[PATCH RFC v1 14/15] veth: xdp using frame_sz in veth driver

@@ -492,6 +492,8 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
 					unsigned int *xdp_xmit,
 					struct veth_xdp_tx_bq *bq)
 {
+// hmm... do we really need to exclude sizeof(struct xdp_frame) ?
+// ... as bpf_xdp_adjust_head() already handle this.
 	void *hard_start = frame->data - frame->headroom;
 	void *head = hard_start - sizeof(struct xdp_frame);
 	int len = frame->len, delta = 0;

@@ -506,11 +508,12 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
 		struct xdp_buff xdp;
 		u32 act;
 
-		xdp.data_hard_start = hard_start;
+		xdp.data_hard_start = hard_start; /* exclude xdp_frame area */
 		xdp.data = frame->data;
 		xdp.data_end = frame->data + frame->len;
 		xdp.data_meta = frame->data - frame->metasize;
 		xdp.rxq = &rq->xdp_rxq;
+		xdp.frame_sz = frame->frame_sz - sizeof(struct xdp_frame);
 
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 

@@ -639,6 +642,11 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq, struct sk_buff *skb,
 	xdp.data_end = xdp.data + pktlen;
 	xdp.data_meta = xdp.data;
 	xdp.rxq = &rq->xdp_rxq;
+
+	/* SKB "head" area always have tailroom for skb_shared_info */
+	xdp.frame_sz = (void *)skb_end_pointer(skb) - xdp.data_hard_start;
+	xdp.frame_sz += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
 	orig_data = xdp.data;
 	orig_data_end = xdp.data_end;
 

@@ -678,6 +686,7 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq, struct sk_buff *skb,
 	}
 	rcu_read_unlock();
 
+	/* check if bpf_xdp_adjust_head was used */
 	delta = orig_data - xdp.data;
 	off = mac_len + delta;
 	if (off > 0)

@@ -685,9 +694,11 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq, struct sk_buff *skb,
 	else if (off < 0)
 		__skb_pull(skb, -off);
 	skb->mac_header -= delta;
+
+	/* check if bpf_xdp_adjust_tail was used */
 	off = xdp.data_end - orig_data_end;
 	if (off != 0)
-		__skb_put(skb, off);
+		__skb_put(skb, off); /* positive on grow, negative on shrink */
 	skb->protocol = eth_type_trans(skb, rq->dev);
 
 	metalen = xdp.data - xdp.data_meta;