[ltt-dev] Updated TODO list before releasing LTTng bufferingtoLKML

[Zhaolei]

* Mathieu Desnoyers wrote:
>* Zhaolei (zhaolei at cn.fujitsu.com) wrote:
>> * Mathieu Desnoyers wrote:
>> >> > - move ltt/ltt-marker-control.c /proc interface to debugfs
>> >> >  I think we should integrate its directory tree to the new LTTng tracer
>> >> >  debugfs API like this :
>> >> > 
>> >> >  /debugfs/ltt/events/buffer_name/marker_name/
>> >> >    where we find files like :
>> >> >    state
>> >> >      write : 1/0 (on/off)
>> >> >      read  : 1/0 (on/off)
>> >> >    format
>> >> >      read : marker format string
>> >> Hello, Mathieu,
>> >> 
>> >> So we need to create a marker's debugfs-directory when user insmod
>> >>  a module with markers.
>> >> But i think we don't have a callback when user insmod, and we
>> >>  should avoid to patch kernel/module.c for this kind of function.
>> >> 
>> >> So, maybe we can only "echo marker_name 0/1" > marker-control.
>> >> Dou you have suggestion for me?
>> >> 
>> > 
>> > 
>> > Yes, we do have a callback in insmod.
>> > 
>> > See :
>> > 
>> > load_module()
>> > 
>> > #ifdef CONFIG_MARKERS
>> >        if (!mod->taints)
>> >                marker_update_probe_range(mod->markers,
>> >                        mod->markers + mod->num_markers);
>> > #endif
>> > 
>> > We would probably also have to get a callback in free_module to remove
>> > the marker directory entry when the last marker reference is gone. The
>> > same
>> > 
>> > #ifdef CONFIG_MARKERS
>> >        if (!mod->taints)
>> >                marker_update_probe_range(mod->markers,
>> >                        mod->markers + mod->num_markers);
>> > #endif
>> > 
>> > Could probably be used in free_module.
>> > 
>> Do you means we insert another callback as markers do?
>> as example in insmod:
>> #ifdef CONFIG_MARKERS
>>     if (!mod->taints)
>>         marker_update_probe_range(mod->markers,
>>          mod->markers + mod->num_markers);
>> #endif
>> #ifdef CONFIG_LTT
>>     if (!mod->taints)
>>         lttctl_create_dirs(mod->markers,
>>         mod->markers + mod->num_markers);
>> #endif
>> 
>> It it is true, i think because ltt_control will be a kernel module, and we can't
>> call a module's function in load_module().
>> 
>> So, maybe we can do as following:
>> 1: make module.c support callbackset.
>>   add following functions to module.c
>>   module_register_callback(enum MODULE_CALLBACK_TYPE type, callback_func func);
>>   module_unregister_callback(LOAD_MODULE, callback_func func);
>> 
>> 2: make marks and ltt_control use new function
>>   example if ltt_control's
>>   init() {module_register_callback(LOAD_MODULE, create_debugfs_dir);}
>>   exit() {module_unregister_callback(LOAD_MODULE, free_debugfs_dir);}
>>   void create_debugfs_dir(struct module *mod) {
>>     for (i = 0; i < mod->num_markers; i++ )
>>         ...
>>     }
>> 
> 
> No, no...
> 
> only marker_update_probe_range() needs to be called form module.c, at
> load_module() and exit_module().
> 
> It will add a marker entry to the hash table when necessary, and
> increment/decrement the reference count of this marker entry. The marker
> entry can be removed from the hash table when the refcount falls to 0
> and no probe is registered on the marker.
> 
> At the same time the marker entry is added to the hash table, a
> debugfs mkdir is done. When the entry is removed from the hash table, a
> debugfs rmdir is done.
> 
> Is it a bit more clear ?
Hi, Mathieu

I see.
But IMHO, markers is used by lttng, but is not part of lttng.
So, i think source for create files in /debugfs/ltt/... should not be placed in
markers.c.

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