Re: [B.A.T.M.A.N.] [PATCH 1/4] batman-adv: NETIF_F_NETNS_LOCAL feature to prevent netns moves

[Antonio Quartulli <a@unstable.cc>]

On Sat, Jan 23, 2016 at 06:20:06PM +0100, Andrew Lunn wrote:
> On Sat, Jan 23, 2016 at 10:06:37AM +0800, Antonio Quartulli wrote:
> > On Wed, Jan 20, 2016 at 06:48:27PM +0100, Andrew Lunn wrote:
> > > The batX soft interface should not be moved between network name
> > > spaces. This is similar to bridges, bonds, tunnels, which are not
> > > allowed to move between network namespaces.
> > > 
> > 
> > Andrew,
> > I understand bridges and other similar interfaces do the same, but what
> > is the real reason for preventing a batman soft-interface from moving
> > between namespaces?
> 
> Humm, actually, a good question. I blindly copied this code without
> thinking about it.
> 
> One clear answer is the notification mechanism, used by
> batadv_hard_if_event(). As far as i can see, such events are only sent
> within the interfaces namespace. So for example you hot unplug a hard
> interface which the soft interface is using, you would not get the
> NETDEV_DOWN event if the soft interface is in a different namespace.

This raises another question (maybe addressed by another of your patch?): what
happens if an hard-interface currently enslaved in bat0 changes namespace?
Will this result in an UNREGISTER event like when the interface gets destroyed?
If not, I am not sure how the whole situation can still be consistent.

> 
> Now that i think of it, there are a few other reasons. All the
> interface management calls, and displaying of interface names would
> have to contains the namespace. Otherwise you look at the output for
> 'batctl o' and have no idea which namespace that wlan0 interface is
> from. Remember, interface names are only unique within a namespace,
> not across namespaces.

Yeah, it make sense. If the softif is in the same ns as the hardifs, it is
definitely necessary to prevent bat0 from jumping from a namespace to another.

Cheers,

-- 
Antonio Quartulli