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

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Message-ID: <10227.1302893590@death>
Date:	Fri, 15 Apr 2011 11:53:10 -0700
From:	Jay Vosburgh <fubar@...ibm.com>
To:	=?UTF-8?B?Tmljb2xhcyBkZSBQZXNsb8O8YW4=?= 
	<nicolas.2p.debian@...il.com>
cc:	=?UTF-8?B?TWljaGHFgiBHw7Nybnk=?= 
	<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

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.

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

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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