Re: [RFC] cfg80211: allow userspace to take ownership of interfaces

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2014-03-24 at 18:35 +0100, Arend van Spriel wrote:

> > To avoid this problem, introduce an ownership concept for interfaces. If
> > an interface is owned by a netlink socket, then it will be destroyed if
> > the netlink socket is closed for any reason, including if the process it
> > belongs to crashed. This gives us a race-free way to get rid of any such
> > interfaces.
> 
> Excellent idea.

:)

> > + * @NL80211_ATTR_IFACE_SOCKET_OWNER: flag attribute, if set during interface
> > + *	creation then the new interface will be owned by the netlink socket
> > + *	that created it and will be destroyed when the socket is closed
> > + *
> 
> Guess you want explicit flag so apps like iw can still create 
> interfaces, right?

Right, otherwise iw exits and the interface is destroyed immediately (I
did that for my testcase :) )

> > @@ -11662,6 +11675,19 @@ static int nl80211_netlink_notify(struct notifier_block * nb,
> >   			}
> >   		}
> >   		spin_unlock_bh(&rdev->beacon_registrations_lock);
> > +
> > +		if (schedule_destroy_work) {
> > +			struct cfg80211_iface_destroy *destroy;
> > +
> > +			destroy = kzalloc(sizeof(*destroy), GFP_ATOMIC);
> 
> Probably overlooking it, because it is not part of the patch but: what 
> lock requires this to be atomic? rcu_read_lock?

yes, but even if we moved it out it wouldn't help since it's an atomic
notifier chain

johannes