[RFC PATCH bpf-next v1 6/7] veth: support the rx_csum XDP metadata hint

[Vladimir Vdovin <deliran@verdict.gg>]

Implement xmo_rx_csum from skb->ip_summed.  veth has no real hardware;
this surfaces whatever checksum verdict the skb already carries and makes
the metadata kfunc testable without a NIC.

Signed-off-by: Vladimir Vdovin <deliran@verdict.gg>
---
 drivers/net/veth.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 1c5142149175..b7bc5a3b07e5 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1700,6 +1700,28 @@ static int veth_xdp_rx_vlan_tag(const struct xdp_md *ctx, __be16 *vlan_proto,
 	return err;
 }
 
+static int veth_xdp_rx_csum(const struct xdp_md *ctx,
+			    enum xdp_csum_status *csum_status)
+{
+	const struct veth_xdp_buff *_ctx = (void *)ctx;
+	const struct sk_buff *skb = _ctx->skb;
+
+	if (!skb)
+		return -ENODATA;
+
+	/* veth has no real hardware; surface whatever checksum verdict the
+	 * skb already carries (e.g. CHECKSUM_PARTIAL/UNNECESSARY from a local
+	 * sender or a previous validation).
+	 */
+	if (skb->ip_summed == CHECKSUM_UNNECESSARY ||
+	    skb->ip_summed == CHECKSUM_PARTIAL)
+		*csum_status = XDP_CSUM_VERIFIED;
+	else
+		*csum_status = XDP_CSUM_NONE;
+
+	return 0;
+}
+
 static const struct net_device_ops veth_netdev_ops = {
 	.ndo_init            = veth_dev_init,
 	.ndo_open            = veth_open,
@@ -1725,6 +1747,7 @@ static const struct xdp_metadata_ops veth_xdp_metadata_ops = {
 	.xmo_rx_timestamp		= veth_xdp_rx_timestamp,
 	.xmo_rx_hash			= veth_xdp_rx_hash,
 	.xmo_rx_vlan_tag		= veth_xdp_rx_vlan_tag,
+	.xmo_rx_csum			= veth_xdp_rx_csum,
 };
 
 #define VETH_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HW_CSUM | \
-- 
2.47.0