netdev - Re: [patch net-next v6 06/11] net: sched: use block index as a handle instead of qdisc when block is shared

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Date:   Sun, 7 Jan 2018 09:51:32 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        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, dsahern@...il.com
Subject: Re: [patch net-next v6 06/11] net: sched: use block index as a handle
 instead of qdisc when block is shared

On 18-01-07 09:28 AM, Jamal Hadi Salim wrote:
> On 18-01-07 08:46 AM, Jiri Pirko wrote:
>> Sun, Jan 07, 2018 at 02:11:19PM CET, jhs@...atatu.com wrote:
>>> On 18-01-06 03:43 PM, Jiri Pirko wrote:
>>>
>>>
>>>>
>>>>> @@ -886,8 +887,13 @@ static int tcf_fill_node(struct net *net, 
>>>>> struct sk_buff *skb,
>>>>>     tcm->tcm_family = AF_UNSPEC;
>>>>>     tcm->tcm__pad1 = 0;
>>>>>     tcm->tcm__pad2 = 0;
>>>>> -    tcm->tcm_ifindex = qdisc_dev(q)->ifindex;
>>>>> -    tcm->tcm_parent = parent;
>>>>> +    if (q) {
>>>>> +        tcm->tcm_ifindex = qdisc_dev(q)->ifindex;
>>>>> +        tcm->tcm_parent = parent;
>>>>> +    } else {
>>>>> +        tcm->tcm_ifindex = 0; /* block index is stored in parent */
>>>>> +        tcm->tcm_parent = block->index;
>>>>> +    }
>>>>
>>>> Please guys, please look at this reuse (also on clt side). I would like
>>>> you to double-check this reuse of existing API for balock_index 
>>>> carrying
>>>> purpose. I believe it's UAPI safe. But please, check it out carefully.
>>>>
>>>
>>>
>>> Should not break any ABI/UAPI AFAIK. Maybe go for a negative ifindex
>>> (not sure if zero means something speacial to someone).
>>
>> Like -1 means parent is block_index?
>>
> 
> Yes.
> 
>> Why would 0 mean something special? Could you point to a code that
>> suggests it?
>>
> 
> I cant point to any such code, it is just the ifindex is an int.
> And the negative space looks like less likely someone would think
> of using for signalling (0xFFFFFFFF as an example).
> tcpdump -i any probably assumes soem weird ifindex (havent looked
> at the code).
> 
> In any case, 0 is fine too.

Also a #define for whatever value you use would make it more readable,
ex:
#define IFINDEX_ANY ..

cheers,
jamal