Re: [PATCH] ipv6: fix incorrect unregistration of sysctl when last ip deleted

[Eric W. Biederman]

Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx> writes:

> On Fri, Apr 29, 2011 at 02:58:24PM -0700, John Gardiner Myers wrote:
>> If the device isn't going away, then the ip6_ptr shouldn't be zeroed, 
>> the /proc/net/dev_snmp6 entry shouldn't be deregistered,
>
> Actually, you are right. Tuned interface parameters and disabling/enabling IPv6
> (or IP, or whatever) should be different things. We just did not have an interface
> to disable protocol, but leave in*_dev, so that they were merged.
>
> When doing this just keep in mind that addrconf_ifdown(how = 0) did _not_ mean
> disabling IPv6. (Probably, it does now in fact, I do not know. But it definitely
> did not mean this in the past).
>
> Look, addrconf_ifdown(how = 0) was executed only when the physical device is down, so that we could
> neither receive nor send over this interface. If the device is UP, addrconf_ifdown(how = 0)
> did not prohibit sending/receiving IPv6. Actually, logically, addrconf_ifdown(how = 0)
> on UP interface must be followed by immediate restart of autoconfiguration,
> because interface is still actually UP. See?
>
> So, to implement this you should verify that IPv6 packets are not sent/received over
> disabled interface (at least over interface with illegal mtu :-)). And add some flag in in6_dev
> meaning that IPv6 is actually disabled. So that f.e. after occasional
> ifconfig eth0 down; ifconfig eth0 up autoconfiguration would not resume IPv6
> (the thing which we could not even implement with destroying in6_dev,
> but definitely wanted).

I played with this a while ago with on 2.6.37 and I cooked up the patch
below.  I don't know if it still applies, but I think something like
this is what we want, as it makes the no ipv6 address case and the
ipv6 mtu too small case match the disable_ipv6 case.

Eric