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/*
* trace_export . c - export basic ftrace utilities to user space
*
* Copyright ( C ) 2009 Steven Rostedt < srostedt @ redhat . com >
*/
# include <linux/stringify.h>
# include <linux/kallsyms.h>
# include <linux/seq_file.h>
# include <linux/debugfs.h>
# include <linux/uaccess.h>
# include <linux/ftrace.h>
# include <linux/module.h>
# include <linux/init.h>
# include <linux/fs.h>
# include "trace_output.h"
tracing: new format for specialized trace points
Impact: clean up and enhancement
The TRACE_EVENT_FORMAT macro looks quite ugly and is limited in its
ability to save data as well as to print the record out. Working with
Ingo Molnar, we came up with a new format that is much more pleasing to
the eye of C developers. This new macro is more C style than the old
macro, and is more obvious to what it does.
Here's the example. The only updated macro in this patch is the
sched_switch trace point.
The old method looked like this:
TRACE_EVENT_FORMAT(sched_switch,
TP_PROTO(struct rq *rq, struct task_struct *prev,
struct task_struct *next),
TP_ARGS(rq, prev, next),
TP_FMT("task %s:%d ==> %s:%d",
prev->comm, prev->pid, next->comm, next->pid),
TRACE_STRUCT(
TRACE_FIELD(pid_t, prev_pid, prev->pid)
TRACE_FIELD(int, prev_prio, prev->prio)
TRACE_FIELD_SPECIAL(char next_comm[TASK_COMM_LEN],
next_comm,
TP_CMD(memcpy(TRACE_ENTRY->next_comm,
next->comm,
TASK_COMM_LEN)))
TRACE_FIELD(pid_t, next_pid, next->pid)
TRACE_FIELD(int, next_prio, next->prio)
),
TP_RAW_FMT("prev %d:%d ==> next %s:%d:%d")
);
The above method is hard to read and requires two format fields.
The new method:
/*
* Tracepoint for task switches, performed by the scheduler:
*
* (NOTE: the 'rq' argument is not used by generic trace events,
* but used by the latency tracer plugin. )
*/
TRACE_EVENT(sched_switch,
TP_PROTO(struct rq *rq, struct task_struct *prev,
struct task_struct *next),
TP_ARGS(rq, prev, next),
TP_STRUCT__entry(
__array( char, prev_comm, TASK_COMM_LEN )
__field( pid_t, prev_pid )
__field( int, prev_prio )
__array( char, next_comm, TASK_COMM_LEN )
__field( pid_t, next_pid )
__field( int, next_prio )
),
TP_printk("task %s:%d [%d] ==> %s:%d [%d]",
__entry->prev_comm, __entry->prev_pid, __entry->prev_prio,
__entry->next_comm, __entry->next_pid, __entry->next_prio),
TP_fast_assign(
memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
__entry->prev_pid = prev->pid;
__entry->prev_prio = prev->prio;
memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
__entry->next_pid = next->pid;
__entry->next_prio = next->prio;
)
);
This macro is called TRACE_EVENT, it is broken up into 5 parts:
TP_PROTO: the proto type of the trace point
TP_ARGS: the arguments of the trace point
TP_STRUCT_entry: the structure layout of the entry in the ring buffer
TP_printk: the printk format
TP_fast_assign: the method used to write the entry into the ring buffer
The structure is the definition of how the event will be saved in the
ring buffer. The printk is used by the internal tracing in case of
an oops, and the kernel needs to print out the format of the record
to the console. This the TP_printk gives a means to show the records
in a human readable format. It is also used to print out the data
from the trace file.
The TP_fast_assign is executed directly. It is basically like a C function,
where the __entry is the handle to the record.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
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# undef TRACE_STRUCT
# define TRACE_STRUCT(args...) args
# undef TRACE_FIELD
# define TRACE_FIELD(type, item, assign) \
ret = trace_seq_printf ( s , " \t field: " # type " " # item " ; \t " \
" offset:%u; \t size:%u; \n " , \
( unsigned int ) offsetof ( typeof ( field ) , item ) , \
( unsigned int ) sizeof ( field . item ) ) ; \
if ( ! ret ) \
return 0 ;
# undef TRACE_FIELD_SPECIAL
# define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
ret = trace_seq_printf ( s , " \t field special: " # type_item " ; \t " \
" offset:%u; \t size:%u; \n " , \
( unsigned int ) offsetof ( typeof ( field ) , item ) , \
( unsigned int ) sizeof ( field . item ) ) ; \
if ( ! ret ) \
return 0 ;
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# undef TRACE_FIELD_ZERO_CHAR
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# define TRACE_FIELD_ZERO_CHAR(item) \
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ret = trace_seq_printf ( s , " \t field:char " # item " ; \t " \
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" offset:%u; \t size:0; \n " , \
( unsigned int ) offsetof ( typeof ( field ) , item ) ) ; \
if ( ! ret ) \
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return 0 ;
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# undef TP_RAW_FMT
# define TP_RAW_FMT(args...) args
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# undef TRACE_EVENT_FORMAT
# define TRACE_EVENT_FORMAT(call, proto, args, fmt, tstruct, tpfmt) \
static int \
ftrace_format_ # # call ( struct trace_seq * s ) \
{ \
struct args field ; \
int ret ; \
\
tstruct ; \
\
trace_seq_printf ( s , " \n print fmt: \" %s \" \n " , tpfmt ) ; \
\
return ret ; \
}
# include "trace_event_types.h"
# undef TRACE_ZERO_CHAR
# define TRACE_ZERO_CHAR(arg)
# undef TRACE_FIELD
# define TRACE_FIELD(type, item, assign)\
entry - > item = assign ;
# undef TRACE_FIELD
# define TRACE_FIELD(type, item, assign)\
entry - > item = assign ;
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# undef TP_CMD
# define TP_CMD(cmd...) cmd
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# undef TRACE_ENTRY
# define TRACE_ENTRY entry
# undef TRACE_FIELD_SPECIAL
# define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
cmd ;
# undef TRACE_EVENT_FORMAT
# define TRACE_EVENT_FORMAT(call, proto, args, fmt, tstruct, tpfmt) \
\
static struct ftrace_event_call __used \
__attribute__ ( ( __aligned__ ( 4 ) ) ) \
__attribute__ ( ( section ( " _ftrace_events " ) ) ) event_ # # call = { \
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. name = # call , \
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. id = proto , \
. system = __stringify ( TRACE_SYSTEM ) , \
. show_format = ftrace_format_ # # call , \
}
# include "trace_event_types.h"
