Messages in this thread | | | Date | Wed, 22 Jan 2020 08:03:53 +0000 | From | Will Deacon <> | Subject | Re: [PATCH] dynamic_debug: allow to work if debugfs is disabled |
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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?
> 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...
Anywho, comments below.
> 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.
> 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 ?
Will
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