Re: [PATCH 18/25] dynamic_debug: Introduce global fake module param $module.dyndbg

[Jim Cromie]

On Thu, Dec 8, 2011 at 10:10 AM, Jason Baron <jbaron@xxxxxxxxxx> wrote:
> On Tue, Dec 06, 2011 at 12:11:28PM -0700, jim.cromie@xxxxxxxxx wrote:
>> From: Jim Cromie <jim.cromie@xxxxxxxxx>
>>
>> Rework Thomas Renninger's $module.ddebug boot-time debugging feature,
>> from https://lkml.org/lkml/2010/9/15/397
>>
>> Extend dynamic-debug facility to work during module initialization:
>>
>>   foo.dyndbg bar.dyndbg="$bar-query-string"
>>
>> This patch introduces a 'fake' module parameter: $module.ddebug for
>> all modules.  It is not explicitly added to each module, but is
>> implemented as an unknown-parameter callback invoked by kernel/param's
>> parse_one(), and it applies each module's query-string as if it were
>> written to the $DBGFS/dynamic_debug/control file.
>>
>> The module-name is added to the unknown-parameter callback signature
>> and to its caller: parse_one().  This lets the common callback know
>> what module its handling a common parameter for.
>>
>> If no value is given (as in foo.dyndbg example above), "+p" is
>> assumed, which enables all pr_debug callsites in the module.
>>
>> The parameter is not shown in /sys/module/*/parameters, thus it does
>> not use any resources.  Changes to the parameter are made via the
>> control file.
>>
>> Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
>> CC: Thomas Renninger <trenn@xxxxxxx>
>> CC: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
>> ---
>>  Documentation/dynamic-debug-howto.txt |   52 ++++++++++++++++++++++++++++++++-
>>  include/linux/dynamic_debug.h         |   11 +++++++
>>  include/linux/moduleparam.h           |    2 +-
>>  init/main.c                           |    7 ++--
>>  kernel/module.c                       |    3 +-
>>  kernel/params.c                       |   10 ++++--
>>  lib/dynamic_debug.c                   |   16 +++++++++-
>>  7 files changed, 89 insertions(+), 12 deletions(-)
>>
>> diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
>> index 989a892..56e496a 100644
>> --- a/Documentation/dynamic-debug-howto.txt
>> +++ b/Documentation/dynamic-debug-howto.txt
>> @@ -219,7 +219,7 @@ Note also that there is no convenient syntax to remove all
>>  the flags at once, you need to use "-flmpt".
>>
>>
>> -Debug messages during boot process
>> +Debug messages during Boot Process
>>  ==================================
>>
>>  To be able to activate debug messages during the boot process,
>> @@ -238,6 +238,45 @@ PCI (or other devices) initialization also is a hot candidate for using
>>  this boot parameter for debugging purposes.
>>
>>
>> +Debug Messages at Module Initialization Time
>> +============================================
>> +
>> +Enabling a module's debug messages via debug control file only works
>> +once the module is loaded; too late for callsites in init functions.
>> +And when module is unloaded, debug flag settings for the module are
>> +lost.  Instead, a "dyndbg" module parameter can be passed:
>> +
>> +     - via kernel boot parameter: (this form works on built-ins too)
>> +       module.dyndbg=+mfp
>> +       module.dyndbg # defaults to +p
>> +
>> +     - as an ordinary module parameter via modprobe
>> +       modprobe module dyndbg=+pmfl
>> +       modprobe module dyndbg # defaults to +p
>> +
>> +     - or the parameter can be used permanently via modprobe.conf(.local)
>> +       options module dyndbg=+pmflt
>> +       options module dyndbg # defaults to +p
>> +
>> +The $modname.dyndbg="value" should exclude "module $modname", as the
>> +$modname is taken from the param-name, and only 1 spec of each type is
>> +allowed.
>> +
>> +The dyndbg option is not implemented as an ordinary module parameter
>> +and thus will not show up in /sys/module/module_name/parameters/dyndbg
>> +The settings can be reverted later via the sysfs interface if the
>> +debug messages are no longer needed:
>> +
>> +      echo "module module_name -p" > <debugfs>/dynamic_debug/control
>> +
>> +$module.dyndbg="..." on boot-line works on built-in modules as well as
>> +those loaded by modprobe (from either early or normal userspace), and
>> +somewhat overlaps debug_query functionality.
>> +
>> +Modprobed modules get dyndbg flags given on boot-line after those
>> +given via modprobe (either explicitly, or from /etc/modprobe.d/*).
>> +This can surprise if boot-line arg subtracts flags.
>> +
>>  Examples
>>  ========
>>
>> @@ -264,3 +303,14 @@ nullarbor:~ # echo -n 'func svc_process -p' >
>>  // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
>>  nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
>>                               <debugfs>/dynamic_debug/control
>> +
>> +// boot-args example, with newlines and comments
>> +Kernel command line: ...
>> +  ddebug_query="func i2c_del_adapter +p; func tboot_probe +p"
>> +  dynamic_debug.verbose=1            // see whats going on
>> +  nouveau.dyndbg                     // implicit =+p
>> +  tsc_sync.dyndbg=+p                         // builtin on my kernel
>> +  i2c_core.dyndbg=+p                 // loaded by udev
>> +  *.dyndbg="=_"                              // wildcard applies to builtins
>> +  k10temp.dyndbg="+p # comment in query is stripped "
>> +  pnp.dyndbg="func pnpacpi_get_resources +p; func pnp_assign_mem +p" # multi
>
> I see you've added docs for the 'dyndbg' kernel command-line options,
> but then I don't see any changes in the code to 'unkown_bootoption'.
> What am I missing?
>
> Thanks,
>
> -Jason
>

Hmm.

I didnt make changes there cuz I didnt see any test case that
tripped up there.  All the $mod.dyndbg=... boot-args are picked
up by the load-module path.  IE I didnt see any that were missed.

Ive tested both built-in and loadable modules,
but may have missed the $mod.dyndbg (with default +p)
in the most recent revisions.
I'll retest everything, and make sure Ive covered all the corners.


/*
 * Unknown boot options get handed to init, unless they look like
 * unused parameters (modprobe will find them in /proc/cmdline).
 */

...

	/* Unused module parameter. */
	if (strchr(param, '.') && (!val || strchr(param, '.') < val))
		return 0;



BTW, I fixed a few checkpatch probs that crept in during revisions.
The only complaints that now remain are regarding
absolute paths in the howto, which are justified.
I dont want to spam the list, so held them back
pending more semantic issues (like this)

I'll report back on any missed use-cases.
Of course, if you see something specific missing, please say so.

thanks
Jim
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