[PATCH RFC v1 10/15] net: XDP-generic determining XDP frame size
From: Jesper Dangaard Brouer <hidden>
Date: 2020-03-17 17:30:24
Also in:
bpf
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 fix up 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 <redacted> --- net/core/dev.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 9c941cd38b13..645e5c48a52f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -4546,6 +4546,11 @@ 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;
@@ -4569,14 +4574,11 @@ 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 */