linux-kernel - Re: [PATCH v3 1/7] Documentation: dynamic-debug: Add description of level bitmask

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Date:   Tue, 09 Jun 2020 09:58:07 -0700
From:   Joe Perches <joe@...ches.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-acpi@...r.kernel.org,
        netdev@...r.kernel.org, Jason Baron <jbaron@...mai.com>,
        Jonathan Corbet <corbet@....net>,
        Jim Cromie <jim.cromie@...il.com>
Subject: Re: [PATCH v3 1/7] Documentation: dynamic-debug: Add description of
 level bitmask

On Tue, 2020-06-09 at 13:16 +0200, Greg Kroah-Hartman wrote:
> What is wrong with the existing control of dynamic
> debug messages that you want to add another type of arbitrary grouping
> to it? 

There is no existing grouping mechanism.

Many drivers and some subsystems used an internal one
before dynamic debug.

$ git grep "MODULE_PARM.*\bdebug\b"|wc -l
501

This is an attempt to unify those homebrew mechanisms.

Stanimir attempted to add one for his driver via a
driver specific standardized format substring for level.

> And who defines that grouping?

Individual driver authors

> Will it be driver/subsystem/arch/author specific?  Or kernel-wide?

driver specific

> This feels like it could easily get out of hand really quickly.

Likely not.  A question might be how useful all these
old debugging printks are today and if it's reasonable
to just delete them.

> Why not just use tracepoints if you really want to be fine-grained?

Weight and lack of class/group capability