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

[Jiri Pirko <jpirko@redhat.com>]

Wed, Aug 31, 2011 at 11:40:23PM CEST, shemminger@vyatta.com wrote:
>On Wed, 31 Aug 2011 22:36:45 +0100
>Ben Hutchings <bhutchings@solarflare.com> wrote:
>
>> On Wed, 2011-08-31 at 13:48 -0700, Ben Greear wrote:
>> > On 08/31/2011 01:31 PM, 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.
>> > 
>> > 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.
>> 
>> > Actually dropping link, and letting that naturally propagate up the stack seems
>> > more reasonable than lying about the status half way up the stack.
>> 
>
>For testing clustering, there are hooks in vmware and QEMU/KVM to allow
>dropping carrier on the VM side.

Afaik in kvm this is only possible on emulated e1000 (last time I
checked).