linux-kernel - Re: [RFC 1/2] net-next: add a dma_desc element to struct skb_shared

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Date:   Fri, 21 Jul 2017 22:37:53 +0200
From:   Florian Westphal <fw@...len.de>
To:     John Crispin <john@...ozen.org>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC 1/2] net-next: add a dma_desc element to struct
 skb_shared_info

John Crispin <john@...ozen.org> wrote:
> When the flow offloading engine forwards a packet to the DMA it will send
> additional info to the sw path. this includes
> * physical switch port
> * internal flow hash - this is required to populate the correct flow table
> entry
> * ppe state - this indicates what state the PPEs internal table is in for
> the flow
> * the reason why the packet was forwarde - these are things like bind,
> unbind, timed out, ...
> 
> once the flow table offloading patches are ready and upstream, the netfilter
> layer will see the SKB and pass it o to the flow table offloading code,

If this is about conntrack offloading, then I prefer if this is done
without changing any core network structure.

What about adding a new conntrack extension to hold whatever info
you need, and then allocate a conntrack entry in the driver?

This would obviously need core changes in conntrack (such as allowing
calls into conntrack from drivers without hard module dependencies,
and a thorough check if this causes backwards problems (e.g.
right now a "-m conntrack" check in the raw table can only succeed for
packets from lo interface).

But I think that could be worked around, esp. if we assume that we
won't see such entries a lot (assuming sw is slowpath and hw handles
most packets).

Thanks,
Florian