netdev - Re: [PATCH net-next 7/9] devlink: allow registering parameters after the instance

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Date:   Thu, 12 Jan 2023 14:44:43 -0800
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Leon Romanovsky <leon@...nel.org>, Jakub Kicinski <kuba@...nel.org>
CC:     Jiri Pirko <jiri@...nulli.us>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <edumazet@...gle.com>,
        <pabeni@...hat.com>
Subject: Re: [PATCH net-next 7/9] devlink: allow registering parameters after
 the instance



On 1/12/2023 12:09 PM, Leon Romanovsky wrote:
> On Thu, Jan 12, 2023 at 11:20:21AM -0800, Jakub Kicinski wrote:
>> On Thu, 12 Jan 2023 09:07:43 +0200 Leon Romanovsky wrote:
>>> As a user, I don't want to see any late dynamic object addition which is
>>> not triggered by me explicitly. As it doesn't make any sense to add
>>> various delays per-vendor/kernel in configuration scripts just because
>>> not everything is ready. Users need predictability, lazy addition of
>>> objects adds chaos instead.
>>>
>>> Agree with Jakub, it is anti-pattern.
>>
>> To be clear my preference would be to always construct the three from
>> the root. Register the main instance, then sub-objects. I mean - you
>> tried forcing the opposite order and it only succeeded in 90-something
>> percent of cases. There's always special cases.
>>

Right. I think its easier to simply require devlink to be registered first.

>> I don't understand your concern about user experience here. We have
>> notifications for each sub-object. Plus I think drivers should hold 
>> the instance lock throughout the probe routine. I don't see a scenario
>> in which registering the main instance first would lead to retry/sleep
>> hacks in user space, do you? I'm talking about devlink and the subobjs
>> we have specifically.
> 
> The term "dynamic object addition" means for me what driver authors will
> be able to add objects anytime in lifetime of the driver. I'm pretty sure
> that once you allow that, we will see zoo here. Over time, you will get
> everything from .probe() to workqueues. The latter caused me to write
> about retry/sleep hacks.
> 
> If you success to force everyone to add objects in .probe() only, it
> will be very close to what I tried to achieve.
> 
> Thanks

Yea. I was initially thinking of something like that, but I've convinced
myself that its a bad idea. The only "dynamic" objects (added after the
initialization phase of devlink) should be those which are triggered via
user space request (i.e. "devlink port add").

Thanks,
Jake