tracing: add TRACE_FIELD_SPECIAL to record complex entries
authorSteven Rostedt <srostedt@redhat.com>
Mon, 2 Mar 2009 15:53:15 +0000 (10:53 -0500)
committerSteven Rostedt <srostedt@redhat.com>
Mon, 2 Mar 2009 15:53:15 +0000 (10:53 -0500)
commitd20e3b03842bfeb9d21817ff19054c277cc3eac0
tree5de7ef8a95f9391a264df358336842c9301f3868
parentf2034f1e1adaac6713a6d48b5a2d4f3aa3e63ccb
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: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
include/trace/sched_event_types.h
kernel/trace/trace_events_stage_1.h
kernel/trace/trace_events_stage_2.h
kernel/trace/trace_events_stage_3.h