RE: [PATCH net-next v2 2/3] vhost_net: Call peek_len when using xdp

[wangyunjian <wangyunjian@huawei.com>]

> -----Original Message-----
> From: Paolo Abeni [mailto:pabeni@redhat.com]
> Sent: Thursday, February 29, 2024 6:49 PM
> To: wangyunjian <wangyunjian@huawei.com>; mst@redhat.com;
> willemdebruijn.kernel@gmail.com; jasowang@redhat.com; kuba@kernel.org;
> bjorn@kernel.org; magnus.karlsson@intel.com; maciej.fijalkowski@intel.com;
> jonathan.lemon@gmail.com; davem@davemloft.net
> Cc: bpf@vger.kernel.org; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; kvm@vger.kernel.org;
> virtualization@lists.linux.dev; xudingke <xudingke@huawei.com>; liwei (DT)
> <liwei395@huawei.com>
> Subject: Re: [PATCH net-next v2 2/3] vhost_net: Call peek_len when using xdp
> 
> On Wed, 2024-02-28 at 19:05 +0800, Yunjian Wang wrote:
> > If TUN supports AF_XDP TX zero-copy, the XDP program will enqueue
> > packets to the XDP ring and wake up the vhost worker. This requires
> > the vhost worker to call peek_len(), which can be used to consume XDP
> > descriptors.
> >
> > Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> > ---
> >  drivers/vhost/net.c | 17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index
> > f2ed7167c848..077e74421558 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -207,6 +207,11 @@ static int vhost_net_buf_peek_len(void *ptr)
> >  	return __skb_array_len_with_tag(ptr);  }
> >
> > +static bool vhost_sock_xdp(struct socket *sock) {
> > +	return sock_flag(sock->sk, SOCK_XDP); }
> > +
> >  static int vhost_net_buf_peek(struct vhost_net_virtqueue *nvq)  {
> >  	struct vhost_net_buf *rxq = &nvq->rxq; @@ -214,6 +219,13 @@ static
> > int vhost_net_buf_peek(struct vhost_net_virtqueue *nvq)
> >  	if (!vhost_net_buf_is_empty(rxq))
> >  		goto out;
> >
> > +	if (ptr_ring_empty(nvq->rx_ring)) {
> > +		struct socket *sock = vhost_vq_get_backend(&nvq->vq);
> > +		/* Call peek_len to consume XSK descriptors, when using xdp */
> > +		if (vhost_sock_xdp(sock) && sock->ops->peek_len)
> > +			sock->ops->peek_len(sock);
> 
> This really looks like a socket API misuse. Why can't you use ptr-ring primitives
> to consume XSK descriptors? peek_len could be constified some day, this code
> will prevent such (good) thing.

Thank you for your suggestion. I will consider that with Patch 3/3.

> 
> Cheers,
> 
> Paolo