netdev - Re: Move interface across network namespaces

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Message-ID: <CAChaegm2d3LywMAcq66PgPZwF5Fu=_zuqcTh8VdCG6zvhyPJXQ@mail.gmail.com>
Date:	Thu, 11 Aug 2011 15:29:43 -0300
From:	Renato Westphal <renatowestphal@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Move interface across network namespaces

2011/8/11 Eric W. Biederman <ebiederm@...ssion.com>:
> Renato Westphal <renatowestphal@...il.com> writes:
>
>> Hello,
>>
>> I have two questions regarding the process of moving a network
>> interface across different network namespaces:
>>
>> * When I move an interface, all the virtual interfaces attached to it
>> are deleted. Is there any reason for such odd behavior? I would like
>> to move some network interfaces and keep the attached vlans untouched.
>
> The defined semantics are that a network device is unregistered from
> the networking stack in one network namespace and then registered
> with the networking stack in another.  It is an unfortunate fact
> that when vlan devices see their underlying device being unregistered
> they decide to delete themselves.
>
> A different vlan implementation might be able to have different
> properties but I can't think of any obvious solution other than
> don't do move the device that you have your vlans on top of.
>

Thanks for the info, I can handle with that by modifying my quagga-vrf patches.

>> * The target network namespace sends a RTM_NEWLINK netlink message
>> when an interface is moved to it. In the other hand, the source
>> network namespace doesn't sends a RTM_DELLINK message when an
>> interface is moved from it. This is very annoying because user space
>> applications (such as zebra) can't detect some interface moving
>> operations and then get into an inconsistent state. Anyone knows if
>> there's a workaround for this?
>
> Not getting RTM_DELLINK is a bug.  The device registration and
> unregistration code has changed since dev_change_net_namespace was
> written and apparently one of the changes failed to update
> dev_change_net_namespace.
>

Good, that makes a lot more sense. In the kernel 2.6.32.43 the
RTM_DELLINK netlink message is sent when a network interface is moved
from a network namespace. The same doesn't happens in the kernel
2.6.35.13. I'll try to isolate the problem some more.

Best Regards,
Renato.

-- 
Renato Westphal
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