[PATCH] markers: let marker_debug as module parameter

[PATCH] markers: let marker_debug as module parameter

[Lai Jiangshan]

if we want to enable marker debug output, we have to modify
the code and remake/reinstall the kernel in current code.

this patch enable marker_debug to be set when kernel start.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/marker.c b/kernel/marker.c
index 9f76c4a..5d8404f 100644
--- a/kernel/marker.c
+++ b/kernel/marker.c
@@ -28,8 +28,9 @@
 extern struct marker __start___markers[];
 extern struct marker __stop___markers[];
 
-/* Set to 1 to enable marker debug output */
-static const int marker_debug;
+static int marker_debug;
+module_param(marker_debug, bool, 0);
+MODULE_PARM_DESC(marker_debug, "Set to 1 to enable marker debug output");
 
 /*
  * markers_mutex nests inside module_mutex. Markers mutex protects the builtin

Re: [PATCH] markers: let marker_debug as module parameter

[Mathieu Desnoyers]

* Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
> 
> if we want to enable marker debug output, we have to modify
> the code and remake/reinstall the kernel in current code.
> 
> this patch enable marker_debug to be set when kernel start.
> 

Given it's only called at probe registration/unregistration and never
put in the critical path of an executed marker, it makes sense to make
this a kernel arg debug option. I like this patch :)

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/marker.c b/kernel/marker.c
> index 9f76c4a..5d8404f 100644
> --- a/kernel/marker.c
> +++ b/kernel/marker.c
> @@ -28,8 +28,9 @@
>  extern struct marker __start___markers[];
>  extern struct marker __stop___markers[];
>  
> -/* Set to 1 to enable marker debug output */
> -static const int marker_debug;
> +static int marker_debug;
> +module_param(marker_debug, bool, 0);
> +MODULE_PARM_DESC(marker_debug, "Set to 1 to enable marker debug output");
>  
>  /*
>   * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
> 
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Re: [PATCH] markers: let marker_debug as module parameter

[Ingo Molnar]

* Lai Jiangshan <laijs@cn.fujitsu.com> wrote:

> if we want to enable marker debug output, we have to modify
> the code and remake/reinstall the kernel in current code.
> 
> this patch enable marker_debug to be set when kernel start.
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/marker.c b/kernel/marker.c
> index 9f76c4a..5d8404f 100644
> --- a/kernel/marker.c
> +++ b/kernel/marker.c
> @@ -28,8 +28,9 @@
>  extern struct marker __start___markers[];
>  extern struct marker __stop___markers[];
>  
> -/* Set to 1 to enable marker debug output */
> -static const int marker_debug;
> +static int marker_debug;
> +module_param(marker_debug, bool, 0);
> +MODULE_PARM_DESC(marker_debug, "Set to 1 to enable marker debug output");

hm, in tip/master we already have ftrace_printk(), which allows such 
debug output to any of the active tracers. That is a far more useful way 
of debugging such things. See:

  http://people.redhat.com/mingo/tip.git/README

and:

  http://redhat.com/~mingo/sched-devel.git/readme-tracer.txt

note how much cleaner and more usable it will also become: no silly 
module flags or recompilation to activate this debug output, and no 
debug clutter in the syslog.

if you enable tracing in the 'nop' tracer then only the 
ftrace_printk()'s will be printed, no other trace entries.

	Ingo