On 16-12-02 12:51 PM, John Fastabend wrote:
> This adds support for the XDP_TX action to virtio_net. When an XDP
> program is run and returns the XDP_TX action the virtio_net XDP
> implementation will transmit the packet on a TX queue that aligns
> with the current CPU that the XDP packet was processed on.
>
> Before sending the packet the header is zeroed. Also XDP is expected
> to handle checksum correctly so no checksum offload support is
> provided.
>
> Signed-off-by: John Fastabend <john.r.fastab...@intel.com>
> ---
> drivers/net/virtio_net.c | 63
> ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 60 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b67203e..137caba 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -330,12 +330,43 @@ static struct sk_buff *page_to_skb(struct virtnet_info
> *vi,
> return skb;
> }
>
> +static void virtnet_xdp_xmit(struct virtnet_info *vi,
> + unsigned int qnum, struct xdp_buff *xdp)
> +{
> + struct send_queue *sq = &vi->sq[qnum];
> + struct virtio_net_hdr_mrg_rxbuf *hdr;
> + unsigned int num_sg, len;
> + void *xdp_sent;
> + int err;
> +
> + /* Free up any pending old buffers before queueing new ones. */
> + while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> + struct page *page = virt_to_head_page(xdp_sent);
> +
> + put_page(page);
> + }
> +
> + /* Zero header and leave csum up to XDP layers */
> + hdr = xdp->data;
> + memset(hdr, 0, vi->hdr_len);
> +
> + num_sg = 1;
> + sg_init_one(sq->sg, xdp->data, xdp->data_end - xdp->data);
> + err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
> + xdp->data, GFP_ATOMIC);
> + if (unlikely(err))
> + put_page(virt_to_head_page(xdp->data));
> + else
> + virtqueue_kick(sq->vq);
> +}
> +
Hi Michael,
Any idea why the above pattern
> + err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
> + xdp->data, GFP_ATOMIC);
> + if (unlikely(err))
> + put_page(virt_to_head_page(xdp->data));
> + else
> + virtqueue_kick(sq->vq);
> +}
would cause a hang but if I call the virtqueue_kick as below
even in the error case everything seems to be fine.
err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
xdp->data, GFP_ATOMIC);
if (unlikely(err))
put_page(virt_to_head_page(xdp->data));
virtqueue_kick(sq->vq);
I'll take a look through the virtio code but thought I might ask in
case you know off-hand or it could be something else entirely.
I noticed virtio_input.c uses the second pattern and virtio_net.c
uses the above pattern but I'm guessing it never gets exercised due
to stack backoff.
Thanks,
John
