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

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Date:	Wed, 31 Aug 2011 21:44:40 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.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

On Wed, 2011-08-31 at 22:31 +0200, Nicolas de Pesloüan wrote:
> 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.

Think what happens if the user sets carrier on, when the link is
actually down.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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