netdev - Re: [RFC PATCH 2/6] net/sched: flower: add support for matching on ConnTrack

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Date:   Mon, 28 Jan 2019 10:44:23 +0100
From:   Simon Horman <simon.horman@...ronome.com>
To:     Marcelo Ricardo Leitner <mleitner@...hat.com>
Cc:     Guy Shattah <sguy@...lanox.com>, Aaron Conole <aconole@...hat.com>,
        John Hurley <john.hurley@...ronome.com>,
        Justin Pettit <jpettit@....org>,
        Gregory Rose <gvrose8192@...il.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        Flavio Leitner <fbl@...hat.com>,
        Florian Westphal <fwestpha@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>, Rashid Khan <rkhan@...hat.com>,
        Sushil Kulkarni <sukulkar@...hat.com>,
        Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        Roi Dayan <roid@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Rony Efraim <ronye@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 2/6] net/sched: flower: add support for matching on
 ConnTrack

On Sat, Jan 26, 2019 at 01:52:01PM -0200, Marcelo Ricardo Leitner wrote:
> On Fri, Jan 25, 2019 at 02:37:13PM +0100, Simon Horman wrote:
> > Hi Marcelo,
> > 
> > On Fri, Jan 25, 2019 at 12:32:31AM -0200, Marcelo Ricardo Leitner wrote:
> > > Hook on flow dissector's new interface on ConnTrack from previous patch.
> > > 
> > > Signed-off-by: Marcelo Ricardo Leitner <mleitner@...hat.com>
> > > ---
> > >  include/uapi/linux/pkt_cls.h |  9 +++++++++
> > >  net/sched/cls_flower.c       | 33 +++++++++++++++++++++++++++++++++
> > >  2 files changed, 42 insertions(+)
> > > 
> > > diff --git a/include/uapi/linux/pkt_cls.h b/include/uapi/linux/pkt_cls.h
> > > index 95d0db2a8350dffb1dd20816591f3b179913fb2e..ba1f3bc01b2fdfd810e37a2b3853a1da1f838acf 100644
> > > --- a/include/uapi/linux/pkt_cls.h
> > > +++ b/include/uapi/linux/pkt_cls.h
> > > @@ -490,6 +490,15 @@ enum {
> > >  	TCA_FLOWER_KEY_PORT_DST_MIN,	/* be16 */
> > >  	TCA_FLOWER_KEY_PORT_DST_MAX,	/* be16 */
> > >  
> > > +	TCA_FLOWER_KEY_CT_ZONE,		/* u16 */
> > > +	TCA_FLOWER_KEY_CT_ZONE_MASK,	/* u16 */
> > > +	TCA_FLOWER_KEY_CT_STATE,	/* u8 */
> > > +	TCA_FLOWER_KEY_CT_STATE_MASK,	/* u8 */
> > 
> > With the corresponding flow dissector patch this API is
> > exposing the contents of an instance of enum ip_conntrack_info
> > as an ABI for conntrack state.
> > 
> > I believe (after getting similar review for my geneve options macthing
> > patches for flower) that this exposes implementation details as an ABI
> > to a degree that is not desirable.
> > 
> > My suggested would be to define, say in the form of named bits,
> > an ABI, that describes the state information that is exposed.
> > These bits may not correspond directly to the implementation of
> > ip_conntrack_info.
> > 
> > I think there should also be some consideration of if a mask makes
> > sense for the state as, f.e. in the implementation of enum
> > ip_conntrack_info not all bit combinations are valid. 
> 
> Right. ct_state must be handled differently. For conntrack it is a
> linear enum and as we want to be able to OR match, we will have to
> convert the states in a bitfield as you were saying or so.
> 
> I don't think the representation above wouldn't change, though: we have
> 8 bits wrapped under a u8. What would change is how we deal with it.
> 
> If iproute tc is able to parse the cmdline and set a corresponding bit
> for each state, the flower-side of flow dissector here should be
> mostly fine (need to consider the invalid bits as you mentioned, as
> part of sanity checking).
> Then just need to change on how flow dissector is reading ct_state
> from the packet.

I'm not entirely opposed to a KABI which defines bits of
TCA_FLOWER_KEY_CT_STATE in such a way that they match exactly
the current implementation of enum ip_conntrack_info (though I do suspect
that a better representation is possible, for some value of better).

But, on the other hand, I am not comfortable in simply sating that
TCA_FLOWER_KEY_CT_STATE is the same as enum ip_conntrack_info, because
that exposes an internal implementation detail which may change.

> Is your comment only related to ct_state or other fields too? I'm
> thinking only ct_state.

Sorry that I wasn't clear, I was only referring to ct_state.

> > > +	TCA_FLOWER_KEY_CT_MARK,		/* u32 */
> > > +	TCA_FLOWER_KEY_CT_MARK_MASK,	/* u32 */
> > > +	TCA_FLOWER_KEY_CT_LABEL,	/* 128 bits */
> > > +	TCA_FLOWER_KEY_CT_LABEL_MASK,	/* 128 bits */
> > > +
> > >  	__TCA_FLOWER_MAX,
> > >  };
> > 
> > ...
> >