netdev - Re: [patch net-next-2.6] net: allow notifier subscribers to forbid device from closing

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Date:	Wed, 31 Aug 2011 18:22:50 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org,
	davem@...emloft.net, eric.dumazet@...il.com
Subject: Re: [patch net-next-2.6] net: allow notifier subscribers to forbid
 device from closing

Wed, Aug 31, 2011 at 05:53:38PM CEST, shemminger@...tta.com wrote:
>On Wed, 31 Aug 2011 16:25:51 +0100
>Ben Hutchings <bhutchings@...arflare.com> wrote:
>
>> On Wed, 2011-08-31 at 17:15 +0200, Jiri Pirko wrote:
>> > In some situations, like when the device is used as slave device in
>> > bond/br/etc it is not nice if someone closes the device. This allows
>> > it's masters to forbid this closure.
>> 
>> No it doesn't.
>> 
>> [...]
>> > @@ -1269,9 +1282,12 @@ static int dev_close_many(struct list_head *head)
>> >  	struct net_device *dev, *tmp;
>> >  	LIST_HEAD(tmp_list);
>> >  
>> > -	list_for_each_entry_safe(dev, tmp, head, unreg_list)
>> > +	list_for_each_entry_safe(dev, tmp, head, unreg_list) {
>> >  		if (!(dev->flags & IFF_UP))
>> >  			list_move(&dev->unreg_list, &tmp_list);
>> > +		else
>> > +			__dev_pre_close(dev);
>> > +	}
>> >  
>> >  	__dev_close_many(head);
>> 
>> The return value is ignored here.
>> 
>> And this is called from dev_close(), where you are adding the
>> notification as well.  So the notifier will usually be called twice.
>> 
>> [...]
>> > @@ -1397,6 +1418,7 @@ rollback:
>> >  				break;
>> >  
>> >  			if (dev->flags & IFF_UP) {
>> > +				nb->notifier_call(nb, NETDEV_PRE_DOWN, dev);
>> >  				nb->notifier_call(nb, NETDEV_GOING_DOWN, dev);
>> >  				nb->notifier_call(nb, NETDEV_DOWN, dev);
>> >  			}
>> [...]
>> 
>> The return value has to be ignored here.  Not sure it makes any sense to
>> call the notifier at all.
>> 
>> Ben.
>> 
>
>Also we need to allow rmmod'ing a network device even it is
>part of a bridge and that implicitly
>calls close.


this is not a problem because when it's called from
rollback_registered_many, return value if pre_down is ignored.
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