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

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Date:   Fri, 13 Jan 2023 08:50:33 +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

Thu, Jan 12, 2023 at 08:58:58PM CET, leon@...nel.org wrote:
>On Thu, Jan 12, 2023 at 03:59:53PM +0100, Jiri Pirko wrote:
>> Thu, Jan 12, 2023 at 08:07:43AM CET, leon@...nel.org wrote:
>> >On Wed, Jan 11, 2023 at 01:29:03PM -0800, Jacob Keller wrote:
>> >> 
>> >> 
>> >> On 1/11/2023 8:45 AM, Jakub Kicinski wrote:
>> >> > On Wed, 11 Jan 2023 10:32:13 +0100 Jiri Pirko wrote:
>> >> >>>> I'm confused. You want to register objects after instance register?  
>> >> >>>
>> >> >>> +1, I think it's an anti-pattern.  
>> >> >>
>> >> >> Could you elaborate a bit please?
>> >> > 
>> >> > Mixing registering sub-objects before and after the instance is a bit
>> >> > of an anti-pattern. Easy to introduce bugs during reload and reset /
>> >> > error recovery. I thought that's what you were saying as well.
>> >> 
>> >> I was thinking of a case where an object is dynamic and might get added
>> >> based on events occurring after the devlink was registered.
>> >> 
>> >> But the more I think about it the less that makes sense. What events
>> >> would cause a whole subobject to be registerd which we wouldn't already
>> >> know about during initialization of devlink?
>> >> 
>> >> We do need some dynamic support because situations like "add port" will
>> >> add a port and then the ports subresources after the main devlink, but I
>> >> think that is already supported well and we'd add the port sub-resources
>> >> at the same time as the port.
>> >> 
>> >> But thinking more on this, there isn't really another good example since
>> >> we'd register things like health reporters, regions, resources, etc all
>> >> during initialization. Each of these sub objects may have dynamic
>> >> portions (ex: region captures, health events, etc) but the need for the
>> >> object should be known about during init time if its supported by the
>> >> device driver.
>> >
>> >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.
>> 
>> Yeah, but, we have reload. And during reload, instance is still
>> registered yet the subobject disappear and reappear. So that would be
>> inconsistent with the init/fini flow.
>> 
>> Perhaps during reload we should emulate complete fini/init notification
>> flow to the user?
>
>"reload" is triggered by me explicitly and I will get success/fail result
>at the end. There is no much meaning in subobject notifications during
>that operation.

Definitelly not. User would trigger reload, however another entity
(systemd for example) would listen to the notifications and react
if necessary.

>
>Thanks