netdev - Re: [patch 1/1][NETNS][IPV6] protect addrconf from loopback registration

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Message-Id: <20071112.142455.73541417.davem@davemloft.net>
Date:	Mon, 12 Nov 2007 14:24:55 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	den@...ru
Cc:	dlezcano@...ibm.com, netdev@...r.kernel.org, xemul@...nvz.org,
	ebiederm@...ssion.com, containers@...ts.osdl.org,
	yoshfuji@...ux-ipv6.org, benjamin.thery@...l.net
Subject: Re: [patch 1/1][NETNS][IPV6] protect addrconf from loopback
 registration

From: "Denis V. Lunev" <den@...ru>
Date: Mon, 12 Nov 2007 19:49:03 +0300

> Unregister for a loopback in !init_net is a _valid_ operation and should
> be clean, i.e. without kludges in the path. This is the only way to
> check the ref-counting.

For ipv6 the stack really wants to pin down the loopback
device because we need a valid inet6_dev object to reference
at all times in order to simplify the per-device SNMP
statistic bumping.

When a non-loopback device goes down, we point any existing
references to that device's idev to the loopback one instead.

I really consider taking down the loopback device to be
an invalid operation at least how things are implemented
currently.

There was a suggestion to have a "dummy" device that takes the
place of "point dangling idev refs to loopback's one".  But
some people get upset when statistical events get lost, and
rightly so.  Such a dummy device would either need to be
invisible to the user, or show up and be utterly confusing.

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