netdev - Re: namespace support requires network modules to say "GPL"

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Message-ID: <4755AC13.1060904@candelatech.com>
Date:	Tue, 04 Dec 2007 11:35:47 -0800
From:	Ben Greear <greearb@...delatech.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Daniel Lezcano <daniel.lezcano@...e.fr>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, containers@...ts.osdl.org,
	Mark Lord <lkml@....ca>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Subject: Re: namespace support requires network modules to say "GPL"

Eric W. Biederman wrote:
> Ben Greear <greearb@...delatech.com> writes:
> 
>> Eric W. Biederman wrote:
>>> However there also seem to be simpler cases like Ben's bridge module,
>>> that don't appear to have any global state.
>>>
>> Well, my module has some global state, but I don't think it needs to care about
>> namespaces.  My first impression is that my module should be able to bridge
>> namespaces...not be contained within one.  I can have user-space make sure that
>> I don't bridge between
>> devices in different name-spaces, or perhaps bridging between namespaces
>> wouldn't be a problem anyway. 
> 
> Bridging between namespaces should not be a problem, but it could be
> a bit of a challenge to setup (in finding the network devices).
> Probably the easy way is to setup the bridging and then move one of the
> network devices to the other network namespace.
> 
> Essentially bridging between two network devices in two network
> namespaces looks like bridging between two network devices on two
> separate network stacks.   Although internally things look a little
> better.

Ok, that sounds fine.

>> Currently I use procfs and ioctls bound to a procfs file descriptor.
> 
> Which is where it gets tricky   You are defining new userspace ABIs.
> I can see where they occasionally make sense during development
> and prototyping but long term out of tree userspace interfaces appear
> to me to be a real maintenance problem.

They are completely contained within my module, and no one is going
to change my module w/out me knowing, so actually I have very little
problem here :)

>> For namespaces in general, will there be a way to just do a dev_get_by_* and
>> find the
>> device in *any* namespace and query the device to see what namespace it is in?
>> Then my module or some other more clever piece of code can determine the
>> namespaces
>> (by comparing pointers if nothing else) and make proper decision.  For instance,
>> maybe
>> we want to bridge two namespaces, or maybe we want to forbid that ever
>> happening...
> 
> The issue is that fundamentally all userspace device identifiers can
> be duped between namespaces.  So since there is no unique identifier
> we can not implement a function to do that.

Ok, but can a netdev at least know what namespace it is in?  I don't
need this for my module, but it seems very useful knowledge...

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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