linux-kernel - Re: [PATCH v3] dynamic_debug: allow to work if debugfs is disabled

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Message-ID: <20200124060200.GG147870@mit.edu>
Date:   Fri, 24 Jan 2020 01:02:00 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jason Baron <jbaron@...mai.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3] dynamic_debug: allow to work if debugfs is disabled

On Thu, Jan 23, 2020 at 06:55:36PM +0100, Greg Kroah-Hartman wrote:
> > Instead of moving the control file IFF debugfs is enabled, what about
> > always making it available in /proc, and marking the control file for
> > dynamic_debug in debugfs as deprecated?  It would seem to me that this
> > would cause less confusion in the future....
> 
> Why deprecate it?  It's fine where it is, and most developer's have
> debugfs enabled so all is good.  I'd rather only use /proc as a
> last-resort.

This makes life difficult for scripts that manipulate the control
file, since they now need to check two different locations -- either
/sys/kernel/debug or /proc.  It's likely that people who normally use
distribution kernels where debugfs is disabled will have scripts which
are hard-coded to look in /proc, and then when they build a kernel
with debugfs enabled, the /proc entry will go **poof**, and their
script will break.

So regardless of what we do with the control file in debugfs, it might
be nice if moving forward, scripts can count on the /proc file
existing.

Cheers,

					- Ted