From: Nicolas Dichtel <redacted>
Date: Thu, 15 Jan 2015 15:11:14 +0100

The goal of this serie is to be able to multicast netlink messages with an
attribute that identify a peer netns.
This is needed by the userland to interpret some information contained in
netlink messages (like IFLA_LINK value, but also some other attributes in case
of x-netns netdevice (see also
http://thread.gmane.org/gmane.linux.network/315933/focus=316064 and
http://thread.gmane.org/gmane.linux.kernel.containers/28301/focus=4239)).

Ids of peer netns can be set by userland via a new rtnl cmd RTM_NEWNSID. When
the kernel needs an id for a peer (for example when advertising a new x-netns
interface via netlink), if the user didn't allocate an id, one will be
automatically allocated.
These ids are stored per netns and are local (ie only valid in the netns where
they are set). To avoid allocating an int for each peer netns, I use
idr_for_each() to retrieve the id of a peer netns. Note that it will be possible
to add a table (struct net -> id) later to optimize this lookup if needed.

Patch 1/4 introduces the rtnetlink API mechanism to set and get these ids.
Patch 2/4 and 3/4 implements an example of how to use these ids when advertising
information about a x-netns interface.
And patch 4/4 shows that the netlink messages can be symetric between a GET and
a SET.

 ...

Seires applied, thanks.