trace: better manage the context info for events

Impact: make trace_event more convenient for tracers

All tracers (for the moment) that use the struct trace_event want to
have the context info printed before their own output: the pid/cmdline,
cpu, and timestamp.

But some other tracers that want to implement their trace_event
callbacks will not necessary need these information or they may want to
format them as they want.

This patch adds a new default-enabled trace option:
TRACE_ITER_CONTEXT_INFO When disabled through:

echo nocontext-info > /debugfs/tracing/trace_options

The pid, cpu and timestamps headers will not be printed.

IE with the sched_switch tracer with context-info (default):

     bash-2935 [001] 100.356561: 2935:120:S ==> [001]  0:140:R <idle>
   <idle>-0    [000] 100.412804:    0:140:R   + [000] 11:115:S events/0
   <idle>-0    [000] 100.412816:    0:140:R ==> [000] 11:115:R events/0
 events/0-11   [000] 100.412829:   11:115:S ==> [000]  0:140:R <idle>

Without context-info:

 2935:120:S ==> [001]  0:140:R <idle>
    0:140:R   + [000] 11:115:S events/0
    0:140:R ==> [000] 11:115:R events/0
   11:115:S ==> [000]  0:140:R <idle>

A tracer can disable it at runtime by clearing the bit
TRACE_ITER_CONTEXT_INFO in trace_flags.

The print routines were renamed to trace_print_context and
trace_print_lat_context, so that they can be used by tracers if they
want to use them for one of the trace_event callbacks.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e603a291134b..f0c7a0f08cac 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -405,6 +405,10 @@ void init_tracer_sysprof_debugfs(struct dentry *d_tracer);
 
 struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
                                                 struct trace_array_cpu *data);
+
+struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
+                                          int *ent_cpu, u64 *ent_ts);
+
 void tracing_generic_entry_update(struct trace_entry *entry,
                                   unsigned long flags,
                                   int pc);
@@ -591,7 +595,8 @@ enum trace_iterator_flags {
         TRACE_ITER_ANNOTATE             = 0x2000,
         TRACE_ITER_USERSTACKTRACE       = 0x4000,
         TRACE_ITER_SYM_USEROBJ          = 0x8000,
-        TRACE_ITER_PRINTK_MSGONLY       = 0x10000
+        TRACE_ITER_PRINTK_MSGONLY       = 0x10000,
+        TRACE_ITER_CONTEXT_INFO         = 0x20000 /* Print pid/cpu/time */
 };
 
 /*