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

[Jesper Dangaard Brouer <brouer@redhat.com>]

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 <brouer@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 */