Messages in this thread Patch in this message | | | Date | Wed, 22 Jan 2020 09:12:05 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH] dynamic_debug: allow to work if debugfs is disabled |
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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
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