netdev - Re: [patch net-next v4 00/10] net: sched: allow qdiscs to share filter block instances

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Date:   Sat, 23 Dec 2017 19:54:47 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, jhs@...atatu.com, xiyou.wangcong@...il.com,
        mlxsw@...lanox.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        michael.chan@...adcom.com, ganeshgr@...lsio.com,
        saeedm@...lanox.com, matanb@...lanox.com, leonro@...lanox.com,
        idosch@...lanox.com, jakub.kicinski@...ronome.com,
        simon.horman@...ronome.com, pieter.jansenvanvuuren@...ronome.com,
        john.hurley@...ronome.com, alexander.h.duyck@...el.com,
        ogerlitz@...lanox.com, john.fastabend@...il.com,
        daniel@...earbox.net
Subject: Re: [patch net-next v4 00/10] net: sched: allow qdiscs to share
 filter block instances

On 12/23/17 9:54 AM, Jiri Pirko wrote:
> So back to the example. First, we create 2 qdiscs. Both will share
> block number 22. "22" is just an identification. If we don't pass any
> block number, a new one will be generated by kernel:
> 
> $ tc qdisc add dev ens7 ingress block 22
>                                 ^^^^^^^^
> $ tc qdisc add dev ens8 ingress block 22
>                                 ^^^^^^^^
> 
> Now if we list the qdiscs, we will see the block index in the output:
> 
> $ tc qdisc
> qdisc ingress ffff: dev ens7 parent ffff:fff1 block 22
> qdisc ingress ffff: dev ens8 parent ffff:fff1 block 22
> 
> To make is more visual, the situation looks like this:
> 
>    ens7 ingress qdisc                 ens7 ingress qdisc
>           |                                  |
>           |                                  |
>           +---------->  block 22  <----------+
> 
> Unlimited number of qdiscs may share the same block.
> 
> Now we can add filter to any of qdiscs sharing the same block:
> 
> $ tc filter add dev ens7 ingress protocol ip pref 25 flower dst_ip 192.168.0.0/16 action drop


Allowing config of a shared block through any qdisc that references it
is akin to me allowing nexthop objects to be manipulated by any route
that references it -- sure, it could be done but causes a lot surprises
to the user.

You are adding a new tc object -- a shared block. Why the resistance to
creating a proper API for managing it?