net: XDP-generic determining XDP frame size (a075767b) · Commits · 戴 / test

The SKB "head" pointer points to the data area that contains skb_shared_info, that can be found via skb_end_pointer(). Given xdp->data_hard_start have been established (basically pointing to skb->head), frame size is between skb_end_pointer() and data_hard_start, plus the size reserved to skb_shared_info. Change the bpf_xdp_adjust_tail offset adjust of skb->len, to be a positive offset number on grow, and negative number on shrink. As this seems more natural when reading the code. Signed-off-by:

Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Toke Høiland-Jørgensen <toke@redhat.com> Link: https://lore.kernel.org/bpf/158945336804.97035.7164852191163722056.stgit@firesoul

net/core/dev.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -4617,6 +4617,11 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
		xdp->data_meta = xdp->data;
		xdp->data_end = xdp->data + hlen;
		xdp->data_hard_start = skb->data - skb_headroom(skb);

		/* 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_end = xdp->data_end;
		orig_data = xdp->data;
		eth = (struct ethhdr *)xdp->data;
		@@ -4640,14 +4645,11 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
		skb_reset_network_header(skb);
		}

		/* check if bpf_xdp_adjust_tail was used. it can only "shrink"
		* pckt.
		*/
		off = orig_data_end - xdp->data_end;
		/* check if bpf_xdp_adjust_tail was used */
		off = xdp->data_end - orig_data_end;
		if (off != 0) {
		skb_set_tail_pointer(skb, xdp->data_end - xdp->data);
		skb->len -= off;

		skb->len += off; /* positive on grow, negative on shrink */
		}

		/* check if XDP changed eth hdr such SKB needs update */

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