enable dynamic debug - doubt

enable dynamic debug - doubt

[Muni Sekhar]

[ Please keep me in CC as I'm not subscribed to the list]

 Hello,

The behaviour of dynamic debug prints are controlled via writing to a
control file in the 'debugfs'
filesystem(<debugfs>/dynamic_debug/control).

Here I would like to know what order should the echo(for eg: echo -n
'module sdhci +p' > /sys/kernel/debug/dynamic_debug/control) be
applied in relation to the module load - before or after?


-- 
Thanks,
Sekhar

Re: enable dynamic debug - doubt

[Andy Shevchenko]

On Tue, Nov 17, 2015 at 2:40 PM, Muni Sekhar <munisekharrms@gmail.com> wrote:
> [ Please keep me in CC as I'm not subscribed to the list]
>
>  Hello,
>
> The behaviour of dynamic debug prints are controlled via writing to a
> control file in the 'debugfs'
> filesystem(<debugfs>/dynamic_debug/control).
>
> Here I would like to know what order should the echo(for eg: echo -n
> 'module sdhci +p' > /sys/kernel/debug/dynamic_debug/control) be
> applied in relation to the module load - before or after?

Just imagine how debugfs works. It has probes over the code where
*_dbg/debug() prints are used. Those special data structures are kept
in the specific part of the file / kernel. If there is no module, how
will kernel know that there is a portion of such data there?

-- 
With Best Regards,
Andy Shevchenko

Re: enable dynamic debug - doubt

[Peter Hurley]

On 11/17/2015 07:40 AM, Muni Sekhar wrote:
> [ Please keep me in CC as I'm not subscribed to the list]
> 
>  Hello,
> 
> The behaviour of dynamic debug prints are controlled via writing to a
> control file in the 'debugfs'
> filesystem(<debugfs>/dynamic_debug/control).

That's not the only method. You'll want to read
Documentation/dynamic-debug-howto.txt; specifically, "Debug Messages at
Module Initialization Time" for ways to enable dynamic debug messages at
module load time.

Regards,
Peter Hurley

> Here I would like to know what order should the echo(for eg: echo -n
> 'module sdhci +p' > /sys/kernel/debug/dynamic_debug/control) be
> applied in relation to the module load - before or after?

Re: enable dynamic debug - doubt

[Muni Sekhar]

On Thu, Nov 19, 2015 at 2:38 AM, Peter Hurley <peter@hurleysoftware.com> wrote:
>
> On 11/17/2015 07:40 AM, Muni Sekhar wrote:
> > [ Please keep me in CC as I'm not subscribed to the list]
> >
> >  Hello,
> >
> > The behaviour of dynamic debug prints are controlled via writing to a
> > control file in the 'debugfs'
> > filesystem(<debugfs>/dynamic_debug/control).
>
> That's not the only method. You'll want to read
> Documentation/dynamic-debug-howto.txt; specifically, "Debug Messages at
> Module Initialization Time" for ways to enable dynamic debug messages at
> module load time.
>
> Regards,
> Peter Hurley
>
> > Here I would like to know what order should the echo(for eg: echo -n
> > 'module sdhci +p' > /sys/kernel/debug/dynamic_debug/control) be
> > applied in relation to the module load - before or after?
>
>



I just glanced through the Documentation/dynamic-debug-howto.txt and
now I am able to enable "Debug Messages at Module Initialization
Time".

Thanks Peter & Andy for the clarification.


--
Thanks,
Sekhar