netdev - Re: [PATCH v4 net-next 03/12] net-shapers: implement NL get operation

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Message-ID: <47cde674-9f24-4b14-a3d2-216904617c8f@redhat.com>
Date: Tue, 27 Aug 2024 09:36:14 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, Jiri Pirko <jiri@...nulli.us>,
 Madhu Chittim <madhu.chittim@...el.com>,
 Sridhar Samudrala <sridhar.samudrala@...el.com>,
 Simon Horman <horms@...nel.org>, John Fastabend <john.fastabend@...il.com>,
 Sunil Kovvuri Goutham <sgoutham@...vell.com>,
 Jamal Hadi Salim <jhs@...atatu.com>, Donald Hunter <donald.hunter@...il.com>
Subject: Re: [PATCH v4 net-next 03/12] net-shapers: implement NL get operation



On 8/27/24 03:55, Jakub Kicinski wrote:
> On Fri, 23 Aug 2024 10:52:04 +0200 Paolo Abeni wrote:
>>>> + * comprising the shaper scope and a scope-specific id.
>>>> + */
>>>> +struct net_shaper_ops {
>>>> +	/**
>>>> +	 * @group: create the specified shapers scheduling group
>>>> +	 *
>>>> +	 * Nest the @leaves shapers identified by @leaves_handles under the
>>>> +	 * @root shaper identified by @root_handle. All the shapers belong
>>>> +	 * to the network device @dev. The @leaves and @leaves_handles shaper
>>>> +	 * arrays size is specified by @leaves_count.
>>>> +	 * Create either the @leaves and the @root shaper; or if they already
>>>> +	 * exists, links them together in the desired way.
>>>> +	 * @leaves scope must be NET_SHAPER_SCOPE_QUEUE.
>>>
>>> Or SCOPE_NODE, no?
>>
>> I had a few back-and-forth between the two options, enforcing only QUEUE
>> leaves or allowing even NODE.
>>
>> I think the first option is general enough - can create arbitrary
>> topologies with the same amount of operations - and leads to slightly
>> simpler code, but no objections for allow both.
> 
> Ah, so we can only "grow the tree from the side of the leaves",
> so to speak? We can't create a group in the middle of the hierarchy?

With the posted code, we can't. It can be implemented, but I think it 
will make the interface confusing.

> I have no strong use for groups in between, maybe just mention in
> a comment or cover letter.

I'll do, thanks.



> 
>>>> +static int net_shaper_fill_handle(struct sk_buff *msg,
>>>> +				  const struct net_shaper_handle *handle,
>>>> +				  u32 type, const struct genl_info *info)
>>>> +{
>>>> +	struct nlattr *handle_attr;
>>>> +
>>>> +	if (handle->scope == NET_SHAPER_SCOPE_UNSPEC)
>>>> +		return 0;
>>>
>>> In what context can we try to fill handle with scope unspec?
>>
>> Uhmm... should happen only in buggy situation. What about adding adding
>> WARN_ON_ONCE() ?
> 
> That's better, at least it will express that it's not expected.

I added the WARN in my local build, and that reminded me the tree root 
(netdev) has UNSPEC parent. So I think we are better off with simply a 
comment there.

Thanks,

Paolo