[PATCH net-next RFC v1 4/4] veth: when XDP is loaded increase needed_headroom

[Jesper Dangaard Brouer <hawk@kernel.org>]

When sending (sendmsg) SKBs out an veth device, the SKB headroom is too small
to satisfy XDP on the receiving veth peer device.

For AF_XDP (normal non-zero-copy) it is worth noticing that xsk_build_skb()
adjust headroom according to dev->needed_headroom. Other parts of the kernel
also take this into account (see macro LL_RESERVED_SPACE).

This solves the XDP_PACKET_HEADROOM check in veth_convert_skb_to_xdp_buff().

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
---
 drivers/net/veth.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 8e117cc44fda..3630e9124071 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1649,6 +1649,7 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		if (!old_prog) {
 			peer->hw_features &= ~NETIF_F_GSO_SOFTWARE;
 			peer->max_mtu = max_mtu;
+			veth_set_rx_headroom(dev, XDP_PACKET_HEADROOM);
 		}
 
 		xdp_features_set_redirect_target(peer, true);
@@ -1666,6 +1667,7 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 				peer->hw_features |= NETIF_F_GSO_SOFTWARE;
 				peer->max_mtu = ETH_MAX_MTU;
 			}
+			veth_set_rx_headroom(dev, -1);
 		}
 		bpf_prog_put(old_prog);
 	}