From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Will Deacon <will@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>,
linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH] dynamic_debug: allow to work if debugfs is disabled
Date: Wed, 22 Jan 2020 09:12:05 +0100 [thread overview]
Message-ID: <20200122081205.GA2227985@kroah.com> (raw)
In-Reply-To: <20200122080352.GA15354@willie-the-truck>
On Wed, Jan 22, 2020 at 08:03:53AM +0000, Will Deacon wrote:
> On Wed, Jan 22, 2020 at 08:43:43AM +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.
>
> Why is the dyndbg= command-line option not sufficient for these use-cases?
They want to enable things after booting, and changing the kernel
command line is not something you can do on many systems (i.e.
locked-down-bootloaders like embedded systems).
Also, the whole option is prevented to be booted if debugfs is not
enabled, so the command line wouldn't even work in that situation :)
> > 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.
>
> Hmm. If something called "dynamic_debug" is getting moved out of debugfs,
> this does raise the question as to what (if anything) should be left behind.
> I worry this is a bit of a slippery slope...
I totally agree, but dynamic_debug is independant of debugfs with the
exception of the control file itself.
> > Reported-by: many different companies
> > Cc: Jason Baron <jbaron@akamai.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > .../admin-guide/dynamic-debug-howto.rst | 3 +++
> > lib/Kconfig.debug | 2 +-
> > lib/dynamic_debug.c | 17 ++++++++++++++---
> > 3 files changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
> > index 252e5ef324e5..41f43a373a6a 100644
> > --- a/Documentation/admin-guide/dynamic-debug-howto.rst
> > +++ b/Documentation/admin-guide/dynamic-debug-howto.rst
> > @@ -54,6 +54,9 @@ If you make a mistake with the syntax, the write will fail thus::
> > <debugfs>/dynamic_debug/control
> > -bash: echo: write error: Invalid argument
> >
> > +Note, for systems without 'debugfs' enabled, the control file can be
> > +also found in ``/proc/dynamic_debug/control``.
> > +
> > Viewing Dynamic Debug Behaviour
> > ===============================
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 5ffe144c9794..01d4add8b963 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -98,7 +98,7 @@ config DYNAMIC_DEBUG
> > bool "Enable dynamic printk() support"
> > default n
> > depends on PRINTK
> > - depends on DEBUG_FS
> > + depends on (DEBUG_FS || PROC_FS)
> > help
> >
> > Compiles debug level messages into the kernel, which would noti
>
> The help text here also needs updating, since it refers to debugfs.
Oops, missed that, thanks!
> > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> > index c60409138e13..077b2d6623ac 100644
> > --- a/lib/dynamic_debug.c
> > +++ b/lib/dynamic_debug.c
> > @@ -993,13 +993,24 @@ static __initdata int ddebug_init_success;
> >
> > static int __init dynamic_debug_init_debugfs(void)
> > {
> > - struct dentry *dir;
> > + struct dentry *debugfs_dir;
> > + struct proc_dir_entry *procfs_dir;
> >
> > if (!ddebug_init_success)
> > return -ENODEV;
> >
> > - dir = debugfs_create_dir("dynamic_debug", NULL);
> > - debugfs_create_file("control", 0644, dir, NULL, &ddebug_proc_fops);
> > + /* Create the control file in debugfs if it is enabled */
> > + if (debugfs_initialized) {
> > + debugfs_dir = debugfs_create_dir("dynamic_debug", NULL);
> > + debugfs_create_file("control", 0644, debugfs_dir, NULL,
> > + &ddebug_proc_fops);
> > + return 0;
> > + }
> > +
> > + /* No debugfs so put it in procfs instead */
> > + procfs_dir = proc_mkdir("dynamic_debug", NULL);
> > + if (procfs_dir)
> > + proc_create("control", 0x644, procfs_dir, &ddebug_proc_fops);
>
> Shouldn't this be octal rather than hex? Even then, I don't understand what
> use it is being able to read but not write to this file. Perhaps make it
> 0600 for /proc ?
Argh, my fault, fingers are used to typing hex.
You can read from the file to see what the current settings are, I was
just trying to mirror the debugfs permissions.
thanks,
greg k-h
next prev parent reply other threads:[~2020-01-22 8:12 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 7:43 [PATCH] dynamic_debug: allow to work if debugfs is disabled Greg Kroah-Hartman
2020-01-22 8:03 ` Will Deacon
2020-01-22 8:12 ` Greg Kroah-Hartman [this message]
2020-01-22 13:53 ` [PATCH v2] " Greg Kroah-Hartman
2020-01-22 18:56 ` Jason Baron
2020-01-22 19:29 ` Greg Kroah-Hartman
2020-01-22 19:31 ` [PATCH v3] " Greg Kroah-Hartman
2020-01-22 21:43 ` Randy Dunlap
2020-01-23 8:48 ` Greg Kroah-Hartman
2020-01-23 8:50 ` [PATCH v4] " Greg Kroah-Hartman
2020-01-23 9:36 ` Will Deacon
2020-01-23 15:53 ` [PATCH v3] " Theodore Y. Ts'o
2020-01-23 17:55 ` Greg Kroah-Hartman
2020-01-24 6:02 ` Theodore Y. Ts'o
2020-01-24 7:29 ` Greg Kroah-Hartman
2020-01-25 1:42 ` Theodore Y. Ts'o
2020-01-25 17:11 ` Jonathan Corbet
2020-01-27 22:19 ` Saravana Kannan
2020-02-09 11:05 ` [PATCH v5] " Greg Kroah-Hartman
2020-02-09 15:53 ` Joe Perches
2020-02-09 17:03 ` Greg Kroah-Hartman
2020-02-10 21:11 ` [PATCH v6] " Greg Kroah-Hartman
2020-02-10 21:15 ` Randy Dunlap
2020-02-12 21:58 ` Greg Kroah-Hartman
2020-02-11 11:01 ` Will Deacon
2020-01-25 0:03 ` [PATCH] " kbuild test robot
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