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Message-ID: <94bd28f625f7ca066e8f2b2686c2493cfab386bd.camel@redhat.com>
Subject: Re: [PATCH net-next v2 2/3] vhost_net: Call peek_len when using xdp
From: Paolo Abeni <pabeni@redhat.com>
To: Yunjian Wang <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@huawei.com,  liwei395@huawei.com
Date: Thu, 29 Feb 2024 11:48:43 +0100
In-Reply-To: <1709118344-127812-1-git-send-email-wangyunjian@huawei.com>
References: <1709118344-127812-1-git-send-email-wangyunjian@huawei.com>
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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.
>=20
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> ---
>  drivers/vhost/net.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
>=20
> 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);
>  }
> =20
> +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 =3D &nvq->rxq;
> @@ -214,6 +219,13 @@ static int vhost_net_buf_peek(struct vhost_net_virtq=
ueue *nvq)
>  	if (!vhost_net_buf_is_empty(rxq))
>  		goto out;
> =20
> +	if (ptr_ring_empty(nvq->rx_ring)) {
> +		struct socket *sock =3D 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.

Cheers,

Paolo