Messages in this thread | | | Date | Tue, 27 Apr 2010 17:08:29 +0800 | From | Li Zefan <> | Subject | Re: [PATCH 02/10][RFC] tracing: Let tracepoints have data passed to tracepoint callbacks |
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Steven Rostedt wrote: > From: Steven Rostedt <srostedt@redhat.com> > > This patch allows data to be passed to the tracepoint callbacks > if the tracepoint was created to do so. > > If a tracepoint is defined with: > > DECLARE_TRACE_DATA(name, proto, args) > > Then a registered function can also register data to be passed > to the tracepoint as such: > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > /* In the C file */ > > DEFINE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status)); > > [...] > > trace_mytacepoint(status); > > /* In a file registering this tracepoint */ > > int my_callback(int status, void *data) > { > struct my_struct my_data = data; > [...] > } > > [...] > my_data = kmalloc(sizeof(*my_data), GFP_KERNEL); > init_my_data(my_data); > register_trace_mytracepoint_data(my_callback, my_data); > > The same callback can also be registered to the same tracepoint as long > as the data registered is the same. Note, the data must also be used > to unregister the callback: > > unregister_trace_mytracepoint_data(my_callback, my_data); > > Because of the data parameter, tracepoints declared this way can not have > no args. That is: > > DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(void), TP_ARGS()); > > will cause an error, but the original DECLARE_TRACE still allows for this. > > The DECLARE_TRACE_DATA() will be used by TRACE_EVENT() so that it > can reuse code and bring the size of the tracepoint footprint down. > This means that TRACE_EVENT()s must have at least one argument defined.
We have to define at least on argument in TRACE_EVENT() even without this patch, otherwise it'll cause compile error while expanding the macros.
> This should not be a problem since we should never have a static > tracepoint in the kernel that simply says "Look I'm here!". >
We do have such a tracepoint. ;)
That is trace_power_end, and it uses a dummy argument merely for passing compilation.
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