[Devel] Re: [PATCH] netns: Delete virtual interfaces during namespace cleanup

[Pavel Emelyanov]

Daniel Lezcano wrote:
> Eric W. Biederman wrote:
>> When physical devices are inside of network namespace and that
>> network namespace terminates we can not make them go away.  We
>> have to keep them and moving them to the initial network namespace
>> is the best we can do.
>>
>> For virtual devices left in a network namespace that is exiting
>> we have no need to preserve them and we now have the infrastructure
>> that allows us to delete them.  So delete virtual devices when we
>> exit a network namespace.  Keeping the necessary user space clean up
>> after a network namespace exits much more tractable.
>>
>> This patch removes much of the need for user space clean up code to
>> run after a network namespace exits.
> 
> I agree that will make the life easier for user space developer :)
> 
> I have a few questions about this new behaviour.
> 
> After discussing with Benjamin, this patch means an user can no longer 
> manage a pool of virtual devices because they will be automatically 
> destroyed when the namespace exits. I don't think it is a big concern, 
> but just in case I am asking :)
> 
> Another point, at present, the virtual devices go back to the initial 
> network namespace when the namespace dies, and this behaviour is used to 
> track the namespace life cycle. With this patch we have no way to know 
> when the network namespace has exited. So we can have the last process 
> exiting the network namespace, but the network namespace can stay alive 
> (eg. some sockets still have buffer to send) ?
> 
> AFAIR, Pavel told us about a patch extending the "wait" semantic and 
> pass namespace options to wait for. Is that right Pavel ? Shouldn't we 
> apply this path before deleting the virtual network devices ?

I remember that I promised to prepare the wait-extending patch. But I
haven't manage to find time for this, sorry :( In a month or two I will
finish one time-hungry task and hopefully be able to do it.

As far as this particular patch is concerned.

All the virtual devices we have now in namespaces (vlan and tunnels)
kill themselves *before* this code is called. But even if we try to
move this destruction from modules to here, we'll be in a tricky
situation, when the e.g. ipip module has already kfree-d the net_ipip
structure, while none of ipip devices are released yet.

If we try to look in the future - if we ever have a virtual device
driver, that will be able to create its devices in namespace, we'll
have to destroy all these devices *before* (or inside) this driver's
net->exit callback is called, but this patch dies the ->dellink call
at the very end, i.e. *after* any potential ->exit callback.

Eric - did you see any device, that was ->dellink-ed by this patch?

> Thanks.
>    -- Daniel
> 
>> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
>> ---
>>  net/core/dev.c |    6 ++++++
>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 7091040..f3476d4 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -4844,6 +4844,12 @@ static void __net_exit default_device_exit(struct net *net)
>>  		if (dev->features & NETIF_F_NETNS_LOCAL)
>>  			continue;
>>
>> +		/* Delete virtual devices */
>> +		if (dev->rtnl_link_ops && dev->rtnl_link_ops->dellink) {
>> +			dev->rtnl_link_ops->dellink(dev);
>> +			continue;
>> +		}
>> +
>>  		/* Push remaing network devices to init_net */
>>  		snprintf(fb_name, IFNAMSIZ, "dev%d", dev->ifindex);
>>  		err = dev_change_net_namespace(dev, &init_net, fb_name);
> 

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