linux-kernel - Re: [PATCH v5] dynamic_debug: allow to work if debugfs is disabled

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Message-ID: <20200209170354.GA3171@kroah.com>
Date:   Sun, 9 Feb 2020 18:03:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Joe Perches <joe@...ches.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Jonathan Corbet <corbet@....net>,
        Saravana Kannan <saravanak@...gle.com>,
        Jason Baron <jbaron@...mai.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v5] dynamic_debug: allow to work if debugfs is disabled

On Sun, Feb 09, 2020 at 07:53:38AM -0800, Joe Perches wrote:
> On Sun, 2020-02-09 at 12:05 +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, also create the "control" file for dynamic_debug in
> > procfs.  This allows 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>
> > ---
> > v5: as many people asked for it, now enable the control file in both
> >     debugfs and procfs at the same time.
> 
> So now there can be differences in the two control files
> and these are readable files are sometimes parsed by
> scripts.

What difference will there be?  They should both be the same, as they
point to the identical fops behind the virtual file.

> It'd be better to figure out how to soft link the files.

A symlink is not going to work, but this should be fine from what I can
tell.  I'll do some more debugging tonight, but all was fine last I
tried this last week.

thanks,

greg k-h