netdev - Re: [PATCH net RESEND] bonding: don't change to 802.3ad mode while ARP monitoring is running

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Date:	Mon, 18 Nov 2013 21:31:38 -0500
From:	Andy Gospodarek <andy@...yhouse.net>
To:	Dan Williams <dcbw@...hat.com>, David Miller <davem@...emloft.net>
CC:	dingtianhong@...wei.com, fubar@...ibm.com, nikolay@...hat.com,
	vfalico@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net RESEND] bonding: don't change to 802.3ad mode while
 ARP monitoring is running

On 11/18/2013 05:50 PM, Dan Williams wrote:
> On Mon, 2013-11-18 at 15:48 -0500, David Miller wrote:
>> From: Dan Williams <dcbw@...hat.com>
>> Date: Mon, 18 Nov 2013 11:44:42 -0600
>>
>>> On Sat, 2013-11-16 at 14:30 +0800, Ding Tianhong wrote:
>>>> Because the ARP monitoring is not support for 802.3ad, but I still
>>>> could change the mode to 802.3ad from ab mode while ARP monitoring
>>>> is running, it is incorrect.
>>>>
>>>> So add a check for 802.3ad in bonding_store_mode to fix the problem,
>>>> and make a new macro BOND_NO_USES_ARP() to simplify the code.
>>> Instead of failing, couldn't the code stop ARP monitoring and allow the
>>> mode change?  This is similar to setting miimon, which disables ARP
>>> monitoring, or setting ARP monitoring, which disables miimon.
>>>
>>> 	if (new_value && bond->params.arp_interval) {
>>> 		pr_info("%s: MII monitoring cannot be used with ARP monitoring. Disabling ARP monitoring...\n",
>>> 			bond->dev->name);
>>> 		bond->params.arp_interval = 0;
>>> 		if (bond->params.arp_validate)
>>> 			bond->params.arp_validate = BOND_ARP_VALIDATE_NONE;
>>> 	}
>>>
>>> Bond mode is the most important bond option, so it seems like it should
>>> override any of the other sub-options.  I know the code doesn't do this
>>> now, but maybe instead of the patch you propose, it would be nicer to
>>> allow the mode change instead?
>> I agree with Dan, if other mode changes behave this way (by dropping the
>> incompatible feature) we should make 802.3ad do so as well at the very
>> least for consistency.
> Currently ALB and TLB modes will fail if arp_interval > 0, so Ding's
> patch is technically correct.
>
> Instead, I'm proposing that 'mode' trumps all, and if the user changes
> the mode, conflicting values should be cleared or reset.  Otherwise
> userspace has to duplicate a lot of kernel logic/validation.  For
> example:
>
> 1) set mode to ROUNDROBIN
> 2) set arp_interval
> 3) set mode to ALB or TLB
> 4) FAIL - incompatible with arp_interval
> 5) ok, set arp_interval to zero
> 6) set mode to ALB or TLB
> 7) SUCCESS
>
> Wouldn't it be nice if the kernel handled clearing arp_interval for us,
> since it knows that arp_interval is incompatible with ALB/TLB...
>
> Could be done separately.  I have no objection to Ding's patch other
> than "life could be even better".
>
> Dan
Nik was actually planning to work on a pretty significant rewrite of the 
code that handles setting and clearing of different config options, but 
I have not seen him chime in on this thread yet.

Nik, anything you can share on this or are you still a bit away from 
coming up with a design and implementation?

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