netdev - Last Ipv6 address removal causes "addrconf_sysctl_unregister", which inihibits from changing disable

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Message-ID: <AANLkTimnBssEeO_faqcAAzHCy8KxQo9FVcn7vu5fru4j@mail.gmail.com>
Date:	Mon, 26 Jul 2010 10:03:13 -0400
From:	Mahesh Kelkar <maheshkelkar@...il.com>
To:	Brian Haley <brian.haley@...com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Last Ipv6 address removal causes "addrconf_sysctl_unregister", which 
	inihibits from changing disable_ipv6 setting

Odd behavior associated with the patch:
**Last address removal causes "addrconf_sysctl_unregister", which
inihibits from changing disable_ipv6 setting
(connected issue: With disable_ipv6 set to 1 on an interface, ff00:/8
and fe80::/64 are still added on device UP)

Current sysctl config:
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

Steps:
- Remove last IPv6 address assigned to the "eth0" interface
- inet6_addr_del => addrconf_ifdown(idev->dev, 1) => does the device
sysctl unregister
******Not sure why the addrconf_sysctl_unregister is necessary on last
address removal*******
- Now, "sysctl -a" does not show "net.ipv6.conf.eth0.disable_ipv6"

Problem:
- If you WANT to assign IPv6 address to eth0,
-> Do it once, which fails due to "disable_ipv6" check in
addrconf_add_dev OR ipv6_add_addr
-> But, this process does "addrconf_sysctl_register" (addrconf_add_dev
=> ipv6_find_idev => ipv6_add_dev)
-> set net.ipv6.conf.eth0.disable_ipv6=0 and then successfully assign
ipv6-address to the eth0
(Another alternative is to change all or default to 1; but I wanted to
disable ipv6 by default)

===============
Probable Solution:
===============
@@ -1948,7 +1959,7 @@ static int inet6_addr_del(int ifindex, s
 			   disable IPv6 on this interface.
 			 */
 			if (idev->addr_list == NULL)
-				addrconf_ifdown(idev->dev, 1);
+				addrconf_ifdown(idev->dev, 0);
 			return 0;
 		}
 	}
I have tested the above solution and it seems to work fine - so far.
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