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net: XDP-generic determining XDP frame size

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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
This commit is contained in:
Jesper Dangaard Brouer 2020-05-14 12:49:28 +02:00 committed by Alexei Starovoitov
parent 495de55f70
commit a075767bbd
1 changed files with 8 additions and 6 deletions
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14
net/core/dev.c
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@ -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 */