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

[Alexey Kuznetsov]

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).

Alexey
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