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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: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2022-07-15 17:55:55 -04:00
parent f5eab65ff2
commit fea6ac554d
2 changed files with 40 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
samples/trace_events/trace-events-sample.c
View File

@ -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;

32
samples/trace_events/trace-events-sample.h
View File

@ -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))
);
/*