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

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Date:	Mon, 31 Oct 2011 18:15:06 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Weiping Pan <wpan@...hat.com>
CC:	<netdev@...r.kernel.org>, <fubar@...ibm.com>, <andy@...yhouse.net>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bonding:update speed/duplex for NETDEV_CHANGE

On Mon, 2011-10-31 at 22:19 +0800, Weiping Pan wrote:
> Zheng Liang(lzheng@...hat.com) found a bug that if we config bonding with
> arp monitor, sometimes bonding driver cannot get the speed and duplex from
> its slaves, it will assume them to be 100Mb/sec and Full, please see
> /proc/net/bonding/bond0.
> But there is no such problem when uses miimon.
> 
> (Take igb for example)
> I find that the reason is that after dev_open() in bond_enslave(),
> bond_update_speed_duplex() will call igb_get_settings()
> , but in that function,
> it runs ethtool_cmd_speed_set(ecmd, -1); ecmd->duplex = -1;
> because igb get an error value of status.
> So even dev_open() is called, but the device is not really ready to get its
> settings.
> 
> Maybe it is safe for us to call igb_get_settings() only after
> this message shows up, that is "igb: p4p1 NIC Link is Up 1000 Mbps Full Duplex,
> Flow Control: RX".
[...]

For any device with autonegotiation enabled, you generally cannot get
the speed and duplex settings until the link is up.  While the link is
down, you may see a value of 0, ~0, or the best mode currently
advertised.  So I think that the bonding driver should avoid updating
the slave speed and duplex values whenever autoneg is enabled and the
link is 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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