[RFC bpf-next 2/5] veth: Support rx timestamp metadata for xdp

[Stanislav Fomichev <sdf@google.com>]

xskxceiver conveniently setups up veth pairs so it seems logical
to use veth as an example for some of the metadata handling.

We timestamp skb right when we "receive" it, store its
pointer in xdp_buff->priv and generate BPF bytecode to
reach it from the BPF program.

This largely follows the idea of "store some queue context in
the xdp_buff/xdp_frame so the metadata can be reached out
from the BPF program".

Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 drivers/net/veth.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 09682ea3354e..35396dd73de0 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -597,6 +597,7 @@ static struct xdp_frame *veth_xdp_rcv_one(struct veth_rq *rq,
 
 		xdp_convert_frame_to_buff(frame, &xdp);
 		xdp.rxq = &rq->xdp_rxq;
+		xdp.priv = NULL;
 
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 
@@ -820,6 +821,7 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
 
 	orig_data = xdp.data;
 	orig_data_end = xdp.data_end;
+	xdp.priv = skb;
 
 	act = bpf_prog_run_xdp(xdp_prog, &xdp);
 
@@ -936,6 +938,7 @@ static int veth_xdp_rcv(struct veth_rq *rq, int budget,
 			struct sk_buff *skb = ptr;
 
 			stats->xdp_bytes += skb->len;
+			__net_timestamp(skb);
 			skb = veth_xdp_rcv_skb(rq, skb, bq, stats);
 			if (skb) {
 				if (skb_shared(skb) || skb_unclone(skb, GFP_ATOMIC))
@@ -1595,6 +1598,33 @@ static int veth_xdp(struct net_device *dev, struct netdev_bpf *xdp)
 	}
 }
 
+static int veth_unroll_kfunc(struct bpf_prog *prog, struct bpf_insn *insn)
+{
+	u32 func_id = insn->imm;
+
+	if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_HAVE_RX_TIMESTAMP)) {
+		/* return true; */
+		insn[0] = BPF_MOV64_IMM(BPF_REG_0, 1);
+		return 1;
+	} else if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP)) {
+		/* r1 = ((struct xdp_buff *)r1)->priv; [skb] */
+		insn[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1,
+				      offsetof(struct xdp_buff, priv));
+		/* if (r1 == NULL) { */
+		insn[1] = BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 1);
+		/*	return 0; */
+		insn[2] = BPF_MOV64_IMM(BPF_REG_0, 0);
+		/* } else { */
+		/*	return ((struct sk_buff *)r1)->tstamp; */
+		insn[3] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
+				      offsetof(struct sk_buff, tstamp));
+		/* } */
+		return 4;
+	}
+
+	return 0;
+}
+
 static const struct net_device_ops veth_netdev_ops = {
 	.ndo_init            = veth_dev_init,
 	.ndo_open            = veth_open,
@@ -1614,6 +1644,7 @@ static const struct net_device_ops veth_netdev_ops = {
 	.ndo_bpf		= veth_xdp,
 	.ndo_xdp_xmit		= veth_ndo_xdp_xmit,
 	.ndo_get_peer_dev	= veth_peer_dev,
+	.ndo_unroll_kfunc       = veth_unroll_kfunc,
 };
 
 #define VETH_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HW_CSUM | \
-- 
2.38.1.273.g43a17bfeac-goog