netdev - Re: [PATCH] bonding:update speed/duplex for NETDEV

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Date:	Mon, 31 Oct 2011 22:41:39 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jay Vosburgh <fubar@...ibm.com>
CC:	Weiping Pan <wpan@...hat.com>, <netdev@...r.kernel.org>,
	<andy@...yhouse.net>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bonding:update speed/duplex for NETDEV_CHANGE

On Mon, 2011-10-31 at 14:23 -0700, Jay Vosburgh wrote:
> Ben Hutchings <bhutchings@...arflare.com> wrote:
> 
> >On Mon, 2011-10-31 at 13:32 -0700, Jay Vosburgh wrote:
> >[...]
> >> 	This particular case arises only during enslavement.  The call
> >> to bond_update_speed_duplex call has failed, but the device is marked by
> >> bonding to be up.  Bonding complains that the device isn't down, but it
> >> cannot get speed and duplex, and therefore is assuming them to be
> >> 100/Full.
> >> 
> >> 	The catch is that this happens only for the ARP monitor, because
> >> it initially presumes a slave to be up regardless of actual carrier
> >> state (for historical reasons related to very old 10 or 10/100 drivers,
> >> prior to the introduction of netif_carrier_*).
> >
> >Right, I gathered that.  Is there any reason to use the ARP monitor when
> >all slaves support link state notification?  Maybe the bonding
> >documentation should recommend miimon in section 7, not just in section
> >2.
> 
> 	The ARP monitor can validate that traffic actually flows from
> the slave to some destination in the switch domain (and back), so, for
> example, it's useful in cases that multiple switch hops exist between
> the host and the local router.  A link failure in the middle of the path
> won't affect carrier on the local device, but still may cause a
> communications break.

Then the ARP monitor should gracefully handle the case where a new slave
has link down, as proposed.

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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