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SubjectRe: [PATCH 3/7] add syscall tracepoints
On Fri, Jun 12, 2009 at 05:57:26PM -0400, Mathieu Desnoyers wrote:
> > Introduce a new 'DECLARE_TRACE_REG()' macro, so that tracepoints can associate
> > an external register/unregister function.
> >
> >
> > Signed-off-by: Jason Baron <jbaron@redhat.com>
> >
> > ---
> > include/linux/tracepoint.h | 27 +++++++++++++++++++++++----
> > 1 files changed, 23 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index 14df7e6..9a3660b 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -61,7 +61,7 @@ struct tracepoint {
> > * not add unwanted padding between the beginning of the section and the
> > * structure. Force alignment to the same alignment as the section start.
> > */
> > -#define DECLARE_TRACE(name, proto, args) \
> > +#define DECLARE_TRACE_REG(name, proto, args, reg, unreg) \
> > extern struct tracepoint __tracepoint_##name; \
> > static inline void trace_##name(proto) \
> > { \
> > @@ -71,13 +71,29 @@ struct tracepoint {
> > } \
> > static inline int register_trace_##name(void (*probe)(proto)) \
> > { \
> > - return tracepoint_probe_register(#name, (void *)probe); \
> > + int ret; \
> > + void (*func)(void) = (void (*)(void))reg; \
> > + \
> > + ret = tracepoint_probe_register(#name, (void *)probe); \
> > + if (func && !ret) \
> > + func(); \
>
> I don't see why you need to add this weird interface when all you really
> need to do is to call the function to set the TIF flags explicitly in
> reg_event_syscall_enter when registering a tracepoint.
>
> Mathieu
>

I could enable the TIF flag in reg_event_syscall_enter, however that
would not manage the TIF flag for other users of these traceoints. When
users 'register/unregister' with a tracepoint, they expect the tracepoint
to be enabled/disabled. If we move this functionality to the user, we are
changing how that interface works. Therefore, I associated the
enabling/disabling of the tracepoint, with the tracepoint definition.

thanks,

-Jason


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