Subject: Re: [SET 2][PATCH 2/8][bonding] Propagating master's settings to slaves

From: Shmulik Hen <[email-masked]>
Date: Mon, 11 Aug 2003 13:08:48 +0300

On Monday 11 August 2003 05:51 am, you wrote:
> On Sat, 2003-08-09 at 06:29, Hen, Shmulik wrote:
> > Not sure I fully understood the concerns above, but I'll try
> > to explain what the change was all about.
>
> I think it wasnt the one specific change rather a few posted that i
> spent a minute or two staring at. And you confirm my suspicion
> below.

I probably didn't make myself clear - by "understood" I wanted to say 
I probably didn't get the *meaning* of the whole sentence , and not 
"I don't under stand why you are concerned".
(English is not my native tongue :) ).

> I am not very familiar with the bonding code although i think you
> guys have been doing very good work since you got involved.
> In any case the approach you state above is wrong. Actually Stephen
> Hemminger and I discussed this for bridging. Post 2.6 he is going
> to remove a lot of the bridge policy (or "brain" as you call it)
> out of the kernel. Netlink for kernel<->userspace not /proc. I
> think we should head towards that direction so we can have more
> sophisticated management.

I, on the other hand, am not familiar with the bridging code and I 
don't know what it actually does internally, I just noticed that 
regarding config operations, most of the code is done at the kernel 
level as response to ioctl commands.

I'll try to clarify how that relates to bonding. The ifenslave utility 
has very little "brain" as it is, and all it knows how to do 
currently is enslave/release slave devices and change the current 
active slave. It also has some ability to extract status info from 
the bond and present it nicely for a user.

The "brain" I was referring to in the bonding module itself has to do 
with timer functions monitoring link status or Tx/Rx activity of the 
slaves, and once a faulty slave is detected, switch to use another 
one instead according to the teaming mode. There are no large scale 
decision making nor major CPU consuming computations that are part of 
the continuous operation of the module that is basically handle Rx/Tx 
on slaves.

The bonding module doesn't need to access any special info that is 
normally available to user space apps. What it does need is very 
short response time and accessibility to kernel internal resources 
like net devices info to make it a high availability intermediate 
driver.

Trying to move that from the kernel module into the config application 
seems to be a very hard task to implement since we'll have to find a 
way to make the application constantly aware to the specifics like 
current topology, slave-to-bond affiliation, updated status of each 
slave, etc., etc. It would also mean that the driver will have to 
wait for the application to tell it what to do each time it needs a 
decision, and by that we'll surely suffer some performance hit and 
probably get low availability or temporary loss of communications.

Going back to the first problem, discussions on the bonding 
development list pointed that it might be better if we moved the 
configuration-time decisions making to the driver, so the application 
wouldn't have to deal with situations like:
1) get the master's MTU settings, master's teaming mode, communication 
   version, backwards compatibility issues, etc.
2) figure if need to set MTU to slave according to all that,
3) try to set that on the new slave being added,
4) if not successfull, decide if may enslave anyway or,
5) maybe undo all previous settings already done to the slave 
   (needs a way to retrieve old values)
6) decide if should go on or fail any further operations
7) repeat the above for all other settings

On the other hand, what we want to get to is something more like:
1) tell bonding to add slave X to bond Y,
2) watch for error returns,
3) print a nice message according to the type of the error.

While the driver, already aware of all possible relevant data, makes 
all decisions, performs settings, handles compatibility issues, 
checks for failures at each stage, handles any undo steps, and return 
success/error values accordingly.

> Thoughts?

Mostly explanations :)

Is there anywhere I can see what you refereed to as discussions with 
Stephen Hemminger ? I would really like to know how and what could 
also be applied to bonding.

	Regards,
	Shmulik.