/*
* If TRACE_SYSTEM is defined, that will be the directory created
- * in the ftrace directory under /sys/kernel/debug/tracing/events/<system>
+ * in the ftrace directory under /sys/kernel/tracing/events/<system>
*
* The define_trace.h below will also look for a file name of
* TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
* Here it is simply "foo, bar".
*
* struct: This defines the way the data will be stored in the ring buffer.
- * There are currently two types of elements. __field and __array.
- * a __field is broken up into (type, name). Where type can be any
- * primitive type (integer, long or pointer). __field_struct() can
- * be any static complex data value (struct, union, but not an array).
- * For an array. there are three fields. (type, name, size). The
- * type of elements in the array, the name of the field and the size
- * of the array.
+ * The items declared here become part of a special structure
+ * called "__entry", which can be used in the fast_assign part of the
+ * TRACE_EVENT macro.
+ *
+ * Here are the currently defined types you can use:
+ *
+ * __field : Is broken up into type and name. Where type can be any
+ * primitive type (integer, long or pointer).
+ *
+ * __field(int, foo)
+ *
+ * __entry->foo = 5;
+ *
+ * __field_struct : This can be any static complex data type (struct, union
+ * but not an array). Be careful using complex types, as each
+ * event is limited in size, and copying large amounts of data
+ * into the ring buffer can slow things down.
+ *
+ * __field_struct(struct bar, foo)
+ *
+ * __entry->bar.x = y;
+
+ * __array: There are three fields (type, name, size). The type is the
+ * type of elements in teh array, the name is the name of the array.
+ * size is the number of items in the array (not the total size).
+ *
+ * __array( char, foo, 10) is the same as saying: char foo[10];
+ *
+ * Assigning arrays can be done like any array:
+ *
+ * __entry->foo[0] = 'a';
+ *
+ * memcpy(__entry->foo, bar, 10);
+ *
+ * __dynamic_array: This is similar to array, but can vary is size from
+ * instance to instance of the tracepoint being called.
+ * Like __array, this too has three elements (type, name, size);
+ * type is the type of the element, name is the name of the array.
+ * The size is different than __array. It is not a static number,
+ * but the algorithm to figure out the length of the array for the
+ * specific instance of tracepoint. Again, size is the numebr of
+ * items in the array, not the total length in bytes.
+ *
+ * __dynamic_array( int, foo, bar) is similar to: int foo[bar];
+ *
+ * Note, unlike arrays, you must use the __get_dynamic_array() macro
+ * to access the array.
+ *
+ * memcpy(__get_dynamic_array(foo), bar, 10);
+ *
+ * Notice, that "__entry" is not needed here.
+ *
+ * __string: This is a special kind of __dynamic_array. It expects to
+ * have a nul terminated character array passed to it (it allows
+ * for NULL too, which would be converted into "(null)"). __string
+ * takes two paramenter (name, src), where name is the name of
+ * the string saved, and src is the string to copy into the
+ * ring buffer.
+ *
+ * __string(foo, bar) is similar to: strcpy(foo, bar)
+ *
+ * To assign a string, use the helper macro __assign_str().
+ *
+ * __assign_str(foo, bar);
+ *
+ * In most cases, the __assign_str() macro will take the same
+ * parameters as the __string() macro had to declare the string.
+ *
+ * __bitmask: This is another kind of __dynamic_array, but it expects
+ * an array of longs, and the number of bits to parse. It takes
+ * two parameters (name, nr_bits), where name is the name of the
+ * bitmask to save, and the nr_bits is the number of bits to record.
+ *
+ * __bitmask(target_cpu, nr_cpumask_bits)
+ *
+ * To assign a bitmask, use the __assign_bitmask() helper macro.
+ *
+ * __assign_bitmask(target_cpus, cpumask_bits(bar), nr_cpumask_bits);
*
- * __array( char, foo, 10) is the same as saying char foo[10].
*
* fast_assign: This is a C like function that is used to store the items
- * into the ring buffer.
+ * into the ring buffer. A special variable called "__entry" will be the
+ * structure that points into the ring buffer and has the same fields as
+ * described by the struct part of TRACE_EVENT above.
*
* printk: This is a way to print out the data in pretty print. This is
* useful if the system crashes and you are logging via a serial line,
* the data can be printed to the console using this "printk" method.
+ * This is also used to print out the data from the trace files.
+ * Again, the __entry macro is used to access the data from the ring buffer.
+ *
+ * Note, __dynamic_array, __string, and __bitmask require special helpers
+ * to access the data.
+ *
+ * For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo)
+ * Use __get_dynamic_array_len(foo) to get the length of the array
+ * saved.
+ *
+ * For __string(foo, bar) use __get_str(foo)
+ *
+ * For __bitmask(target_cpus, nr_cpumask_bits) use __get_bitmask(target_cpus)
+ *
*
* Note, that for both the assign and the printk, __entry is the handler
* to the data structure in the ring buffer, and is defined by the
* TP_STRUCT__entry.
*/
+
+/*
+ * It is OK to have helper functions in the file, but they need to be protected
+ * from being defined more than once. Remember, this file gets included more
+ * than once.
+ */
+#ifndef __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS
+#define __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS
+static inline int __length_of(const int *list)
+{
+ int i;
+
+ if (!list)
+ return 0;
+
+ for (i = 0; list[i]; i++)
+ ;
+ return i;
+}
+#endif
+
TRACE_EVENT(foo_bar,
- TP_PROTO(char *foo, int bar),
+ TP_PROTO(const char *foo, int bar, const int *lst,
+ const char *string, const struct cpumask *mask),
- TP_ARGS(foo, bar),
+ TP_ARGS(foo, bar, lst, string, mask),
TP_STRUCT__entry(
__array( char, foo, 10 )
__field( int, bar )
+ __dynamic_array(int, list, __length_of(lst))
+ __string( str, string )
+ __bitmask( cpus, num_possible_cpus() )
),
TP_fast_assign(
strlcpy(__entry->foo, foo, 10);
__entry->bar = bar;
+ memcpy(__get_dynamic_array(list), lst,
+ __length_of(lst) * sizeof(int));
+ __assign_str(str, string);
+ __assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus());
+ ),
+
+ TP_printk("foo %s %d %s %s (%s)", __entry->foo, __entry->bar,
+ __print_array(__get_dynamic_array(list),
+ __get_dynamic_array_len(list),
+ sizeof(int)),
+ __get_str(str), __get_bitmask(cpus))
+);
+
+/*
+ * There may be a case where a tracepoint should only be called if
+ * some condition is set. Otherwise the tracepoint should not be called.
+ * But to do something like:
+ *
+ * if (cond)
+ * trace_foo();
+ *
+ * Would cause a little overhead when tracing is not enabled, and that
+ * overhead, even if small, is not something we want. As tracepoints
+ * use static branch (aka jump_labels), where no branch is taken to
+ * skip the tracepoint when not enabled, and a jmp is placed to jump
+ * to the tracepoint code when it is enabled, having a if statement
+ * nullifies that optimization. It would be nice to place that
+ * condition within the static branch. This is where TRACE_EVENT_CONDITION
+ * comes in.
+ *
+ * TRACE_EVENT_CONDITION() is just like TRACE_EVENT, except it adds another
+ * parameter just after args. Where TRACE_EVENT has:
+ *
+ * TRACE_EVENT(name, proto, args, struct, assign, printk)
+ *
+ * the CONDITION version has:
+ *
+ * TRACE_EVENT_CONDITION(name, proto, args, cond, struct, assign, printk)
+ *
+ * Everything is the same as TRACE_EVENT except for the new cond. Think
+ * of the cond variable as:
+ *
+ * if (cond)
+ * trace_foo_bar_with_cond();
+ *
+ * Except that the logic for the if branch is placed after the static branch.
+ * That is, the if statement that processes the condition will not be
+ * executed unless that traecpoint is enabled. Otherwise it still remains
+ * a nop.
+ */
+TRACE_EVENT_CONDITION(foo_bar_with_cond,
+
+ TP_PROTO(const char *foo, int bar),
+
+ TP_ARGS(foo, bar),
+
+ TP_CONDITION(!(bar % 10)),
+
+ TP_STRUCT__entry(
+ __string( foo, foo )
+ __field( int, bar )
+ ),
+
+ TP_fast_assign(
+ __assign_str(foo, foo);
+ __entry->bar = bar;
+ ),
+
+ TP_printk("foo %s %d", __get_str(foo), __entry->bar)
+);
+
+void foo_bar_reg(void);
+void foo_bar_unreg(void);
+
+/*
+ * Now in the case that some function needs to be called when the
+ * tracepoint is enabled and/or when it is disabled, the
+ * TRACE_EVENT_FN() serves this purpose. This is just like TRACE_EVENT()
+ * but adds two more parameters at the end:
+ *
+ * TRACE_EVENT_FN( name, proto, args, struct, assign, printk, reg, unreg)
+ *
+ * reg and unreg are functions with the prototype of:
+ *
+ * void reg(void)
+ *
+ * The reg function gets called before the tracepoint is enabled, and
+ * the unreg function gets called after the tracepoint is disabled.
+ *
+ * Note, reg and unreg are allowed to be NULL. If you only need to
+ * call a function before enabling, or after disabling, just set one
+ * function and pass in NULL for the other parameter.
+ */
+TRACE_EVENT_FN(foo_bar_with_fn,
+
+ TP_PROTO(const char *foo, int bar),
+
+ TP_ARGS(foo, bar),
+
+ TP_STRUCT__entry(
+ __string( foo, foo )
+ __field( int, bar )
+ ),
+
+ TP_fast_assign(
+ __assign_str(foo, foo);
+ __entry->bar = bar;
+ ),
+
+ TP_printk("foo %s %d", __get_str(foo), __entry->bar),
+
+ foo_bar_reg, foo_bar_unreg
+);
+
+/*
+ * Each TRACE_EVENT macro creates several helper functions to produce
+ * the code to add the tracepoint, create the files in the trace
+ * directory, hook it to perf, assign the values and to print out
+ * the raw data from the ring buffer. To prevent too much bloat,
+ * if there are more than one tracepoint that uses the same format
+ * for the proto, args, struct, assign and printk, and only the name
+ * is different, it is highly recommended to use the DECLARE_EVENT_CLASS
+ *
+ * DECLARE_EVENT_CLASS() macro creates most of the functions for the
+ * tracepoint. Then DEFINE_EVENT() is use to hook a tracepoint to those
+ * functions. This DEFINE_EVENT() is an instance of the class and can
+ * be enabled and disabled separately from other events (either TRACE_EVENT
+ * or other DEFINE_EVENT()s).
+ *
+ * Note, TRACE_EVENT() itself is simply defined as:
+ *
+ * #define TRACE_EVENT(name, proto, args, tstruct, assign, printk) \
+ * DEFINE_EVENT_CLASS(name, proto, args, tstruct, assign, printk); \
+ * DEFINE_EVENT(name, name, proto, args)
+ *
+ * The DEFINE_EVENT() also can be declared with conditions and reg functions:
+ *
+ * DEFINE_EVENT_CONDITION(template, name, proto, args, cond);
+ * DEFINE_EVENT_FN(template, name, proto, args, reg, unreg);
+ */
+DECLARE_EVENT_CLASS(foo_template,
+
+ TP_PROTO(const char *foo, int bar),
+
+ TP_ARGS(foo, bar),
+
+ TP_STRUCT__entry(
+ __string( foo, foo )
+ __field( int, bar )
+ ),
+
+ TP_fast_assign(
+ __assign_str(foo, foo);
+ __entry->bar = bar;
),
- TP_printk("foo %s %d", __entry->foo, __entry->bar)
+ TP_printk("foo %s %d", __get_str(foo), __entry->bar)
);
+
+/*
+ * Here's a better way for the previous samples (except, the first
+ * exmaple had more fields and could not be used here).
+ */
+DEFINE_EVENT(foo_template, foo_with_template_simple,
+ TP_PROTO(const char *foo, int bar),
+ TP_ARGS(foo, bar));
+
+DEFINE_EVENT_CONDITION(foo_template, foo_with_template_cond,
+ TP_PROTO(const char *foo, int bar),
+ TP_ARGS(foo, bar),
+ TP_CONDITION(!(bar % 8)));
+
+
+DEFINE_EVENT_FN(foo_template, foo_with_template_fn,
+ TP_PROTO(const char *foo, int bar),
+ TP_ARGS(foo, bar),
+ foo_bar_reg, foo_bar_unreg);
+
+/*
+ * Anytime two events share basically the same values and have
+ * the same output, use the DECLARE_EVENT_CLASS() and DEFINE_EVENT()
+ * when ever possible.
+ */
+
+/*
+ * If the event is similar to the DECLARE_EVENT_CLASS, but you need
+ * to have a different output, then use DEFINE_EVENT_PRINT() which
+ * lets you override the TP_printk() of the class.
+ */
+
+DEFINE_EVENT_PRINT(foo_template, foo_with_template_print,
+ TP_PROTO(const char *foo, int bar),
+ TP_ARGS(foo, bar),
+ TP_printk("bar %s %d", __get_str(foo), __entry->bar));
+
#endif
/***** NOTICE! The #if protection ends here. *****/
projects / karo-tx-linux.git / blobdiff