netdev - Re: [PATCH v2 net-next] net: filter: export pkt_type

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Date:	Thu, 4 Sep 2014 13:51:18 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Laight <David.Laight@...lab.com>,
	Denis Kirjanov <kirjanov@...il.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Denis Kirjanov <kda@...ux-powerpc.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Markos Chandras <markos.chandras@...tec.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH v2 net-next] net: filter: export pkt_type_offset() helper

On Thu, Sep 4, 2014 at 7:41 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> On Do, 2014-09-04 at 07:35 -0700, Eric Dumazet wrote:
>> On Thu, 2014-09-04 at 16:33 +0200, Hannes Frederic Sowa wrote:
>>
>> > Which btw. also uses int, which might change alignment of structures.
>>
>> You missed the point .
>>
>> kmemcheck wants to make sure the whole word is set, or else you could
>> get false positives.
>>
>> kmemcheck needs are quite different.
>
> Now that you said it, I understand. :)
>
> You were right with the int vs. u8 thing all along. gcc aligns the
> datatype on the next struct field and not on the whole field, as I
> expected. So excuse my error above.
>
> I think the latest proposals looks good?

to me: yes
and I think your latest half-patch with:
+       __u8                    __pkt_type_offset[0];
also looks good.

Are you going to take it over from Denis here?

while at it would you fix sparc jit as well that has comment:
#if 0
                                /* GCC won't let us take the address of
                                 * a bit field even though we very much
                                 * know what we are doing here.
                                 */
                        case BPF_ANC | SKF_AD_PKTTYPE:
                                __emit_skb_load8(pkt_type, r_A);
                                emit_alu_K(SRL, 5);
                                break;
#endif
should be able to replace 'pkt_type' above with __pkt_type_offset...
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