* If TRACE_SYSTEM is defined, that will be the directory created
* 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.
* In this case, it would look for sample.h
* If the header name will be different than the system name
* (as in this case), then you can override the header name that
* define_trace.h will look up by defining TRACE_INCLUDE_FILE
* This file is called trace-events-sample.h but we want the system
* to be called "sample". Therefore we must define the name of this
* #define TRACE_INCLUDE_FILE trace-events-sample
* As we do an the bottom of this file.
* Notice that TRACE_SYSTEM should be defined outside of #if
* protection, just like TRACE_INCLUDE_FILE.
#define TRACE_SYSTEM sample
* Notice that this file is not protected like a normal header.
* We also must allow for rereading of this file. The
* || defined(TRACE_HEADER_MULTI_READ)
* serves this purpose.
#if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ)
* All trace headers should include tracepoint.h, until we finally
* make it into a standard header.
* The TRACE_EVENT macro is broken up into 5 parts.
* name: name of the trace point. This is also how to enable the tracepoint.
* A function called trace_foo_bar() will be created.
* proto: the prototype of the function trace_foo_bar()
* Here it is trace_foo_bar(char *foo, int bar).
* args: must match the arguments in the prototype.
* Here it is simply "foo, bar".
* struct: This defines the way the data will be stored in the ring buffer.
* 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;
* Assigning arrays can be done like any array:
* __entry->foo = '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);
* fast_assign: This is a C like function that is used to store the items
* 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
* 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
* 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.
static inline int __length_of(const int *list)
for (i = 0; list[i]; i++)
TP_PROTO(const char *foo, int bar, const int *lst,
const char *string, const struct cpumask *mask),
TP_ARGS(foo, bar, lst, string, mask),
__array( char, foo, 10 )
__field( int, bar )
__dynamic_array(int, list, __length_of(lst))
__string( str, string )
__bitmask( cpus, num_possible_cpus() )
strlcpy(__entry->foo, foo, 10);
__entry->bar = bar;
__length_of(lst) * sizeof(int));
__assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus());
TP_printk("foo %s %d %s %s (%s)", __entry->foo, __entry->bar,
/***** NOTICE! The #if protection ends here. *****/
* There are several ways I could have done this. If I left out the
* TRACE_INCLUDE_PATH, then it would default to the kernel source
* include/trace/events directory.
* I could specify a path from the define_trace.h file back to this
* #define TRACE_INCLUDE_PATH ../../samples/trace_events
* But the safest and easiest way to simply make it use the directory
* that the file is in is to add in the Makefile:
* CFLAGS_trace-events-sample.o := -I$(src)
* This will make sure the current path is part of the include
* structure for our file so that define_trace.h can find it.
* I could have made only the top level directory the include:
* CFLAGS_trace-events-sample.o := -I$(PWD)
* And then let the path to this directory be the TRACE_INCLUDE_PATH:
* #define TRACE_INCLUDE_PATH samples/trace_events
* But then if something defines "samples" or "trace_events" as a macro
* then we could risk that being converted too, and give us an unexpected
#define TRACE_INCLUDE_PATH .
* TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal
#define TRACE_INCLUDE_FILE trace-events-sample