netdev - Re: [net-next PATCH v3 00/12] Flow API

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Date:	Fri, 23 Jan 2015 16:25:56 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	John Fastabend <john.fastabend@...il.com>,
	simon.horman@...ronome.com, sfeldma@...il.com,
	netdev@...r.kernel.org, davem@...emloft.net, gerlitz.or@...il.com,
	andy@...yhouse.net, ast@...mgrid.com
Subject: Re: [net-next PATCH v3 00/12] Flow API

Fri, Jan 23, 2015 at 03:07:24PM CET, tgraf@...g.ch wrote:
>On 01/23/15 at 02:43pm, Jiri Pirko wrote:
>> Fri, Jan 23, 2015 at 01:28:38PM CET, tgraf@...g.ch wrote:
>> >If I understand this correctly then you propose to do the decision on
>> >whether to implement a flow in software or offload it to hardware in the
>> >xflows classifier and action. I had exactly the same architecture in mind
>> >initially when I first approached this and wanted to offload OVS
>> >datapath flows transparently to hardware.
>> 
>> Think about xflows as an iface to multiple backends, some sw and some hw.
>> User will be able to specify which backed he wants to use for particular
>> "commands".
>> 
>> So for example, ovs kernel datapath module will implement an xflows
>> backend and register it as "ovsdp". Rocker will implement another xflows
>> backend and register it as "rockerdp". Then, ovs userspace will use xflows
>> api to setup both backends independently, but using the same xflows api.
>> 
>> It is still up to userspace to decide what should be put where (what
>> backend to use).
>
>OK, sounds good so far. Although we can't completely ditch the existing
>genl based OVS flow API for obvious backwards compatibility reasons ;-)

Sure.

>
>How does John's API fit into this? How would you expose capabilities
>through xflows? How would it differ from what John proposes?

This certainly need more thinking. The capabilities could be exposed
either by separate a genl api (like in this version) or directly via TC
netlink iface (RTM_GETTFILTERCAP, RTM_GETACTIONCAP). The insides of the
message can stay the same. I like the second way better.

flow manipulation would happen as standard TC filters/actions manipulation.
Here, the Netlink messages could be also very similar to what John has now.


>
>Since this would be a regular tc classifier I assume it could be
>attached to any tc class and interface and then combined with other
>classifiers which OVS would not be aware of. How do you intend to
>resolve such conflicts?
>
>Example:
> eth0:
>   ingress qdisc:
>     cls prio 20 u32 match [...]
>     cls prio 10 xflows [...]
>
>If xflows offloads to hardware, the u32 classifier with higher
>priority is hidden unintentionally.


Right. We have to either introduce some limitations for xflows to
disallow this or let the user to take care of this. But it's similar
problem as if you use tc with John's API or ovs with John's API.
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