netdev - Re: [patch net-next v3 00/10] net: sched: allow qdiscs to share filter block instances

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Message-ID: <3d3f57ae-23b7-6389-7276-3019f57dce01@gmail.com>
Date:   Wed, 13 Dec 2017 11:28:59 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, 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 v3 00/10] net: sched: allow qdiscs to share
 filter block instances

On 12/13/17 10:39 AM, Jiri Pirko wrote:
> Wed, Dec 13, 2017 at 06:18:04PM CET, dsahern@...il.com wrote:
>> On 12/13/17 10:07 AM, Jiri Pirko wrote:
>>> Wed, Dec 13, 2017 at 05:54:35PM CET, dsahern@...il.com wrote:
>>>> On 12/13/17 8:10 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
>>>>
>>>> I still say this is very odd user semantic - making changes to device M
>>>> and the changes magically affect device N. Operating on the shared block
>>>> as a separate object makes it is much more direct and clear.
>>>
>>> I plan to do it as a follow-up patch. But this is how things are done
>>> now and have to continue to work.
>>
>> Why is that? You are introducing the notion of a shared block with this
>> patch set. What is the legacy "how things are done now" you are
>> referring to?
> 
> Well, the filter add/del should just work no matter if the block behind is
> shared or not.

My argument is that modifying a shared block instance via a dev should
not be allowed. Those changes should only be allowed via the shared
block. So if a user puts adds a shared block to the device and then
attempts to add a filter via the device it should not be allowed.