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SubjectRe: [PATCH v2] dynamic_debug: allow to work if debugfs is disabled
On Wed, Jan 22, 2020 at 01:56:48PM -0500, Jason Baron wrote:
>
>
> On 1/22/20 8:53 AM, 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, 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.
> >
>
> Hi Greg,
>
> Thanks for updating this. Just a comment below.
>
>
> > Reported-by: many different companies
> > Cc: Jason Baron <jbaron@akamai.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > v2: Fix up octal permissions and add procfs reference to the Kconfig
> > entry, thanks to Will for the review.
> >
> > .../admin-guide/dynamic-debug-howto.rst | 3 +++
> > lib/Kconfig.debug | 7 ++++---
> > lib/dynamic_debug.c | 17 ++++++++++++++---
> > 3 files changed, 21 insertions(+), 6 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..49980eb8c18e 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 not
> > @@ -116,8 +116,9 @@ config DYNAMIC_DEBUG
> > Usage:
> >
> > Dynamic debugging is controlled via the 'dynamic_debug/control' file,
> > - which is contained in the 'debugfs' filesystem. Thus, the debugfs
> > - filesystem must first be mounted before making use of this feature.
> > + which is contained in the 'debugfs' filesystem or procfs if
> > + debugfs is not present. Thus, the debugfs or procfs filesystem
> > + must first be mounted before making use of this feature.
> > We refer the control file as: <debugfs>/dynamic_debug/control. This
> > file contains a list of the debug statements that can be enabled. The
> > format for each line of the file is:
> > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> > index c60409138e13..0f1b26f10fb2 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)
> > {
>
> The naming now is a little confusing - dynamic_debug_init_control ?

Ah, good point. I'll go fix that up, and fix up the foolish build
warning that I missed...

thanks,

greg k-h

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