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 11:24:35 -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

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.

So no I am not talking about anything that is driver specific.  I am
talking about reasonable userspace expectations.  Because otherwise
we simply loose the information that a packet was vlan tagged, and
in doing so we break existing userspace applications because of our
bugs.



Eric



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