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Date:	Thu, 07 Jun 2007 18:23:06 +0400
From:	Kirill Korotaev <>
To:	Daniel Lezcano <>
CC:	Pavel Emelianov <>,
	Kirill Korotaev <>,
	Linux Netdev List <>,
	"Eric W. Biederman" <>,
	Linux Containers <>,
	Patrick McHardy <>
Subject: Re: [PATCH] Virtual ethernet tunnel


Daniel Lezcano wrote:
> Pavel Emelianov wrote:
>>>>I did this at the very first version, but Alexey showed me that this
>>>>would be wrong. Look. When we create the second device it must be in
>>>>the other namespace as it is useless to have them in one namespace.
>>>>But if we have the device in the other namespace the RTNL_NEWLINK
>>>>message from kernel would come into this namespace thus confusing ip
>>>>utility in the init namespace. Creating the device in the init ns and
>>>>moving it into the new one is rather a complex task.
>>>moving the netdevice to another namespace is not a complex task. Eric
>>>Biederman did it in its patchset ( cf. )
>>By saying complex I didn't mean that this is difficult to implement,
>>but that it consists (must consist) of many stages. I.e. composite.
>>Making the device right in the namespace is liter.
>>>When the pair device is created, both extremeties are into the init
>>>namespace and you can choose to which namespace to move one extremity.
>>I do not mind that.
>>>When the network namespace dies, the netdev is moved back to the init
>>>That facilitate network device management.
>>>Concerning netlink events, this is automatically generated when the
>>>network device is moved through namespaces.
>>>IMHO, we should have the network device movement between namespaces in
>>>order to be able to move a physical network device too (eg. you have 4
>>>NIC and you want to create 3 containers and assign 3 NIC to each of them)
>>Agree. Moving the devices is a must-have functionality.
>>I do not mind making the pair in the init namespace and move the second
>>one into the desired namespace. But if we *always* will have two ends in
>>different namespaces what to complicate things for?
> Just to provide a netdev sufficiently generic to be used by people who 
> don't want namespaces but just want to do some network testing, like Ben 
> Greear does. He mentioned in a previous email, he will be happy to stop 
> redirecting people to out of tree patch.

no one is against generic code and ability to create 2 interfaces in *one* namespace.
(Like we currently allow to do so in OpenVZ)

However, believe me, moving an interface is a *hard* operation. Much harder then netdev
register from the scratch.

Because it requires to take into account many things like:
- packets in flight which requires synchronize and is slow on big machines
- asynchronous sysfs entries registration/deregistration from
  rtln_unlock -> netdev_run_todo
- name/ifindex collisions
- shutdown/cleanup of addresses/routes/qdisc and other similar stuff


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