Subject: Re: [PATCH 1/4 net-next] net: phy: add Generic Netlink Ethernet switch configuration API

From: Jamal Hadi Salim <[email-masked]>
Date: Wed, 23 Oct 2013 10:09:50 -0400

On 10/23/13 09:31, Felix Fietkau wrote:
> On 2013-10-23 2:53 PM, Jamal Hadi Salim wrote:

> So you would like to have 'dummy' netdevs that don't actually work like
> real ones, just to get stats?

Not just stats, but other utilities, example:
*operational status read and admin status control,
*MAC address setting?
*MTU setting
* If something shows up on the cpu port and comes up, we can make it 
appear to be from such a netdev (for the case where this applies)
* etc

> Many of these switches are designed to work completely standalone, i.e.
> they receive their configuration once and then do their thing, often
> they don't even have special treatment for the CPU port.
>

So if i understood the worst case scenario:
- no packets will ever come to the CPU
- minimal config only such as configuring ports and what vlans they
accept
- you cant query the device for anything else not even stats

>> Can you at least retrieve the fdb? example how to figure out which
>> port a specific MAC address resides?
> On some of them, but not all.
>

I think this would be a fit for netdev->features to set capabilities at
initialization.
So canSetfdb, canGetfdb, canDelfdb etc

>> can support more than one vlan without having multiple bridges. example:
>> bridgeA: link ports {swp0:vlan1, swp1:vlan2, swp0:vlan4}
>> bridgeB: link ports {swp0:vlan3, swp1:vlan4, swp1:vlan2}
> So even more dummy interfaces that serve no real purpose other than
> configuration?

Yes. It may sound rediculous(trademark for that owned by DaveM), but
given the returns that all other classical linux tools work, I think it
is worth it.
Disclaimer: I still think this part is acrobatic in nature i.e no good
one-to-one mapping

> Correct.

How do you deal with those situations today example when a packet
shows up in the cpu port and they require routing?
Do you have one monolithic switch netdev ?

>I still get the impression that the model you're describing is
> mostly incompatible with what we're trying to do, and comes at the cost
> of quite a bit of extra complexity and bloat, not just on the
> implementation side, but on the configuration side as well.

/Sigh
I understand it is a dilema especially when you have your model proven
already with users.
The danger is one-offs where certain tools only work with certain
instantiations of common features. From a usability perspective,
it would be nice to use iproute2, ifconfig etc on the switch/ports and
not learn another tool (or program the switch to a different API).

> It also seems to make it more difficult to support vendor specific
> features. I strongly doubt that the slight increase in consistency
> between different kinds of switches/bridges is worth all of these extra
> costs.

I am not privy to what specific vendor features exist that are out of
whack. But note:
We have ability to set capabilities (netdev->features is one, but you 
can add another netdev->field). Would it not make sense for the driver
  to set such capabilities and the generic code to turn on/off certain
things? Example turn on netdev->ops->fdb_add if the switch is capable
etc.

cheers,
jamal