Re: [PATCH v3 net-next RFC] Generic XDP

[David Miller]

From: David Ahern <d...@cumulusnetworks.com>
Date: Wed, 12 Apr 2017 13:54:20 -0600

> packet passed to xdp seems to be messed up

Ok, the problem is that skb->mac_len isn't set properly at this point.
That doesn't happen until __netif_receive_skb_core().

I'm also not setting xdp.data_hard_start properly.

It should work better with this small diff:

diff --git a/net/core/dev.c b/net/core/dev.c
index 9ed4569..d36ae8f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4289,6 +4289,7 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
        u32 act = XDP_DROP;
        void *orig_data;
        int hlen, off;
+       u32 mac_len;
 
        if (skb_linearize(skb))
                goto do_drop;
@@ -4296,10 +4297,11 @@ static u32 netif_receive_generic_xdp(struct sk_buff 
*skb,
        /* The XDP program wants to see the packet starting at the MAC
         * header.
         */
-       hlen = skb_headlen(skb) + skb->mac_len;
-       xdp.data = skb->data - skb->mac_len;
+       mac_len = skb->data - skb_mac_header(skb);
+       hlen = skb_headlen(skb) + mac_len;
+       xdp.data = skb->data - mac_len;
        xdp.data_end = xdp.data + hlen;
-       xdp.data_hard_start = xdp.data - skb_headroom(skb);
+       xdp.data_hard_start = skb->data - skb_headroom(skb);
        orig_data = xdp.data;
 
        act = bpf_prog_run_xdp(xdp_prog, &xdp);