netdev - Re: [PATCH net-next] bridge: fix setlink/dellink notifications

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Date:	Wed, 14 Jan 2015 15:56:02 -0800
From:	roopa <roopa@...ulusnetworks.com>
To:	John Fastabend <john.fastabend@...il.com>
CC:	"Arad, Ronen" <ronen.arad@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"shemminger@...tta.com" <shemminger@...tta.com>,
	"vyasevic@...hat.com" <vyasevic@...hat.com>,
	"tgraf@...g.ch" <tgraf@...g.ch>,
	"jhs@...atatu.com" <jhs@...atatu.com>,
	"sfeldma@...il.com" <sfeldma@...il.com>,
	"jiri@...nulli.us" <jiri@...nulli.us>,
	"wkok@...ulusnetworks.com" <wkok@...ulusnetworks.com>
Subject: Re: [PATCH net-next] bridge: fix setlink/dellink notifications

On 1/14/15, 3:36 PM, John Fastabend wrote:
> On 01/14/2015 03:22 PM, Arad, Ronen wrote:
>>
>>
>>> -----Original Message-----
>>> From: netdev-owner@...r.kernel.org 
>>> [mailto:netdev-owner@...r.kernel.org] On
>>> Behalf Of roopa@...ulusnetworks.com
>>> Sent: Tuesday, January 13, 2015 10:49 PM
>>> To: netdev@...r.kernel.org; shemminger@...tta.com; vyasevic@...hat.com;
>>> john.fastabend@...il.com; tgraf@...g.ch; jhs@...atatu.com; 
>>> sfeldma@...il.com;
>>> jiri@...nulli.us
>>> Cc: wkok@...ulusnetworks.com
>>> Subject: [PATCH net-next] bridge: fix setlink/dellink notifications
>>>
>>> From: Roopa Prabhu <roopa@...ulusnetworks.com>
>>>
>> [..]
>
> [...]
>
>>>             err = dev->netdev_ops->ndo_bridge_setlink(dev, nlh);
>>> -
>>> -        if (!err)
>>> +        if (!err) {
>>>             flags &= ~BRIDGE_FLAGS_SELF;
>>> +
>>> +            /* Generate event to notify upper layer of bridge
>>> +             * change
>>> +             */
>>> +            if (!err)
>>> +                err = rtnl_bridge_notify(dev, oflags);
>>> +        }
>>>     }
>>>
>>>     if (have_flags)
>>>         memcpy(nla_data(attr), &flags, sizeof(flags));
>>
>> What is the purpose of the above two lines (not changed by the patch)?
>> They seem to copy over the flags with the successfully applied cases
>> (MASTER and/or SELF) flags cleared back into the incoming netlink 
>> message.
>> I could not figure any place where the modified flags attribute is used
>
> This allows userspace to learn which operation failed when it is an
> operation to set both the software bridge via BRIDGE_FLAGS_MASTER and
> the the hardware via BRIDGE_FLAGS_SELF. When we get the error back
> software looks at the flags to figure out how to recover/retry/etc.
Ah ok, I was also wondering why that was there,

thanks,
Roopa

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