Messages in this thread Patch in this message | | | Date | Fri, 7 May 2010 10:39:01 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH 2/9 - v2][RFC] tracing: Let tracepoints have data?passed to tracepoint callbacks |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > > > "Frederic Weisbecker" <fweisbec@gmail.com> wrote: > > >On Mon, May 03, 2010 at 11:40:47PM -0400, Steven Rostedt wrote: [...] > >> > >> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > >> index 78b4bd3..ee8059a 100644 > >> --- a/include/linux/tracepoint.h > >> +++ b/include/linux/tracepoint.h > >> @@ -20,12 +20,17 @@ > >> struct module; > >> struct tracepoint; > >> > >> +struct tracepoint_func { > >> + void *func; > >> + void *data; > >> +}; > >> + > >> struct tracepoint { > >> const char *name; /* Tracepoint name */ > >> int state; /* State. */ > >> void (*regfunc)(void); > >> void (*unregfunc)(void); > >> - void **funcs; > >> + struct tracepoint_func *funcs; > >> } __attribute__((aligned(32))); /* > >> * Aligned on 32 bytes because it is > >> * globally visible and gcc happily > >> @@ -46,14 +51,18 @@ struct tracepoint { > >> */ > >> #define __DO_TRACE(tp, proto, args) \ > >> do { \ > >> - void **it_func; \ > >> + struct tracepoint_func *it_func_ptr; \ > >> + void *it_func; \ > >> + void *__data; \ > >> \ > >> rcu_read_lock_sched_notrace(); \ > >> - it_func = rcu_dereference_sched((tp)->funcs); \ > >> - if (it_func) { \ > >> + it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > >> + if (it_func_ptr) { \ > >> do { \ > >> - ((void(*)(proto))(*it_func))(args); \ > >> - } while (*(++it_func)); \ > >> + it_func = (it_func_ptr)->func; \ > >> + __data = (it_func_ptr)->data; \ > >> + ((void(*)(proto))(it_func))(args); \ > > > > > >So, we had a talk about this and we concluded that it is probably fine > >on every archs to push one more argument than needed in a function. > > > > Yeah, I'm hoping it's fine.
How about changing the callback prototypes to match the call arguments (changing the type expected in register/unregister_trace, as well as an additional "check type" that I proposed for Ftrace) ?
Otherwise, you basically expect here that:
void fct(void *foo, void *bar, etc etc) (N parameters expected) {
}
called by:
fct(foo, bar, etc etc, foobar) (N + 1 parameters)
will always work.
Can you show me where the C standard says it is safe to do so ?
Thanks,
Mathieu
> > >But I think it would be nice to add a comment about this. Firstly > >because this line breaks all the self-explanation of the code, I mean > >I tried hard to find how the non-data callback case was handled :) > >Secondly to also to avoid people asking what happens here. > > > > OK I'll add a bit of comments to the macros. So much for my job security ;-) > > > > > > > > >> + } while ((++it_func_ptr)->func); \ > >> } \ > >> rcu_read_unlock_sched_notrace(); \ > >> } while (0) > >> @@ -63,23 +72,47 @@ 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(name, proto, args, data_proto, data_args) \ > >> extern struct tracepoint __tracepoint_##name; \ > >> static inline void trace_##name(proto) \ > >> { \ > >> if (unlikely(__tracepoint_##name.state)) \ > >> __DO_TRACE(&__tracepoint_##name, \ > >> - TP_PROTO(proto), TP_ARGS(args)); \ > >> + TP_PROTO(data_proto), \ > >> + TP_ARGS(data_args)); \ > >> } \ > >> static inline int register_trace_##name(void (*probe)(proto)) \ > >> { \ > >> - return tracepoint_probe_register(#name, (void *)probe); \ > >> + return tracepoint_probe_register(#name, (void *)probe, \ > >> + NULL); \ > >> + } \ > >> + static inline int unregister_trace_##name(void (*probe)(proto)) \ > >> + { \ > >> + return tracepoint_probe_unregister(#name, (void *)probe,\ > >> + NULL); \ > >> } \ > >> - static inline int unregister_trace_##name(void (*probe)(proto)) \ > >> + static inline int \ > >> + register_trace_##name##_data(void (*probe)(data_proto), \ > >> + void *data) \ > >> { \ > >> - return tracepoint_probe_unregister(#name, (void *)probe);\ > >> + return tracepoint_probe_register(#name, (void *)probe, \ > >> + data); \ > >> + } \ > >> + static inline int \ > >> + unregister_trace_##name##_data(void (*probe)(data_proto), \ > >> + void *data) \ > >> + { \ > >> + return tracepoint_probe_unregister(#name, (void *)probe,\ > >> + data); \ > >> } > >> > >> +#define DECLARE_TRACE_NOARGS(name) \ > >> + __DECLARE_TRACE(name, void, , void *__data, __data) > > > > > > > >That too, may be, deserves a small comment :) > > OK > > > > > > > > >> + > >> +#define DECLARE_TRACE(name, proto, args) \ > >> + __DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), \ > >> + PARAMS(proto, void *__data), \ > >> + PARAMS(args, __data)) > >> > >> #define DEFINE_TRACE_FN(name, reg, unreg) \ > >> static const char __tpstrtab_##name[] \ > >> @@ -100,19 +133,37 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin, > >> struct tracepoint *end); > >> [...]
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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