[PATCH bpf-next RFCv3 5/6] veth: add AF_XDP RX support.

[William Tu <u9012063@gmail.com>]

If the receiving veth side has umem rx enabled, the patch
directly copy the packet from the peer side's send buffer
to the umem receive buffer.  This requires running AF_XDP
as both side of the veth peer.  For example:
Receiver:
  # ip netns exec at_ns0 xdpsock -r -N -z -i p0
Sender:
  # xdpsock -i p1 -t -N -z
The performance increases from 1.4Mpps to 2.3Mpps.

Signed-off-by: William Tu <u9012063@gmail.com>
---
 drivers/net/veth.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 551444195398..8aac67554880 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -766,11 +766,28 @@ static int veth_xsk_poll(struct napi_struct *napi, int budget)
 		struct sk_buff *skb;
 		struct page *page;
 		void *vaddr;
+		u64 handle;
 		u32 len;
 
 		if (!xsk_umem_consume_tx_virtual(peer_rq->xsk_umem, &vaddr, &len))
 			break;
 
+		if (rq->xsk_umem && xsk_umem_peek_addr(rq->xsk_umem, &handle)) {
+			char *daddr;
+			u64 hr = 0;
+
+			/* the peer side also has umem enabled,
+			 * copy directly to it.
+			 */
+			handle &= rq->xsk_umem->chunk_mask;
+			hr = rq->xsk_umem->headroom + XDP_PACKET_HEADROOM;
+			daddr = xdp_umem_get_data(rq->xsk_umem, handle);
+			daddr += hr;
+			memcpy((void *)daddr, vaddr, len);
+			xsk_umem_discard_addr(rq->xsk_umem);
+			vaddr = daddr;
+		}
+
 		xdpf.data = vaddr + metasize;
 		xdpf.len = len;
 		xdpf.headroom = 0;
-- 
2.7.4