netdev - Re: bpf filter : support for vlan tag

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Message-ID: <CAD6jFURcGt-xwE7WGXPvfGZ1JXAWC+sVNnN+gbpEyQSJYvxDnQ@mail.gmail.com>
Date:	Fri, 19 Oct 2012 22:53:20 +0200
From:	Daniel Borkmann <danborkmann@...earbox.net>
To:	Ani Sinha <ani@...stanetworks.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: bpf filter : support for vlan tag

On Fri, Oct 19, 2012 at 8:32 PM, Ani Sinha <ani@...stanetworks.com> wrote:
> how about this?
>
> On Tue, Oct 16, 2012 at 4:28 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>> @@ -341,6 +342,12 @@ load_b:
>>                 case BPF_S_ANC_CPU:
>>                         A = raw_smp_processor_id();
>>                         continue;
>> +               case BPF_S_ANC_VLAN_TAG:
>> +                       A = vlan_tx_tag_get(skb);
>> +                       continue;
>> +               case BPF_S_ANC_VLAN_TAG_PRESENT:
>> +                       A = !!vlan_tx_tag_present(skb);
>> +                       continue;
>>                 case BPF_S_ANC_NLATTR: {
>>                         struct nlattr *nla;
>
>
> +               case BPF_S_ANC_VLAN_TAG:
> +                       if (!vlan_tx_tag_present(skb)) {
> +                               return 0;
> +                       }
> +                       A = vlan_tx_tag_get(skb);
> +                       continue;

I didn't look into the code, but I assume that if no vlan is present,
then vlan_tx_tag_get might return 0 anyway. Also, your return is
simply wrong, since then after this instruction you leave the *whole*
BPF machine ignoring the rest of the filter program to process ...

> +               case BPF_S_ANC_VLAN_TAG_PRESENT :
> +                       A = !! vlan_tx_tag_present(skb);
> +                       continue;
>
> Now, is there any particular reason we are not using clan_get_tag() api?
>
> Thanks
> ani
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