138 lines
4.2 KiB
C
138 lines
4.2 KiB
C
/*
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* If TRACE_SYSTEM is defined, that will be the directory created
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* in the ftrace directory under /sys/kernel/debug/tracing/events/<system>
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*
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* The define_trace.h below will also look for a file name of
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* TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
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* In this case, it would look for sample.h
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*
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* If the header name will be different than the system name
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* (as in this case), then you can override the header name that
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* define_trace.h will look up by defining TRACE_INCLUDE_FILE
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*
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* This file is called trace-events-sample.h but we want the system
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* to be called "sample". Therefore we must define the name of this
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* file:
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*
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* #define TRACE_INCLUDE_FILE trace-events-sample
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*
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* As we do an the bottom of this file.
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*
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* Notice that TRACE_SYSTEM should be defined outside of #if
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* protection, just like TRACE_INCLUDE_FILE.
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*/
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#undef TRACE_SYSTEM
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#define TRACE_SYSTEM sample
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/*
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* Notice that this file is not protected like a normal header.
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* We also must allow for rereading of this file. The
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*
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* || defined(TRACE_HEADER_MULTI_READ)
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*
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* serves this purpose.
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*/
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#if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _TRACE_EVENT_SAMPLE_H
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/*
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* All trace headers should include tracepoint.h, until we finally
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* make it into a standard header.
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*/
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#include <linux/tracepoint.h>
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/*
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* The TRACE_EVENT macro is broken up into 5 parts.
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*
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* name: name of the trace point. This is also how to enable the tracepoint.
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* A function called trace_foo_bar() will be created.
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*
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* proto: the prototype of the function trace_foo_bar()
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* Here it is trace_foo_bar(char *foo, int bar).
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*
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* args: must match the arguments in the prototype.
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* Here it is simply "foo, bar".
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*
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* struct: This defines the way the data will be stored in the ring buffer.
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* There are currently two types of elements. __field and __array.
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* a __field is broken up into (type, name). Where type can be any
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* type but an array.
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* For an array. there are three fields. (type, name, size). The
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* type of elements in the array, the name of the field and the size
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* of the array.
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*
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* __array( char, foo, 10) is the same as saying char foo[10].
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*
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* fast_assign: This is a C like function that is used to store the items
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* into the ring buffer.
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*
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* printk: This is a way to print out the data in pretty print. This is
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* useful if the system crashes and you are logging via a serial line,
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* the data can be printed to the console using this "printk" method.
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*
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* Note, that for both the assign and the printk, __entry is the handler
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* to the data structure in the ring buffer, and is defined by the
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* TP_STRUCT__entry.
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*/
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TRACE_EVENT(foo_bar,
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TP_PROTO(char *foo, int bar),
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TP_ARGS(foo, bar),
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TP_STRUCT__entry(
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__array( char, foo, 10 )
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__field( int, bar )
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),
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TP_fast_assign(
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strncpy(__entry->foo, foo, 10);
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__entry->bar = bar;
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),
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TP_printk("foo %s %d", __entry->foo, __entry->bar)
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);
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#endif
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/***** NOTICE! The #if protection ends here. *****/
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/*
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* There are several ways I could have done this. If I left out the
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* TRACE_INCLUDE_PATH, then it would default to the kernel source
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* include/trace/events directory.
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*
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* I could specify a path from the define_trace.h file back to this
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* file.
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*
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* #define TRACE_INCLUDE_PATH ../../samples/trace_events
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*
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* But the safest and easiest way to simply make it use the directory
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* that the file is in is to add in the Makefile:
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*
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* CFLAGS_trace-events-sample.o := -I$(src)
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*
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* This will make sure the current path is part of the include
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* structure for our file so that define_trace.h can find it.
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*
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* I could have made only the top level directory the include:
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*
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* CFLAGS_trace-events-sample.o := -I$(PWD)
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*
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* And then let the path to this directory be the TRACE_INCLUDE_PATH:
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*
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* #define TRACE_INCLUDE_PATH samples/trace_events
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*
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* But then if something defines "samples" or "trace_events" as a macro
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* then we could risk that being converted too, and give us an unexpected
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* result.
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*/
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#undef TRACE_INCLUDE_PATH
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#undef TRACE_INCLUDE_FILE
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#define TRACE_INCLUDE_PATH .
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/*
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* TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal
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*/
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#define TRACE_INCLUDE_FILE trace-events-sample
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#include <trace/define_trace.h>
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