netdev - Re: [PATCH] openvswitch: Make IPv6 packet parsing dependent on IPv6 config

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Date:	Fri, 16 Nov 2012 12:43:32 -0500
From:	Vlad Yasevich <vyasevic@...hat.com>
To:	Jesse Gross <jesse@...ira.com>
CC:	dev@...nvswitch.org, netdev@...r.kernel.org, davem@...emloft.net,
	fengguang.wu@...el.com
Subject: Re: [PATCH] openvswitch: Make IPv6 packet parsing dependent on IPv6
 config

On 11/16/2012 12:26 PM, Jesse Gross wrote:
> On Fri, Nov 16, 2012 at 7:40 AM, Vlad Yasevich <vyasevic@...hat.com> wrote:
>
>> Openvswitch attempts to use IPv6 packet parsing functions without
>> any dependency on IPv6 (unlike every other place in kernel).  Pull
>> the IPv6 code in openvswitch togeter and put a conditional that's
>> dependent on CONFIG_IPV6.
>>
>> Resolves:
>> net/built-in.o: In function `ovs_flow_extract':
>> (.text+0xbf5d5): undefined reference to `ipv6_skip_exthdr'
>>
>> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
>
>
> Doesn't this move in the opposite direction of your patches to make IPv6
> GSO/GRO always available?  The packets being processed here
> are generally created by the guest but with Open vSwitch running on the
> host.  Also, ipv6_skip_exthdr() is in exthdrs_core.c, so it actually is
> always available.  I suspect that the real problem is that the dependency
> on the ipv6 directory changed to CONFIG_INET and Open vSwitch should now
> depend on this.
>

Yes and no... :)  IPv6 uses a bunch of IPv4 code all over.  IPv4 is 
enabled with CONFIG_INET and IPv6 with CONFIG_NET.  So creates a strange 
imbalance.  By shifting IPv6 to CONFIG_INET (which is where it
lives and what enables its selection during config process), we now have 
a dependency with openvswitch.

All other users of ipv6_skip_exthdr have it either under the IS_ENABLED 
conditional or through some other means that don't build it when INET is
completely turned off.  This patch does the same for openvswitch.

I see 2 alternatives to this:
  1) Make openvswitch depend on CONFIG_INET.
  2) Pull a ton of code out of CONFIG_INET (v4 and v6) and into 
CONFIG_NET.  This could start with IPv6 header parsing and maybe even
include GSO/TSO (but not sure how much sense that would be).

What's your take?

-vlad
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