netdev - Re: Deliver skbs to intermediate interfaces, when using cascaded rx-handlers

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Message-ID: <20140221171034.GA2488@localhost.localdomain>
Date:	Fri, 21 Feb 2014 14:10:35 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Tobias Waldekranz <tobias@...dekranz.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Deliver skbs to intermediate interfaces, when using cascaded
 rx-handlers

On Fri, Feb 21, 2014 at 11:01:58AM +0100, Tobias Waldekranz wrote:
> I have a system with the following configuration:
> 
>    * eth0 is a regular Ethernet MAC, connected to a hardware switch.
>    * port[1-4] are the in-kernel representation of the switch.
>    * team0 is a regular team-interface which bonds port1 and port2.
> 
>       +-------+
>       | team0 |
>       +---+---+
>           |
>      +----+----+
>      |         |
>  +---+---+ +---+---+ +-------+ +-------+
>  | port1 | | port2 | | port3 | | port4 | 
>  +---+---+ +---+---+ +---+---+ +---+---+
>      |         |         |         |
>      +---------+----+----+---------+
>                     |
>                 +---+---+
>                 | eth0  |
>                 +-------+
> 
> Both the switch and the team driver attaches rx-handlers to their
> lower layers. The problem is that team expects LACP frames that
> are intercepted by team0, to also be delivered to the port interface
> by __netif_receive_skb_core (in the final iteration of the registered
> protocols). However in this case, when two rx-handlers are cascaded,
> the skb will be delivered to eth0, since that is the original device
> (orig_dev).

Indeed. It is not possible to update orig_dev, so it is stuck
on eth0 regardless of all the stacked interfaces.

> There are a few ways this can be solved as far as i can see:
> 
>    1. Introduce a new rx-handler return code that specifies that
>    skb->dev has been altered, like RX_HANDLER_ANOTHER, and that we
>    also want to change orig_dev to this new device.

But then you need to know which rx-handler will run next, because
the orig_dev might still be implicit wanted.
 
>    2. Change the switch driver to return RX_HANDLER_CONSUMED and then
>    queue the skb all over again, though I am afraid that this will eat
>    some cycles.

Before queue again, you need to update skb->dev, right? This seems
similar to (1).

>    3. Keep track of all traversed interfaces and change the final
>    protocol iteration to deliver the skb to all intermediate devices.

That's what I thought too.

fbl
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