Re: [PATCH bpf-next 04/10] [bpf]: make generic xdp compatible w/ bpf_xdp_adjust_tail

[Alexei Starovoitov]

On Mon, Apr 16, 2018 at 11:51:25PM -0700, Nikita V. Shirokov wrote:
> w/ bpf_xdp_adjust_tail helper xdp's data_end pointer could be changed as
> well (only "decrease" of pointer's location is going to be supported).
> changing of this pointer will change packet's size.
> for generic XDP we need to reflect this packet's length change by
> adjusting skb's tail pointer
> 
> Signed-off-by: Nikita V. Shirokov 

Acked-by: Alexei Starovoitov 

pls also change the order of the test/sample patches.
they should come last, since they will work only after this one
and all other driver support.

[PATCH bpf-next 04/10] [bpf]: make generic xdp compatible w/ bpf_xdp_adjust_tail

[Nikita V. Shirokov]

w/ bpf_xdp_adjust_tail helper xdp's data_end pointer could be changed as
well (only "decrease" of pointer's location is going to be supported).
changing of this pointer will change packet's size.
for generic XDP we need to reflect this packet's length change by
adjusting skb's tail pointer

Signed-off-by: Nikita V. Shirokov 
---
 net/core/dev.c | 10 +-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 969462ebb296..11c789231a03 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3996,9 +3996,9 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 struct bpf_prog *xdp_prog)
 {
struct netdev_rx_queue *rxqueue;
+   void *orig_data, *orig_data_end;
u32 metalen, act = XDP_DROP;
struct xdp_buff xdp;
-   void *orig_data;
int hlen, off;
u32 mac_len;
 
@@ -4037,6 +4037,7 @@ 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);
+   orig_data_end = xdp.data_end;
orig_data = xdp.data;
 
rxqueue = netif_get_rxqueue(skb);
@@ -4051,6 +4052,13 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
__skb_push(skb, -off);
skb->mac_header += off;
 
+   /* check if bpf_xdp_adjust_tail was used. it can only "shrink"
+* pckt.
+*/
+   off = orig_data_end - xdp.data_end;
+   if (off != 0)
+   skb_set_tail_pointer(skb, xdp.data_end - xdp.data);
+
switch (act) {
case XDP_REDIRECT:
case XDP_TX:
-- 
2.15.1