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

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Date:   Fri, 13 Jan 2023 08:53:55 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        Jakub Kicinski <kuba@...nel.org>, 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

Fri, Jan 13, 2023 at 07:45:46AM CET, leon@...nel.org wrote:
>On Thu, Jan 12, 2023 at 02:44:43PM -0800, Jacob Keller wrote:
>> 
>> 
>> 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.
>
>Back then, we had only one special case - netdevsim. I still think that
>all recent complexity that was brought to the devlink could be avoided
>if we would change netdevsim to behave as HW driver (remove sysfs).
>
>> Right. I think its easier to simply require devlink to be registered first.
>
>devlink_register() is no more than a fancy way to say to the world: "I'm
>ready to accept commands". Right now, when the need_lock flag is removed
>from all devlink commands, we can place devlink_register() at any place.
>
>> 
>> >> 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").
>
>Exactly.

And reload as well.

>
>> 
>> Thanks,
>> Jake