netdev - wireless vs. network namespaces (part II)

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Date:	Sat, 27 Sep 2008 12:01:25 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>, Jouni Malinen <j@...fi>
Subject: wireless vs. network namespaces (part II)

Eric,

You wrote, over a year ago:

> 2) Advanced routing.  Where someone is doing some weird thing like 
>    testing sending packets and receiving them on the same machine.

and I was just thinking of doing exactly that :)

When looking into it, though, I noticed that you can generate some
breakage with wireless and network namespaces: you can move a wireless
netdev to a different namespace and then things will break down because
we internally use init_net to find it.

What I'd like to do in wireless is not allow moving netdevs between
namespaces, but rather move entire hardware devices between namespaces,
I see little value and great pain in trying to support virtual
interfaces from a single physical device showing up in different
namespaces, but I do see value in binding a physical device (wiphy) to a
namespace.

As far as I understand, to disallow moving them, I should set the
NETIF_F_NETNS_LOCAL flag on all devices, although that is sort of a
misnomer then because I'd be using it to indicate 'cannot switch
namespace'. 

To really support this though, it seems we need to
 * put the wiphy list into struct net (this is currently a simple
   list_head, no fancy hashing)
 * give each struct wiphy a backpointer to the struct net, like netdev
   in the netdev struct
 * ensure that all netdevs created for this wiphy will have the right
   netns.

The latter part I'm unsure on, alloc_netdev_mq seems to always use
init_net so I can't put them into the right namespace to start with, but
because they're all "in there together" I can't allow switching
namespaces either.. Ideas?

johannes

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