tracing: Use dyn_event framework for synthetic events

Use dyn_event framework for synthetic events. This shows
synthetic events on "tracing/dynamic_events" file in addition
to tracing/synthetic_events interface.

User can also define new events via tracing/dynamic_events
with "s:" prefix. So, the new syntax is below;

  s:[synthetic/]EVENT_NAME TYPE ARG; [TYPE ARG;]...

To remove events via tracing/dynamic_events, you can use
"-:" prefix as same as other events.

Link: http://lkml.kernel.org/r/154140861301.17322.15454611233735614508.stgit@devboxReviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -635,6 +635,7 @@ config HIST_TRIGGERS
 	depends on ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select TRACING_MAP
 	select TRACING
+	select DYNAMIC_EVENTS
 	default n
 	help
 	  Hist triggers allow one or more arbitrary trace event fields

kernel/trace/trace.c

@@ -4620,6 +4620,9 @@ static const char readme_msg[] =
 	"\t  accepts: event-definitions (one definition per line)\n"
 	"\t   Format: p[:[<group>/]<event>] <place> [<args>]\n"
 	"\t           r[maxactive][:[<group>/]<event>] <place> [<args>]\n"
+#ifdef CONFIG_HIST_TRIGGERS
+	"\t           s:[synthetic/]<event> <field> [<field>]\n"
+#endif
 	"\t           -:[<group>/]<event>\n"
 #ifdef CONFIG_KPROBE_EVENTS
 	"\t    place: [<module>:]<symbol>[+<offset>]|<memaddr>\n"
@@ -4638,6 +4641,11 @@ static const char readme_msg[] =
 	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n"
 	"\t           b<bit-width>@<bit-offset>/<container-size>,\n"
 	"\t           <type>\\[<array-size>\\]\n"
+#ifdef CONFIG_HIST_TRIGGERS
+	"\t    field: <stype> <name>;\n"
+	"\t    stype: u8/u16/u32/u64, s8/s16/s32/s64, pid_t,\n"
+	"\t           [unsigned] char/int/long\n"
+#endif
 #endif
 	"  events/\t\t- Directory containing all trace event subsystems:\n"
 	"      enable\t\t- Write 0/1 to enable/disable tracing of all events\n"