netdev - Re: [patch net-next-2.6 v2] net: vlan: make non-hw-accel rx path similar to hw-accel

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Date:	Sun, 22 May 2011 12:33:36 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jesse Gross <jesse@...ira.com>
Cc:	Jiri Pirko <jpirko@...hat.com>,
	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>, Changli Gao <xiaosuo@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	shemminger@...ux-foundation.org, kaber@...sh.net, fubar@...ibm.com,
	eric.dumazet@...il.com, andy@...yhouse.net
Subject: Re: [patch net-next-2.6 v2] net: vlan: make non-hw-accel rx path similar to hw-accel

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Jesse Gross <jesse@...ira.com> writes:
>
>> On Sat, May 21, 2011 at 11:34 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>> Jiri Pirko <jpirko@...hat.com> writes:
>>>
>>>> Sun, May 22, 2011 at 04:59:49AM CEST, nicolas.2p.debian@...il.com wrote:
>>>>
>>>> <snip>
>>>>>
>>>>>And because some setups may still require the skb not to be untagged,
>>>>>may be we need the ability to re-tag the skb in some situations...
>>>>>When a protocol handler or rx_handler is explicitly registered on a
>>>>>net_device which expect to receive tagged skb, we should deliver
>>>>>tagged skb to it... Arguably, this may sound incredible for the
>>>>>general case, but may be required for not-so-special cases like
>>>>>bridge or protocol analyzer.
>>>>
>>>> Wait, what setups/code require the skb not to be untagged? If there's
>>>> such, it should be fixed.
>>>
>>> tcpdump on the non-vlan interface for one.
>>
>> There are some drivers still using the old vlan model that will drop
>> tags or packets when no vlan group is configured but that's a driver
>> problem, not one with networking core or tcpdump.
>
> On receive if we have stripped the vlan header and then we go to deliver
> the interrupt to a pf_packet socket (on a non-vlan interface) before
> or as part of the deliver of the packet to user space we need to
> re-add the vlan header.  Additionally the socket filter on a pf_packet
> socket needs to behave as though we have a vlan header.

Hmm.  Taking a second look the pf_packet code and with hardware vlan
header removal isn't completely broken.  It is possible to receive
packet auxdata and get the information from the vlan header.

It stills seems like a pretty messed up interface to me.  Especially
since the socket filter can't get at the information in the stripped
vlan header, but that is another matter entirely.

Eric
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