netdev - Re: switching network namespace midway

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Date:	Thu, 25 Oct 2012 11:29:34 -0400
From:	rsa <ravi.mlists@...il.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>, netdev@...r.kernel.org
Subject: Re: switching network namespace midway

Hi Ben
For L2TP that should work very well. But, with other tunnel types like GRE etc.
route lookups have to be done first in the inner and then outer.  It
makes it easier
to keep keep the tunnel in the inner namespace in such cases. right?

thank you
rsa

On Wed, Oct 24, 2012 at 5:21 PM, Benjamin LaHaise <bcrl@...ck.org> wrote:
> On Wed, Oct 24, 2012 at 02:11:14PM -0700, Eric W. Biederman wrote:
>> rsa <ravi.mlists@...il.com> writes:
>>
>> > Assuming I have a tunnel interface where two route lookups are done --
>> > one for innter
>> > packet and the other for outer -- do you see any issues in switching
>> > the network
>> > namespace prior to second route lookup (and restore to the original namespace
>> > after the second lookup is done)?
>> >
>> > If so, are there any other calls other than sk_change_net() needed?
>>
>> In general sk_change_net is a bad idea.
>>
>> Most likely what you want to do is simply memorize both struct net's
>> that you care about and perform the routing lookup as appropriate.
>>
>> Certainly you don't want to be calling sk_change_net for every packet
>> that goes through your tunnel.
>
> I've actually done this with L2TP.  The packets coming into the system from
> the tunnel are received on one UDP socket in one "struct net", but the
> decapsulated packets are received on a "struct net_device" that is in a
> different "struct net".  No special coding is required -- just move the
> tunnel's net_device into another namespace after creation and it works as
> expected.  Using sk_change_net() would be full of races and is really not
> required for the vast majority of use cases.
>
>                 -ben
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