[bpf-next V3 PATCH 07/15] virtio_net: convert to use generic xdp_frame and xdp_return_frame API

[Jesper Dangaard Brouer]

The virtio_net driver assumes XDP frames are always released based on
page refcnt (via put_page).  Thus, is only queues the XDP data pointer
address and uses virt_to_head_page() to retrieve struct page.

Use the XDP return API to get away from such assumptions. Instead
queue an xdp_frame, which allow us to use the xdp_return_frame API,
when releasing the frame.

Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
---
 drivers/net/virtio_net.c |   31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 23374603e4d9..6c4220450506 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -419,30 +419,41 @@ static bool __virtnet_xdp_xmit(struct virtnet_info *vi,
                               struct xdp_buff *xdp)
 {
        struct virtio_net_hdr_mrg_rxbuf *hdr;
-       unsigned int len;
+       struct xdp_frame *xdpf, *xdpf_sent;
        struct send_queue *sq;
+       unsigned int len;
        unsigned int qp;
-       void *xdp_sent;
        int err;
 
        qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
        sq = &vi->sq[qp];
 
        /* Free up any pending old buffers before queueing new ones. */
-       while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) {
-               struct page *sent_page = virt_to_head_page(xdp_sent);
+       while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
+               xdp_return_frame(xdpf_sent->data, &xdpf_sent->mem);
 
-               put_page(sent_page);
-       }
+       xdpf = convert_to_xdp_frame(xdp);
+       if (unlikely(!xdpf))
+               return -EOVERFLOW;
+
+       /* virtqueue want to use data area in-front of packet */
+       if (unlikely(xdpf->metasize > 0))
+               return -EOPNOTSUPP;
+
+       if (unlikely(xdpf->headroom < vi->hdr_len))
+               return -EOVERFLOW;
 
-       xdp->data -= vi->hdr_len;
+       /* Make room for virtqueue hdr (also change xdpf->headroom?) */
+       xdpf->data -= vi->hdr_len;
        /* Zero header and leave csum up to XDP layers */
-       hdr = xdp->data;
+       hdr = xdpf->data;
        memset(hdr, 0, vi->hdr_len);
+       hdr->hdr.hdr_len = xdpf->len; /* Q: is this needed? */
+       xdpf->len   += vi->hdr_len;
 
-       sg_init_one(sq->sg, xdp->data, xdp->data_end - xdp->data);
+       sg_init_one(sq->sg, xdpf->data, xdpf->len);
 
-       err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp->data, GFP_ATOMIC);
+       err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdpf, GFP_ATOMIC);
        if (unlikely(err))
                return false; /* Caller handle free/refcnt */