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

On 08/31/2011 02:36 PM, Ben Hutchings wrote:

On Wed, 2011-08-31 at 13:48 -0700, Ben Greear wrote:

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On 08/31/2011 01:31 PM, Nicolas de Pesloüan wrote:

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Le 31/08/2011 22:12, Ben Hutchings a écrit :

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On Wed, 2011-08-31 at 22:03 +0200, Nicolas de Pesloüan wrote:

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Le 31/08/2011 10:45, Jiri Pirko a écrit :

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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.

There is special hardware out there that can do bypass, and often it also has a mode
that will programatically cut link by throwing some relays.  We use this for our
testing equipment...

If there is some way to twiddle standard-ish hardware to actually drop link, that
would be neat.  I'd think it should be an ethtool type of thing, however.

We need to be able to control this as part of our driver test suite (on
the peer, not the device under test).  There are various MDIO bits that
look like they should do this but unfortunately they don't have
consistent effects.  Besides that, many PHYs are not MDIO-manageable.
So this would have to be a device-specific operation, whether it's
exposed through ethtool or sysfs.

Well, I have boxes that can act as the peer.  Nics are intel chipset 1G,
the bypass/link-drop feature is some separate hardware on the NIC, and
there is a hack of a driver & user-space tools that controls those bits.

But, if there is a way to fiddle normal NICs w/out the special bypass/disconnect
hardware, that would be welcome.  Even if it's different for each driver, and
not supported by all, ethtool can deal with that sort of thing.

Here's a link to the hardware we use...it comes with drivers, though we've hacked on
ours a bit.

http://silicom-usa.com/upload/Downloads/Product_102.pdf

Thanks,
Ben

-- 
Ben Greear [off-list ref]
Candela Technologies Inc  http://www.candelatech.com