Re: [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2020-05-06 07:53:42
Also in:
bpf, lkml, virtualization
On Wed, May 06, 2020 at 02:16:32PM +0800, Jason Wang wrote:
We tried to reserve space for vnet header before xdp.data_hard_start. But this is useless since the packet could be modified by XDP which may invalidate the information stored in the header and there's no way for XDP to know the existence of the vnet header currently.
What do you mean? Doesn't XDP_PASS use the header in the buffer?
So let's just not reserve space for vnet header in this case.
In any case, we can find out XDP does head adjustments if we need to.
quoted hunk ↗ jump to hunk
Cc: Jesper Dangaard Brouer <redacted> Signed-off-by: Jason Wang <jasowang@redhat.com> --- drivers/net/virtio_net.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 11f722460513..98dd75b665a5 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c@@ -684,8 +684,8 @@ static struct sk_buff *receive_small(struct net_device *dev, page = xdp_page; } - xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len; - xdp.data = xdp.data_hard_start + xdp_headroom; + xdp.data_hard_start = buf + VIRTNET_RX_PAD; + xdp.data = xdp.data_hard_start + xdp_headroom + vi->hdr_len; xdp.data_end = xdp.data + len; xdp.data_meta = xdp.data; xdp.rxq = &rq->xdp_rxq;@@ -845,7 +845,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, * the descriptor on if we get an XDP_TX return code. */ data = page_address(xdp_page) + offset; - xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len; + xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM; xdp.data = data + vi->hdr_len; xdp.data_end = xdp.data + (len - vi->hdr_len); xdp.data_meta = xdp.data;-- 2.20.1