Subject: Re: Netlink API for bonding ?

From: Nicolas de Pesloüan<[email-masked]>
Date: Fri, 18 Sep 2009 00:10:55 +0200

Stephen Hemminger wrote:
> On Thu, 17 Sep 2009 23:44:30 +0200
> Nicolas de Pesloüan <[email-masked]> wrote:
> 
>> Stephen Hemminger wrote:
>>> On Mon, 31 Aug 2009 22:34:50 +0200
>>> Nicolas de Pesloüan <[email-masked]> wrote:
>>>
>>>> Stephen,
>>>>
>>>> Can you please describe the netlink API you plan to implement for bonding ?
>>>>
>>>> Both Jiri Pirko and I plan to add some advanced active slave selection rules, 
>>>> for more-than-two-slaves bonding configuration.
>>>>
>>>> Jay suggested that such advanced features be implemented in user space, using 
>>>> netlink to notify a daemon when slaves come up or fall down. I agree with Jay, 
>>>> but don't want to design something without having first a view at your proposed 
>>>> API for bonding.
>>>>
>>>> Do you plan to have some notification to user space, or only the ability to read 
>>>> and set bonding configuration using netlink ?
>>>>
>>>> Thanks,
>>>>
>>>> 	Nicolas.
>>> No paper spec, but was looking to add interface similar to vlan and macvlan.
>>> Just use (and extend if needed) existing rtnl_link_ops.
>>>
>>>
>>> Was not planning on adding a notification interface, thats good idea but
>>> really not what I was looking at.
>> What kind of notification system would you suggest to notify userland that a 
>> given bond device just lose the current active slave ?
> 
> First why should user land care?  Unless all slaves are gone maybe it
> should just be transparent.

Because we try to design a notification from kernel to userland when current 
active slave fail, to give an opportunity to userland to decide which non-failed 
slave should become the new active one. This is in order to try and move complex 
decisions to userland, only keeping very simple "two slaves" decisions into the 
kernel.

Think of it as the bonding counter part of moving STP to userland for bridge. 
Userland should be able to decide which slave should be the active one for the 
same reasons userland is able to decide which bridge port should be forwarding 
and which should be blocked.

I assume that we cannot just try to make the current bridge userland 
notification system more generic. May be I'm wrong. May be the ability to notify 
port failure, port coming back and BPDU for bridge is a superset of what we need 
to notify port failure and port coming back for bonding.

> Use existing link ops mechanism (see vlan and macvlan). You may need
> to add new operations, but these should be generic enough so that bonding and bridging
> have same operations. 
> 
>      .newlink => create bond device
>      .dellink => remove bond device
>      .newport => add slave
>      .delport => remove slave
> 
> Also, dellink should always work (even if slaves are present).

This sounds perfect for setup, but might not be good the elect the "best" port 
(active slave). Also, I assume a new RTNETLINK operation needs to be added for 
that. I thought that this was what you were working on. Do I miss something ? 
Does brctl use RTNETLINK for port setup ? Or do you plan to use iproute2 to 
replace brctl in the futur ?

> The terminology slave is not widely used outside of bonding, and so probably
> shouldn't be buried in the API.

Yes, you are definitely right with this point.

	Nicolas.