Re: [PATCH 0/3] tracing: introduce TRACE_EVENT_NONE and use it

From: Yafang Shao
Date: Mon Mar 25 2019 - 22:25:14 EST


On Tue, Mar 26, 2019 at 10:17 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Tue, 26 Mar 2019 09:40:04 +0800
> Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> > In this patchset, I introduce a new macro TRACE_EVENT_NONE(), which will
> > define a tracepoint as a do-nothing inline function.
> > #define TRACE_EVENT_NONE(name, proto) \
> > static inline void trace_##name(proto) \
> > { } \
> > static inline bool trace_##name##_enabled(void) \
> > { \
> > return false; \
> > }
> >
>
> BTW, I prefer a name of TRACE_EVENT_DISABLED()
>
> Which shows that it is disabled, or TRACE_EVENT_UNDEF(), or
> TRACE_EVENT_NOP(). Something that states it is turned off. When I first
> saw NONE() I thought it was another attempt to introduce zero parameter
> trace events.
>

I prefer TRACE_EVENT_NOP.
I will change it.

Thanks
Yafang

>
> > Let's take some example for why this macro is needed.
> >
> > - sched
> > The tracepoints trace_sched_stat_{iowait, blocked, wait, sleep} should
> > be not exposed to user if CONFIG_SCHEDSTATS is not set.
> > We can place #ifdef in the kernel/sched/fair.c to fix it, but we
> > don't want to sprinkle #ifdef.
>
> But you still sprinkle #ifdef in the header, but the part I don't like
> is the need to duplicate the prototypes and the like.
>
>
> > So with TRACE_EVENT_NONE(), we can fix it in
> > include/trace/events/sched.h.
> >
> > - rcu
> > When CONFIG_RCU_TRACE is not set, some rcu tracepoints are define as
> > do-nothing macro without validating arguments, that is not proper.
> > We should validate the arguments.
> >
> > Yafang Shao (3):
> > tracing: introduce TRACE_EVENT_NONE()
> > sched/fair: do not expose some tracepoints to user if
> > CONFIG_SCHEDSTATS is not set
> > rcu: validate arguments for rcu tracepoints
> >
>
> See my reply in the next patch.
>
> -- Steve