netdev - Re: [RFC net-next] net: sch_clsact: add support for global per-netns classifier mode

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Date:   Tue, 5 Sep 2017 18:25:47 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [RFC net-next] net: sch_clsact: add support for global per-netns
 classifier mode

On 17-09-05 06:01 PM, Roopa Prabhu wrote:

> 
> yes, like Nikolay says we have been discussing this as well. Nikolay's
> patch is a cleaver and most importantly non-invasive
> way today given the anchor point for tc rules is a netdev. we have
> also considered a separate implicit tc anchor device.
>   lo seemed like a good fit for all global rules given it is already
> available. And it is not uncommon to hang off global
> network config on the loopback interface.
> 

IMO, Jiri has done all the necessary work already with the concept of
blocks. We dont really need the netdev to be the attachment point.

You can add to a block in many locations in the kernel by
constructing the proper "coordinates" in the tcmsg.
i.e this:
   tcmsg {
         unsigned char   tcm_family;
         unsigned char   tcm__pad1;
         unsigned short  tcm__pad2;
         int             tcm_ifindex;
         __u32           tcm_handle;
         __u32           tcm_parent;
}

If you were to set tcm_ifindex to -1 (since that is not a legit
ifindex) then all we need to do is define a parent for a
different location. Current locations tied to netdevs are:
-----
#define TC_H_ROOT       (0xFFFFFFFFU)
#define TC_H_INGRESS    (0xFFFFFFF1U)
#define TC_H_CLSACT     TC_H_INGRESS

#define TC_H_MIN_INGRESS        0xFFF2U
#define TC_H_MIN_EGRESS         0xFFF3U
-----

You should be able to say add a location which maps to a pre-routing
or post-routing etc; and this would work as well...

cheers,
jamal