[RFC PATCH 4/6] tracing: add TRACE_EVENT_MAP

[Julien Desfossez]

This macro allows to create an alias of an existing TRACE_EVENT. A
TRACE_EVENT_MAP connects a new probe to an existing tracepoint, so we
can use it to create another output of the same tracepoint without
changing the instrumented code.

This allows to create alternate versions of existing tracepoints to
output more/other fields only in specific use-cases and not all the time
(which could break existing tools and/or bloat the trace with too many
useless fields).

The usage is the same as the TRACE_EVENT macro with the addition of the
"map" parameter which is the name of the alias, the "name" field is the
name of the original tracepoint:
TRACE_EVENT_MAP(name, map, proto, args, tstruct, assign, print)
DEFINE_EVENT_MAP(template, name, map, proto, args)

Cc: Peter Zijlstra 
Cc: Steven Rostedt (Red Hat) 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Mathieu Desnoyers 
Signed-off-by: Julien Desfossez 
---
 include/linux/trace_events.h | 14 -
 include/linux/tracepoint.h   | 11 +-
 include/trace/define_trace.h |  4 
 include/trace/perf.h |  7 +++
 include/trace/trace_events.h | 50 
 kernel/trace/trace_events.c  | 15 +
 6 files changed, 95 insertions(+), 6 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index be00761..1f7e0ec 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -217,6 +217,7 @@ enum {
TRACE_EVENT_FL_TRACEPOINT_BIT,
TRACE_EVENT_FL_KPROBE_BIT,
TRACE_EVENT_FL_UPROBE_BIT,
+   TRACE_EVENT_FL_MAP_BIT,
 };
 
 /*
@@ -231,6 +232,7 @@ enum {
  *  TRACEPOINT- Event is a tracepoint
  *  KPROBE- Event is a kprobe
  *  UPROBE- Event is a uprobe
+ *  MAP   - Event maps to a tracepoint as an alias
  */
 enum {
TRACE_EVENT_FL_FILTERED = (1 << TRACE_EVENT_FL_FILTERED_BIT),
@@ -241,10 +243,16 @@ enum {
TRACE_EVENT_FL_TRACEPOINT   = (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
TRACE_EVENT_FL_KPROBE   = (1 << TRACE_EVENT_FL_KPROBE_BIT),
TRACE_EVENT_FL_UPROBE   = (1 << TRACE_EVENT_FL_UPROBE_BIT),
+   TRACE_EVENT_FL_MAP  = (1 << TRACE_EVENT_FL_MAP_BIT),
 };
 
 #define TRACE_EVENT_FL_UKPROBE (TRACE_EVENT_FL_KPROBE | TRACE_EVENT_FL_UPROBE)
 
+struct trace_event_map {
+   struct tracepoint   *tp;
+   char*name;
+};
+
 struct trace_event_call {
struct list_headlist;
struct trace_event_class *class;
@@ -252,6 +260,8 @@ struct trace_event_call {
char*name;
/* Set TRACE_EVENT_FL_TRACEPOINT flag when using "tp" */
struct tracepoint   *tp;
+   /* Set TRACE_EVENT_FL_MAP flag when using "map" instead */
+   struct trace_event_map  *map;
};
struct trace_event  event;
char*print_fmt;
@@ -282,7 +292,9 @@ struct trace_event_call {
 static inline const char *
 trace_event_name(struct trace_event_call *call)
 {
-   if (call->flags & TRACE_EVENT_FL_TRACEPOINT)
+   if (call->flags & TRACE_EVENT_FL_MAP)
+   return call->map->name;
+   else if (call->flags & TRACE_EVENT_FL_TRACEPOINT)
return call->tp ? call->tp->name : NULL;
else
return call->name;
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index be586c6..b8ab12a 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -276,6 +276,7 @@ static inline void tracepoint_synchronize_unregister(void)
 
 #define DEFINE_TRACE_FN(name, reg, unreg)
 #define DEFINE_TRACE(name)
+#define DEFINE_TRACE_MAP(name, map)
 #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
 #define EXPORT_TRACEPOINT_SYMBOL(name)
 
@@ -466,6 +467,13 @@ static inline void tracepoint_synchronize_unregister(void)
  *
  * A set of (un)registration functions can be passed to the variant
  * TRACE_EVENT_FN to perform any (un)registration work.
+ *
+ * TRACE_EVENT_MAP can be used to create alternate versions of a
+ * TRACE_EVENT without modifying the instrumented code. It connects
+ * a different probe to an existing tracepoint, so other fields can be
+ * extracted. The "name" field is the name of the original TRACE_EVENT,
+ * the "map" field is the name of the alias. They can be enabled
+ * independently.
  */
 
 #define DECLARE_EVENT_CLASS(name, proto, args, tstruct, assign, print)
@@ -493,9 +501,10 @@ static inline void tracepoint_synchronize_unregister(void)
  struct, assign, print)\
DECLARE_TRACE_CONDITION(name, PARAMS(proto),\
PARAMS(args), PARAMS(cond))
-
 #define TRACE_EVENT_FLAGS(event, flag)
 
 #define 

[RFC PATCH 4/6] tracing: add TRACE_EVENT_MAP

[Julien Desfossez]

This macro allows to create an alias of an existing TRACE_EVENT. A
TRACE_EVENT_MAP connects a new probe to an existing tracepoint, so we
can use it to create another output of the same tracepoint without
changing the instrumented code.

This allows to create alternate versions of existing tracepoints to
output more/other fields only in specific use-cases and not all the time
(which could break existing tools and/or bloat the trace with too many
useless fields).

The usage is the same as the TRACE_EVENT macro with the addition of the
"map" parameter which is the name of the alias, the "name" field is the
name of the original tracepoint:
TRACE_EVENT_MAP(name, map, proto, args, tstruct, assign, print)
DEFINE_EVENT_MAP(template, name, map, proto, args)

Cc: Peter Zijlstra 
Cc: Steven Rostedt (Red Hat) 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Mathieu Desnoyers 
Signed-off-by: Julien Desfossez 
---
 include/linux/trace_events.h | 14 -
 include/linux/tracepoint.h   | 11 +-
 include/trace/define_trace.h |  4 
 include/trace/perf.h |  7 +++
 include/trace/trace_events.h | 50 
 kernel/trace/trace_events.c  | 15 +
 6 files changed, 95 insertions(+), 6 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index be00761..1f7e0ec 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -217,6 +217,7 @@ enum {
TRACE_EVENT_FL_TRACEPOINT_BIT,
TRACE_EVENT_FL_KPROBE_BIT,
TRACE_EVENT_FL_UPROBE_BIT,
+   TRACE_EVENT_FL_MAP_BIT,
 };
 
 /*
@@ -231,6 +232,7 @@ enum {
  *  TRACEPOINT- Event is a tracepoint
  *  KPROBE- Event is a kprobe
  *  UPROBE- Event is a uprobe
+ *  MAP   - Event maps to a tracepoint as an alias
  */
 enum {
TRACE_EVENT_FL_FILTERED = (1 << TRACE_EVENT_FL_FILTERED_BIT),
@@ -241,10 +243,16 @@ enum {
TRACE_EVENT_FL_TRACEPOINT   = (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
TRACE_EVENT_FL_KPROBE   = (1 << TRACE_EVENT_FL_KPROBE_BIT),
TRACE_EVENT_FL_UPROBE   = (1 << TRACE_EVENT_FL_UPROBE_BIT),
+   TRACE_EVENT_FL_MAP  = (1 << TRACE_EVENT_FL_MAP_BIT),
 };
 
 #define TRACE_EVENT_FL_UKPROBE (TRACE_EVENT_FL_KPROBE | TRACE_EVENT_FL_UPROBE)
 
+struct trace_event_map {
+   struct tracepoint   *tp;
+   char*name;
+};
+
 struct trace_event_call {
struct list_headlist;
struct trace_event_class *class;
@@ -252,6 +260,8 @@ struct trace_event_call {
char*name;
/* Set TRACE_EVENT_FL_TRACEPOINT flag when using "tp" */
struct tracepoint   *tp;
+   /* Set TRACE_EVENT_FL_MAP flag when using "map" instead */
+   struct trace_event_map  *map;
};
struct trace_event  event;
char*print_fmt;
@@ -282,7 +292,9 @@ struct trace_event_call {
 static inline const char *
 trace_event_name(struct trace_event_call *call)
 {
-   if (call->flags & TRACE_EVENT_FL_TRACEPOINT)
+   if (call->flags & TRACE_EVENT_FL_MAP)
+   return call->map->name;
+   else if (call->flags & TRACE_EVENT_FL_TRACEPOINT)
return call->tp ? call->tp->name : NULL;
else
return call->name;
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index be586c6..b8ab12a 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -276,6 +276,7 @@ static inline void tracepoint_synchronize_unregister(void)
 
 #define DEFINE_TRACE_FN(name, reg, unreg)
 #define DEFINE_TRACE(name)
+#define DEFINE_TRACE_MAP(name, map)
 #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
 #define EXPORT_TRACEPOINT_SYMBOL(name)
 
@@ -466,6 +467,13 @@ static inline void tracepoint_synchronize_unregister(void)
  *
  * A set of (un)registration functions can be passed to the variant
  * TRACE_EVENT_FN to perform any (un)registration work.
+ *
+ * TRACE_EVENT_MAP can be used to create alternate versions of a
+ * TRACE_EVENT without modifying the instrumented code. It connects
+ * a different probe to an existing tracepoint, so other fields can be
+ * extracted. The "name" field is the name of the original TRACE_EVENT,
+ * the "map" field is the name of the alias. They can be enabled
+ * independently.
  */
 
 #define DECLARE_EVENT_CLASS(name, proto, args, tstruct, assign, print)
@@ -493,9 +501,10 @@ static inline void tracepoint_synchronize_unregister(void)
  struct, assign, print)\
DECLARE_TRACE_CONDITION(name, PARAMS(proto),\
PARAMS(args), PARAMS(cond))
-
 #define TRACE_EVENT_FLAGS(event, flag)
 
 #define TRACE_EVENT_PERF_PERM(event, expr...)
 
+#define TRACE_EVENT_MAP(name, map, proto, args, struct, assign, print)
+
 #endif /* ifdef TRACE_EVENT (see note