Commit fea6ac55 authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

tracing: Add example and documentation for new __vstring() macro 

Update the sample trace events to include an example that uses the new
__vstring() helpers for TRACE_EVENTS.

Link: https://lkml.kernel.org/r/20220715175555.16375a3b@gandalf.local.home



Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent f5eab65f

samples/trace_events/trace-events-sample.c

+12 −2
Original line number Diff line number Diff line
@@ -19,9 +19,10 @@ static const char *random_strings[] = { 
	"One ring to rule them all"

};



static void simple_thread_func(int cnt)

static void do_simple_thread_func(int cnt, const char *fmt, ...)

{

	unsigned long bitmask[1] = {0xdeadbeefUL};

	va_list va;

	int array[6];

	int len = cnt % 5;

	int i;
@@ -33,9 +34,13 @@ static void simple_thread_func(int cnt) 
		array[i] = i + 1;

	array[i] = 0;



	va_start(va, fmt);



	/* Silly tracepoints */

	trace_foo_bar("hello", cnt, array, random_strings[len],

		      current->cpus_ptr);

		      current->cpus_ptr, fmt, &va);



	va_end(va);



	trace_foo_with_template_simple("HELLO", cnt);
@@ -48,6 +53,11 @@ static void simple_thread_func(int cnt) 
	trace_foo_rel_loc("Hello __rel_loc", cnt, bitmask);

}



static void simple_thread_func(int cnt)

{

	do_simple_thread_func(cnt, "iter=%d", cnt);

}



static int simple_thread(void *arg)

{

	int cnt = 0;

samples/trace_events/trace-events-sample.h

+28 −4
Original line number Diff line number Diff line
@@ -141,6 +141,27 @@ 
 *         In most cases, the __assign_str() macro will take the same

 *         parameters as the __string() macro had to declare the string.

 *

 *   __vstring: This is similar to __string() but instead of taking a

 *         dynamic length, it takes a variable list va_list 'va' variable.

 *         Some event callers already have a message from parameters saved

 *         in a va_list. Passing in the format and the va_list variable

 *         will save just enough on the ring buffer for that string.

 *         Note, the va variable used is a pointer to a va_list, not

 *         to the va_list directly.

 *

 *           (va_list *va)

 *

 *         __vstring(foo, fmt, va)  is similar to:  vsnprintf(foo, fmt, va)

 *

 *         To assign the string, use the helper macro __assign_vstr().

 *

 *         __assign_vstr(foo, fmt, va);

 *

 *         In most cases, the __assign_vstr() macro will take the same

 *         parameters as the __vstring() macro had to declare the string.

 *         Use __get_str() to retrieve the __vstring() just like it would for

 *         __string().

 *

 *   __string_len: This is a helper to a __dynamic_array, but it understands

 *	   that the array has characters in it, and with the combined

 *         use of __assign_str_len(), it will allocate 'len' + 1 bytes
@@ -256,9 +277,10 @@ TRACE_DEFINE_ENUM(TRACE_SAMPLE_ZOO); 
TRACE_EVENT(foo_bar,



	TP_PROTO(const char *foo, int bar, const int *lst,

		 const char *string, const struct cpumask *mask),

		 const char *string, const struct cpumask *mask,

		 const char *fmt, va_list *va),



	TP_ARGS(foo, bar, lst, string, mask),

	TP_ARGS(foo, bar, lst, string, mask, fmt, va),



	TP_STRUCT__entry(

		__array(	char,	foo,    10		)
@@ -266,6 +288,7 @@ TRACE_EVENT(foo_bar, 
		__dynamic_array(int,	list,   __length_of(lst))

		__string(	str,	string			)

		__bitmask(	cpus,	num_possible_cpus()	)

		__vstring(	vstr,	fmt,	va		)

	),



	TP_fast_assign(
@@ -274,10 +297,11 @@ TRACE_EVENT(foo_bar, 
		memcpy(__get_dynamic_array(list), lst,

		       __length_of(lst) * sizeof(int));

		__assign_str(str, string);

		__assign_vstr(vstr, fmt, va);

		__assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus());

	),



	TP_printk("foo %s %d %s %s %s %s (%s)", __entry->foo, __entry->bar,

	TP_printk("foo %s %d %s %s %s %s (%s) %s", __entry->foo, __entry->bar,



/*

 * Notice here the use of some helper functions. This includes:
@@ -321,7 +345,7 @@ TRACE_EVENT(foo_bar, 
		  __print_array(__get_dynamic_array(list),

				__get_dynamic_array_len(list) / sizeof(int),

				sizeof(int)),

		  __get_str(str), __get_bitmask(cpus))

		  __get_str(str), __get_bitmask(cpus), __get_str(vstr))

);



/*