[lttng-dev] How do you write an argument-less or payload-less kernel tracepoint?

[Mathieu Desnoyers]

----- Original Message -----
> From: "Daniel Thibault" <Daniel.Thibault at drdc-rddc.gc.ca>
> To: lttng-dev at lists.lttng.org
> Sent: Wednesday, February 12, 2014 4:54:55 PM
> Subject: [lttng-dev] How do you write an argument-less or payload-less	kernel tracepoint?
> 
> How do you write an argument-less kernel tracepoint?  I tried:
> 
> TRACE_EVENT(hello_nil,
>    TP_PROTO(),
>    TP_ARGS(),
> ...
> );
> 
> and
> 
> TRACE_EVENT_NOARGS(hello_nil,
> // TP_PROTO(int x),
> // TP_ARGS(x),
> ...
> );
> 
>    Without success.
> 
>    A payload-less tracepoint is possible, but causes a couple of warnings:
> 
> make[1]: entrant dans le répertoire « /usr/src/linux-headers-3.2.0-53-virtual
> »
>   CC [M]  /home/daniel/Documents/mymodule/hello.o
> In file included from include/trace/ftrace.h:356:0,
>                  from include/trace/define_trace.h:86,
>                  from include/trace/events/hello.h:151,
>                  from /home/daniel/Documents/mymodule/hello.c:5:
> include/trace/events/hello.h: In function 'ftrace_define_fields_hello_nil':
> include/trace/events/hello.h:130:1: attention : unused variable 'field'
> [-Wunused-variable]
> include/trace/events/hello.h:130:1: attention : 'ret' is used uninitialized
> in this function [-Wuninitialized]
>   Building modules, stage 2.
>   MODPOST 1 modules
>   LD [M]  /home/daniel/Documents/mymodule/hello.ko
> make[1]: quittant le répertoire « /usr/src/linux-headers-3.2.0-53-virtual »
> 
>    Is it possible to get rid of the warnings?

In lttng-modules, try:

TRACE_EVENT_NOARGS(hello_nil,
    TP_STRUCT__entry(),
    TP_fast_assign(),
    TP_printk()
)

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com