netdev - Re: [patch net-next-2.6 1/2] net: allow to change carrier via sysfs

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Message-ID: <4E5E9A30.1040105@gmail.com>
Date:	Wed, 31 Aug 2011 22:31:44 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	Jiri Pirko <jpirko@...hat.com>,
	Michał Mirosław <mirqus@...il.com>,
	netdev@...r.kernel.org, davem@...emloft.net,
	eric.dumazet@...il.com, shemminger@...tta.com
Subject: Re: [patch net-next-2.6 1/2] net: allow to change carrier via sysfs

Le 31/08/2011 22:12, Ben Hutchings a écrit :
> On Wed, 2011-08-31 at 22:03 +0200, Nicolas de Pesloüan wrote:
>> Le 31/08/2011 10:45, Jiri Pirko a écrit :
>>
>>>>>> Do you expect drivers using implementation different than just calling
>>>>>> netif_carrier_on/off? Or is it supposed to also e.g. power down PHYs?
>>>>> Yes, generally it can be used also for en/disable phy, for testing
>>>>> purposes if hw and driver would support it.
>>>>
>>>> I'd like to see this working for GRE tunnel devices (for keepalive
>>>> daemon to be able to indicate to routing daemons whether tunnel is
>>>> really working) - implementation would be identical to dummy's case.
>>>> Should I prepare a patch or can I leave it to you?
>>>
>>> Ok, I can include it to this patchset (I'm going to repost first patch
>>> anyway)
>>
>> Can't we assume that the dummy's case is the default behavior and
>> register this default
>> ndo_change_carrier callback for every device ?
>
> You have got to be joking.  No device driver that has real link
> monitoring should use this implementation.

Well, why not? Arguably, this is probably not the feature one would use every day, but...

Testing a cluster reaction to a link down event would be easier if one doesn't need to unplug the 
cable for the test. I understand that one can turn off the switch port (physical or virtual), but 
echo 0 > /sys/class/net/eth0/carrier would be nice too.

Of course, I assume that netif_carrier_on and netif_carrier_off are only called on real link status 
change. So the value written into /sys/class/net/eth0/carrier would stay until the link revert it, 
due to a double status change (up-down-up or down-up-down). But I may miss totally this point.

	Nicolas.
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