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

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Date:   Thu, 12 Jan 2023 22:09:18 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        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 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.
> 
> 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