* If TRACE_SYSTEM is defined, that will be the directory created
* in the ftrace directory under /sys/kernel/debug/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.
* There are currently two types of elements. __field and __array.
* a __field is broken up into (type, name). Where type can be any
* type but 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.
* __array( char, foo, 10) is the same as saying char foo.
* fast_assign: This is a C like function that is used to store the items
* into the ring buffer.
* 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.
* 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_PROTO(char *foo, int bar),
__array( char, foo, 10 )
__field( int, bar )
strncpy(__entry->foo, foo, 10);
__entry->bar = bar;
TP_printk("foo %s %d", __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