[ltt-dev] Updated TODO list before releasing LTTng bufferingto LKML

[compudj@krystal.dyndns.org (Mathieu Desnoyers)]

* 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 ?

Mathieu




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-- 
Mathieu Desnoyers
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