tracing: Let tracepoints have data passed to tracepoint callbacks

This patch adds data to be passed to tracepoint callbacks.

The created functions from DECLARE_TRACE() now need a mandatory data
parameter. For example:

DECLARE_TRACE(mytracepoint, int value, value)

Will create the register function:

int register_trace_mytracepoint((void(*)(void *data, int value))probe,
                                void *data);

As the first argument, all callbacks (probes) must take a (void *data)
parameter. So a callback for the above tracepoint will look like:

void myprobe(void *data, int value)
{
}

The callback may choose to ignore the data parameter.

This change allows callbacks to register a private data pointer along
with the function probe.

	void mycallback(void *data, int value);

	register_trace_mytracepoint(mycallback, mydata);

Then the mycallback() will receive the "mydata" as the first parameter
before the args.

A more detailed example:

  DECLARE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status));

  /* In the C file */

  DEFINE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status));

  [...]

       trace_mytracepoint(status);

  /* In a file registering this tracepoint */

  int my_callback(void *data, int status)
  {
	struct my_struct my_data = data;
	[...]
  }

  [...]
	my_data = kmalloc(sizeof(*my_data), GFP_KERNEL);
	init_my_data(my_data);
	register_trace_mytracepoint(my_callback, my_data);

The same callback can also be registered to the same tracepoint as long
as the data registered is different. Note, the data must also be used
to unregister the callback:

	unregister_trace_mytracepoint(my_callback, my_data);

Because of the data parameter, tracepoints declared this way can not have
no args. That is:

  DECLARE_TRACE(mytracepoint, TP_PROTO(void), TP_ARGS());

will cause an error.

If no arguments are needed, a new macro can be used instead:

  DECLARE_TRACE_NOARGS(mytracepoint);

Since there are no arguments, the proto and args fields are left out.

This is part of a series to make the tracepoint footprint smaller:

   text	   data	    bss	    dec	    hex	filename
4913961	1088356	 861512	6863829	 68bbd5	vmlinux.orig
4914025	1088868	 861512	6864405	 68be15	vmlinux.class
4918492	1084612	 861512	6864616	 68bee8	vmlinux.tracepoint

Again, this patch also increases the size of the kernel, but
lays the ground work for decreasing it.

 v5: Fixed net/core/drop_monitor.c to handle these updates.

 v4: Moved the DECLARE_TRACE() DECLARE_TRACE_NOARGS out of the
     #ifdef CONFIG_TRACE_POINTS, since the two are the same in both
     cases. The __DECLARE_TRACE() is what changes.
     Thanks to Frederic Weisbecker for pointing this out.

 v3: Made all register_* functions require data to be passed and
     all callbacks to take a void * parameter as its first argument.
     This makes the calling functions comply with C standards.

     Also added more comments to the modifications of DECLARE_TRACE().

 v2: Made the DECLARE_TRACE() have the ability to pass arguments
     and added a new DECLARE_TRACE_NOARGS() for tracepoints that
     do not need any arguments.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 72 insertions, 23 deletions

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 8d5e4f6d96d0..9a59d1f98cd4 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -20,12 +20,17 @@
 struct module;
 struct tracepoint;
 
+struct tracepoint_func {
+        void *func;
+        void *data;
+};
+
 struct tracepoint {
         const char *name;               /* Tracepoint name */
         int state;                      /* State. */
         void (*regfunc)(void);
         void (*unregfunc)(void);
-        void **funcs;
+        struct tracepoint_func *funcs;
 } __attribute__((aligned(32)));         /*
                                          * Aligned on 32 bytes because it is
                                          * globally visible and gcc happily
@@ -37,16 +42,19 @@ struct tracepoint {
  * Connect a probe to a tracepoint.
  * Internal API, should not be used directly.
  */
-extern int tracepoint_probe_register(const char *name, void *probe);
+extern int tracepoint_probe_register(const char *name, void *probe, void *data);
 
 /*
  * Disconnect a probe from a tracepoint.
  * Internal API, should not be used directly.
  */
-extern int tracepoint_probe_unregister(const char *name, void *probe);
+extern int
+tracepoint_probe_unregister(const char *name, void *probe, void *data);
 
-extern int tracepoint_probe_register_noupdate(const char *name, void *probe);
-extern int tracepoint_probe_unregister_noupdate(const char *name, void *probe);
+extern int tracepoint_probe_register_noupdate(const char *name, void *probe,
+                                              void *data);
+extern int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
+                                                void *data);
 extern void tracepoint_probe_update_all(void);
 
 struct tracepoint_iter {
@@ -102,17 +110,27 @@ static inline void tracepoint_update_probe_range(struct tracepoint *begin,
 /*
  * it_func[0] is never NULL because there is at least one element in the array
  * when the array itself is non NULL.
+ *
+ * Note, the proto and args passed in includes "__data" as the first parameter.
+ * The reason for this is to handle the "void" prototype. If a tracepoint
+ * has a "void" prototype, then it is invalid to declare a function
+ * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just
+ * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto".
  */
 #define __DO_TRACE(tp, proto, args)                                     \
         do {                                                            \
-                void **it_func;                                         \
+                struct tracepoint_func *it_func_ptr;                    \
+                void *it_func;                                          \
+                void *__data;                                           \
                                                                         \
                 rcu_read_lock_sched_notrace();                          \
-                it_func = rcu_dereference_sched((tp)->funcs);           \
-                if (it_func) {                                          \
+                it_func_ptr = rcu_dereference_sched((tp)->funcs);       \
+                if (it_func_ptr) {                                      \
                         do {                                            \
-                                ((void(*)(proto))(*it_func))(args);     \
-                        } while (*(++it_func));                         \
+                                it_func = (it_func_ptr)->func;          \
+                                __data = (it_func_ptr)->data;           \
+                                ((void(*)(proto))(it_func))(args);      \
+                        } while ((++it_func_ptr)->func);                \
                 }                                                       \
                 rcu_read_unlock_sched_notrace();                        \
         } while (0)
@@ -122,23 +140,29 @@ static inline void tracepoint_update_probe_range(struct tracepoint *begin,
  * not add unwanted padding between the beginning of the section and the
  * structure. Force alignment to the same alignment as the section start.
  */
-#define DECLARE_TRACE(name, proto, args)                                \
+#define __DECLARE_TRACE(name, proto, args, data_proto, data_args)       \
         extern struct tracepoint __tracepoint_##name;                   \
         static inline void trace_##name(proto)                          \
         {                                                               \
                 if (unlikely(__tracepoint_##name.state))                \
                         __DO_TRACE(&__tracepoint_##name,                \
-                                TP_PROTO(proto), TP_ARGS(args));        \
+                                TP_PROTO(data_proto),                   \
+                                TP_ARGS(data_args));                    \
         }                                                               \
-        static inline int register_trace_##name(void (*probe)(proto))   \
+        static inline int                                               \
+        register_trace_##name(void (*probe)(data_proto), void *data)    \
         {                                                               \
-                return tracepoint_probe_register(#name, (void *)probe); \
+                return tracepoint_probe_register(#name, (void *)probe,  \
+                                                 data);                 \
         }                                                               \
-        static inline int unregister_trace_##name(void (*probe)(proto)) \
+        static inline int                                               \
+        unregister_trace_##name(void (*probe)(data_proto), void *data)  \
         {                                                               \
-                return tracepoint_probe_unregister(#name, (void *)probe);\
+                return tracepoint_probe_unregister(#name, (void *)probe, \
+                                                   data);               \
         }                                                               \
-        static inline void check_trace_callback_type_##name(void (*cb)(proto)) \
+        static inline void                                              \
+        check_trace_callback_type_##name(void (*cb)(data_proto))        \
         {                                                               \
         }
 
@@ -158,20 +182,22 @@ static inline void tracepoint_update_probe_range(struct tracepoint *begin,
         EXPORT_SYMBOL(__tracepoint_##name)
 
 #else /* !CONFIG_TRACEPOINTS */
-#define DECLARE_TRACE(name, proto, args)                                \
-        static inline void _do_trace_##name(struct tracepoint *tp, proto) \
-        { }                                                             \
+#define __DECLARE_TRACE(name, proto, args, data_proto, data_args)       \
         static inline void trace_##name(proto)                          \
         { }                                                             \
-        static inline int register_trace_##name(void (*probe)(proto))   \
+        static inline int                                               \
+        register_trace_##name(void (*probe)(data_proto),                \
+                              void *data)                               \
         {                                                               \
                 return -ENOSYS;                                         \
         }                                                               \
-        static inline int unregister_trace_##name(void (*probe)(proto)) \
+        static inline int                                               \
+        unregister_trace_##name(void (*probe)(data_proto),              \
+                                void *data)                             \
         {                                                               \
                 return -ENOSYS;                                         \
         }                                                               \
-        static inline void check_trace_callback_type_##name(void (*cb)(proto)) \
+        static inline void check_trace_callback_type_##name(void (*cb)(data_proto)) \
         {                                                               \
         }
 
@@ -181,6 +207,29 @@ static inline void tracepoint_update_probe_range(struct tracepoint *begin,
 #define EXPORT_TRACEPOINT_SYMBOL(name)
 
 #endif /* CONFIG_TRACEPOINTS */
+
+/*
+ * The need for the DECLARE_TRACE_NOARGS() is to handle the prototype
+ * (void). "void" is a special value in a function prototype and can
+ * not be combined with other arguments. Since the DECLARE_TRACE()
+ * macro adds a data element at the beginning of the prototype,
+ * we need a way to differentiate "(void *data, proto)" from
+ * "(void *data, void)". The second prototype is invalid.
+ *
+ * DECLARE_TRACE_NOARGS() passes "void" as the tracepoint prototype
+ * and "void *__data" as the callback prototype.
+ *
+ * DECLARE_TRACE() passes "proto" as the tracepoint protoype and
+ * "void *__data, proto" as the callback prototype.
+ */
+#define DECLARE_TRACE_NOARGS(name)                                      \
+                __DECLARE_TRACE(name, void, , void *__data, __data)
+
+#define DECLARE_TRACE(name, proto, args)                                \
+                __DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),      \
+                                PARAMS(void *__data, proto),            \
+                                PARAMS(__data, args))
+
 #endif /* DECLARE_TRACE */
 
 #ifndef TRACE_EVENT