Commit d20e3b03 authored by Steven Rostedt's avatar Steven Rostedt
Browse files

tracing: add TRACE_FIELD_SPECIAL to record complex entries



Tom Zanussi pointed out that the simple TRACE_FIELD was not enough to
record trace data that required memcpy. This patch addresses this issue
by adding a TRACE_FIELD_SPECIAL. The format is similar to TRACE_FIELD
but looks like so:

  TRACE_FIELD_SPECIAL(type_item, item, cmd)

What TRACE_FIELD gave was:

  TRACE_FIELD(type, item, assign)

The TRACE_FIELD would be used in declaring a structure:

  struct {
	type	item;
  };

And later assign it via:

  entry->item = assign;

What TRACE_FIELD_SPECIAL gives us is:

In the declaration of the structure:

  struct {
	type_item;
  };

And the assignment:

  cmd;

This change log will explain the one example used in the patch:

 TRACE_EVENT_FORMAT(sched_switch,
	TPPROTO(struct rq *rq, struct task_struct *prev,
		struct task_struct *next),
	TPARGS(rq, prev, next),
	TPFMT("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,
				    TPCMD(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)
	),
	TPRAWFMT("prev %d:%d ==> next %s:%d:%d")
	);

 The struct will be create as:

  struct {
	pid_t		prev_pid;
	int		prev_prio;
	char next_comm[TASK_COMM_LEN];
	pid_t		next_pid;
	int		next_prio;
  };

Note the TRACE_ENTRY in the cmd part of TRACE_SPECIAL. TRACE_ENTRY will
be set by the tracer to point to the structure inside the trace buffer.

  entry->prev_pid	= prev->pid;
  entry->prev_prio	= prev->prio;
  memcpy(entry->next_comm, next->comm, TASK_COMM_LEN);
  entry->next_pid	= next->pid;
  entry->next_prio	= next->prio
Reported-by: default avatarTom Zanussi <tzanussi@gmail.com>
Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
parent f2034f1e
......@@ -71,10 +71,15 @@ TRACE_EVENT_FORMAT(sched_switch,
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,
TPCMD(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)
),
TPRAWFMT("prev %d:%d ==> next %d:%d")
TPRAWFMT("prev %d:%d ==> next %s:%d:%d")
);
TRACE_EVENT_FORMAT(sched_migrate_task,
......
......@@ -30,5 +30,7 @@
#define TRACE_FIELD(type, item, assign) \
type item;
#define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
type_item;
#include <trace/trace_event_types.h>
......@@ -39,6 +39,10 @@
#define TRACE_FIELD(type, item, assign) \
field->item,
#undef TRACE_FIELD_SPECIAL
#define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
field->item,
#undef TPRAWFMT
#define TPRAWFMT(args...) args
......
......@@ -147,6 +147,20 @@ __attribute__((section("_ftrace_events"))) event_##call = { \
#define TRACE_FIELD(type, item, assign)\
entry->item = assign;
#undef TRACE_FIELD
#define TRACE_FIELD(type, item, assign)\
entry->item = assign;
#undef TPCMD
#define TPCMD(cmd...) cmd
#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) \
_TRACE_FORMAT(call, PARAMS(proto), PARAMS(args), PARAMS(fmt)) \
......
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