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

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Date:   Fri, 15 Dec 2017 10:08:13 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        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, 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 5:46 PM, Jakub Kicinski wrote:
> On Wed, 13 Dec 2017 19:42:41 +0100, Jiri Pirko wrote:
>>>>>> 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.  
>>
>> I don't see why. The handle is the qdisc here.
> 
> If you look at it from Linux perspective that makes sense.  For people
> coming from switching world the fact that we use qdiscs as a handle for
> ACL blocks is an implementation detail..  is that the argument here?
> 

In a sense, yes. When configuring the filter, the primary command line
argument is the device. The qdisc is then derived from it and is an
implementation detail.