Subject: Re: [PATCH] Virtual ethernet tunnel

From: Kirill Korotaev <[email-masked]>
Date: Thu, 07 Jun 2007 18:23:06 +0400

Deniel,

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.
>>>>  
>>>>      
>>>
>>>Pavel,
>>>
>>>moving the netdevice to another namespace is not a complex task. Eric
>>>Biederman did it in its patchset ( cf.  http://lxc.sf.net/network )
>>>    
>>
>>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
>>>namespace.
>>>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.
> 
> https://lists.linux-foundation.org/pipermail/containers/2007-April/004420.html

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

Thanks,
Kirill