netdev - Re: [Patch net-next] ipv6: separate out procfs code from mcast.c

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Message-ID: <87d2tlv32i.fsf@nemi.mork.no>
Date:	Tue, 23 Apr 2013 14:33:57 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Cong Wang <amwang@...hat.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	yoshfuji@...ux-ipv6.org
Subject: Re: [Patch net-next] ipv6: separate out procfs code from mcast.c

Cong Wang <amwang@...hat.com> writes:

> On Tue, 2013-04-23 at 03:36 -0400, David Miller wrote:
>> From: Cong Wang <amwang@...hat.com>
>> Date: Tue, 23 Apr 2013 15:30:20 +0800
>> 
>> > This is hard to do, as in the email I replied to Stephen. So I
>> > prefer to just add a Kconfig dependency, at least for now.
>> 
>> A Kconfig hack is exactly what I've told you is an unacceptable
>> solution.
>
> Please enlighten me for a third solution. :)

This is an completely untested idea....

I note that vxlan_init_net requires a successful sock_create_kern().
That implies a request_module("net-pf-...") followed by try_module_get.

So if the sock_create_kern(PF_INET6, ..) succeeds then you *know* you
have IPv6. If it fails with -EAFNOSUPPORT, then you could fall back to
sock_create_kern(PF_INET, ..) and set a flag indicating that runtime
IPv6 support is disabled.  Then use this flag to allow/deny configuring
any IPv6 destinations.

You may also have to protect the IPv6 modular symbols you use with
symbol_request() or similar to prevent vxlan from depending on IPv6.  I
dunno...

If nothing else, I believe this is a crazy enough hack that David may
want to reconsider one of your other two solutions :)

Bjørn
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