netdev - Re: The bonding driver should notify userspace of MAC address change

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Message-ID: <4DA89ADC.7040808@gmail.com>
Date:	Fri, 15 Apr 2011 21:22:04 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Jay Vosburgh <fubar@...ibm.com>
CC:	Michał Górny <mgorny@...too.org>,
	netdev@...r.kernel.org, roy@...ples.name,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: The bonding driver should notify userspace of MAC address change

Le 15/04/2011 20:53, Jay Vosburgh a écrit :
> Nicolas de Pesloüan 	<nicolas.2p.debian@...il.com>  wrote:
>
>> Le 15/04/2011 18:44, Michał Górny a écrit :
>>> Hello,
>>>
>>> I'd like to file a feature request for the bonding driver. Currently,
>>> there is no way for userspace to know whether the driver actually gets
>>> a MAC address. This results in the fact that dhcpcd sends MAC-less DHCP
>>> packets through bonding device if it is started before bond gets any
>>> slaves.
>>
>> A similar subject, involving bridge instead of bonding, was discussed a
>> few weeks ago in this thread:
>> http://marc.info/?l=linux-netdev&m=129939017116310&w=2
>>
>> In particular, I suggested to apply Stephen's suggestion not only to bridge but also to bonding.
>>
>> (http://marc.info/?l=linux-netdev&m=129948385024680&w=2)
>>
>> A bonding device should not report link up to userspace until at least one slave is present and up.
>>
>> And possibly, a bonding device should report link down if all slaves are down or all slave were removed.
>>
>> Jay, Andy, does this sounds sensible to you?
>
> 	I was just reading their bug and doing an experiment; I don't
> see that bonding reports carrier up until there's at least one slave
> (even if it's configured up), e.g.,
>
> # modprobe bonding
> # ifconfig bond0 up
> # cat /sys/class/net/bond0/carrier
> 0
> # echo +eth5>  /sys/class/net/bond0/bonding/slaves
> # cat /sys/class/net/bond0/carrier
> 1
>
> 	If there's a slave, there's a MAC assigned, since bond_enslave
> sets the master's MAC before it calls bond_set_carrier.
>
> 	In bond_create, as soon as register_netdevice returns, we call
> netif_carrier_off, and it stays off until bond_enslave runs
> successfully.

Agreed.

> 	Is there some race window there between the register and the
> netif_carrier_off?

It might be that dhcpd does not wait for link to be up before starting to send DHCP requests.

	Nicolas.
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