Hello.

Right now it seems like the only interface
for registering the timer hooks is that one
of kernel/profile.c, and it is very limited.
The arch-specific timer hooks are provided
in an arch-specific headers as a static
functions.
Since my driver needs the timer hook, I
thought it might be a good idea to add an
API for registering the timer hooks.
The attached patch adds such an API and
converts all the relevant places to use it.
I changed oprofile to use it, and also
converted the arch-specific hooks, which
looks like a fair cleanup.

The API allows to register, unregister
and grab the timer hook. The grabbing
hook will always be executed first, and
can decide to prevent an execution of
the rest ones. The hook can have the
"run_always" flag set, in which case it
won't be bypassed, regardless of the
grabbing hook.

Does such an API look viable?
As usual, it is needed for the PC-Speaker
PCM driver that is currently in an ALSA CVS,
awaiting for the proper interface to appear
in the kernel.