netdev - Re: [RFC] bridge: MAC learning uevents

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Date:   Fri, 9 Sep 2016 10:51:31 +0200
From:   "D. Herrendoerfer" <d.herrendoerfer@...rendoerfer.name>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Subject: Re: [RFC] bridge: MAC learning uevents



> On Thu, 8 Sep 2016 11:30:08 -0700
> Florian Fainelli <f.fainelli@...il.com> wrote:
> 
>> On 09/08/2016 10:19 AM, D. Herrendoerfer wrote:
>>> 
>>> On 08 Sep 2016, at 17:39, Stephen Hemminger <stephen@...workplumber.org> wrote:
>>> 
>>>> On Thu, 8 Sep 2016 15:06:16 +0200
>>>> "D. Herrendoerfer" <d.herrendoerfer@...rendoerfer.name> wrote:
>>>> 
>>>>> Hello,
>>>>> 
>>>>> I'd like to start a discussion if it makes sense to add an optional feature
>>>>> 
>>>>> to the bridge MAC address learning code to generate kernel uevents for  
>>> 
>>> [SNIP]
>>> 
>>>>> 
>>>>> I'm porting my patch (for 3.10.0) to head, and will make it available, I 
>>>>> just want some
>>>>> 
>>>>> valuable feedback as early as possible.
>>>>> 
>>>>> 
>>>>> Thanks, D.Herrendoerfer  
>>>> 
>>>> This should be possible by listening for netlink events.
>>>> No need for udev interaction.  
>>> 
>>> No, there are none, not for changes to the bridge forwarding table, also this would 
>>> require a tool to continuously listen for changes.  
>> 
>> Wat do you expect uevent to solve here that netlink + a monitoring
>> program can't?
>> 
>> There is quite a bit of code in net/bridge/br_fdb.c just to deal with
>> notifying learned/added MAC addresses, is not that where you should
>> start adding what you are after (if that is not supported as of latest
>> mainline)?
> 
> just like neighbor table modifications, it should be possible to listen for
> events with netlink. Doing it through uevent is the wrong model.

I agree partially - but consider:
we plug hardware - we get an event
we remove hardware - we get an event
we add a virtual interface - we get an event
we add a bridge - event
we add an interface to that bridge - event 
a kvm guest starts using the interface on that bridge - we need to monitor netlink, poll brforward, capture traffic

It seems inconsistent, bridge is already emitting events.