_rx_put() will briefly
be a simple wrapper around skb_put() but once the non-linear handling
comes in then it becomes useful again.

Will