netdev - Re: __sk_buff.data

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Date:   Thu, 20 Apr 2017 00:20:59 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: __sk_buff.data_end

On Wed, 2017-04-19 at 23:31 +0200, Johannes Berg wrote:
> Hi Alexei, Daniel,
> 
> I'm looking at adding the __wifi_sk_buff I talked about, and I notice
> that it uses CB space to store data_end. Unfortunately, in a lot of
> cases, we don't have any CB space to spare in wifi.

I guess I can work around this, would this seem reasonable?

 struct bpf_skb_data_end {
        struct qdisc_skb_cb qdisc_cb;
-       void *data_end;
+       /*
+        * The alignment here is for mac80211, since that doesn't use
+        * a pointer but a u64 value and needs to save/restore that
+        * across running its BPF programs.
+        */
+       void *data_end __aligned(sizeof(u64));
 };

johannes