Subject: Re: [PATCH] net: ipv6: Make address flushing on ifdown optional

From: YOSHIFUJI Hideaki <[email-masked]>
Date: Wed, 17 Feb 2016 11:10:43 +0900

Hi,

David Ahern wrote:
> On 2/16/16 1:45 AM, YOSHIFUJI Hideaki wrote:
>>> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
>>> index 24ce97f42d35..7ddbbb67f0db 100644
>>> --- a/Documentation/networking/ip-sysctl.txt
>>> +++ b/Documentation/networking/ip-sysctl.txt
>>> @@ -1563,6 +1563,12 @@ temp_prefered_lft - INTEGER
>>>   	Preferred lifetime (in seconds) for temporary addresses.
>>>   	Default: 86400 (1 day)
>>>   
>>> +keep_addr_on_down - BOOLEAN
>>> +	Keep all IPv6 addresses on an interface down event. If set static
>>> +	global addresses with no expiration time are not flushed.
>>> +
>>> +	Default: disabled
>>> +
>>
>> How about this:
>>     1: enabled
>>     0: system default
>>    -1: disabled
>> so that an iterface can override system-wide config?
> 
> It is my understanding that the 'all' settings override the individual
> interface settings. From Documentation/networking/ip-sysctl.txt +1346:
> 
> conf/all/*:
>         Change all the interface-specific settings.

Well, document is not correct.
1) Some of "all" variables set all interface specific settings.
2) Some of "all" variables override interface specific settings.
3) Some provide "fall-back" values; such an interface specific
   setting overrides the corresponding "all" variable.
   (Note: "default" variables are values per-interface settings
   are initialized to.)
4) Others are ignored (the exists but no-ops).

> 
> 
> -----8<-----
> 
> 
>>> diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
>>> index 1c8b6820b694..01ba6a286a4b 100644
>>> --- a/include/net/if_inet6.h
>>> +++ b/include/net/if_inet6.h
>>> @@ -72,6 +72,7 @@ struct inet6_ifaddr {
>>>   	int			regen_count;
>>>   
>>>   	bool			tokenized;
>>> +	bool			user_managed;
>>
>> Can't we use IFA_F_PERMANENT?
> 
> I think so. Will fix.
> 
> 
> -----8<-----
> 
>>> @@ -3356,7 +3413,9 @@ static int addrconf_ifdown(struct net_device *dev, int how)
>>>   {
>>>   	struct net *net = dev_net(dev);
>>>   	struct inet6_dev *idev;
>>> -	struct inet6_ifaddr *ifa;
>>> +	struct inet6_ifaddr *ifa, *tmp;
>>> +	struct list_head del_list;
>>> +	int keep_addr;
>>>   	int state, i;
>>>   
>>>   	ASSERT_RTNL();
>>> @@ -3383,6 +3442,10 @@ static int addrconf_ifdown(struct net_device *dev, int how)
>>>   
>>>   	}
>>>   
>>> +	keep_addr = net->ipv6.devconf_all->keep_addr_on_down;
>>> +	if (!keep_addr)
>>> +		keep_addr = idev->cnf.keep_addr_on_down;
>>> +
>>>   	/* Step 2: clear hash table */
>>>   	for (i = 0; i < IN6_ADDR_HSIZE; i++) {
>>>   		struct hlist_head *h = &inet6_addr_lst[i];
> 
> So what I have here is if the system-wide setting says keep the address
> it is kept. Else if the individual interface setting is enabled the
> address is kept.
> 
> 
> 

Other admin may want to enable it system-wide with some exceptions.

And well, you could just check per-interface configuration; 4 above.

-- 
Hideaki Yoshifuji <[email-masked]>
Technical Division, MIRACLE LINUX CORPORATION