linux-kernel - Re: [PATCH v4] dynamic_debug: allow to work if debugfs is disabled

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Date:   Thu, 23 Jan 2020 09:36:28 +0000
From:   Will Deacon <will@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jason Baron <jbaron@...mai.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4] dynamic_debug: allow to work if debugfs is disabled

On Thu, Jan 23, 2020 at 09:50:15AM +0100, Greg Kroah-Hartman wrote:
> With the realization that having debugfs enabled on "production" systems is
> generally not a good idea, debugfs is being disabled from more and more
> platforms over time.  However, the functionality of dynamic debugging still is
> needed at times, and since it relies on debugfs for its user api, having
> debugfs disabled also forces dynamic debug to be disabled.
> 
> To get around this, move the "control" file for dynamic_debug to procfs IFF
> debugfs is disabled.  This lets people turn on debugging as needed at runtime
> for individual driverfs and subsystems.
> 
> Reported-by: many different companies
> Cc: Jason Baron <jbaron@...mai.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> v4: tweaks to the .rst text thanks to Randy's review
> v3: rename init function as it is now no longer just for debugfs, thanks
>     to Jason for the review.
>     Fix build warning for debugfs_initialized call.
> v2: Fix up octal permissions and add procfs reference to the Kconfig
>     entry, thanks to Will for the review.
> 
>  .../admin-guide/dynamic-debug-howto.rst       |  3 +++
>  lib/Kconfig.debug                             |  7 ++++---
>  lib/dynamic_debug.c                           | 21 ++++++++++++++-----
>  3 files changed, 23 insertions(+), 8 deletions(-)

I had a brief "oh crap" moment when I thought you were exposing both the
procfs and debugfs interfaces at the same time, but thankfully that's not
the case. Whilst it's a bit of a shame that it's come to this, the code
looks pretty decent to me, so:

Acked-by: Will Deacon <will@...nel.org>

Thanks,

Will