linux-kernel - Re: [PATCH v2 20/24] dyndbg: WIP towards debug-print-class based callsite controls

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Date:   Wed, 17 Jun 2020 11:52:55 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Joe Perches <joe@...ches.com>, Jim Cromie <jim.cromie@...il.com>,
        jbaron@...mai.com, linux-kernel@...r.kernel.org,
        akpm@...uxfoundation.org, gregkh@...uxfoundation.org,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v2 20/24] dyndbg: WIP towards debug-print-class based
 callsite controls

On Wed 2020-06-17 10:31:54, Daniel Thompson wrote:
> On Tue, Jun 16, 2020 at 02:05:27PM -0700, Joe Perches wrote:
> > On Tue, 2020-06-16 at 15:45 +0200, Petr Mladek wrote:
> > > On Sat 2020-06-13 09:57:34, Jim Cromie wrote:
> > > > There are *lots* of ad-hoc debug printing solutions in kernel,
> > > > this is a 1st attempt at providing a common mechanism for many of them.
> > > 
> > > I agree that it might make sense to provide some common mechanism.
> > []
> > > My problem with this approach is that it is too generic. Each class
> > > would have different meaning in each subsystem.
> > > 
> > > It might help to replace any existing variants. But it would be hard
> > > for developers debugging the code. They would need to study/remember
> > > the meaning of these groups for particular subsystems. They would
> > > need to set different values for different messages.
> > > 
> > > Could you please provide more details about the potential users?
> > > Would be possible to find some common patterns and common
> > > meaning of the groups?
> > 
> > I doubt the utility of common patterns.
> > Verbosity is common but groupings are not.
> > 
> > Look at the DRM patterns vs other groups.
> 
> I've seen drm.debug mentioned a couple of times but the comments about
> it seem to only learn part of what is shows us.
> 
> drm.debug is a form of common grouping but it acts at a sub-system level
> rather then whole system (and gives a whole sub-system enable/disable).
> This is where grouping makes most sense.
> 
> The result is that drm.debug is easy to document, both in official
> kernel docs and in other resources (like the arch distro documentation).
> Having controls that are easy to document makes them easy to find and
> thus sub-system grouping leads directly to higher quality bug reports.

Thanks a lot for explanation.

Now, could anyone please tell me how this new dynamic debug feature
would allow to replace drm.debug option?

I mean what steps/commands will be needed instead of, for example
drm.debug=0x3 command line option?

Best Regards,
Petr