tracing: Move synthetic events to a separate file

With the addition of the in-kernel synthetic event API, synthetic
events are no longer specifically tied to the histogram triggers.

The synthetic event code is also making trace_event_hist.c very
bloated, so for those reasons, move it to a separate file,
trace_events_synth.c, along with a new trace_synth.h header file.

Because synthetic events are now independent from hist triggers, add a
new CONFIG_SYNTH_EVENTS config option, and have CONFIG_HIST_TRIGGERS
select it, and have CONFIG_SYNTH_EVENT_GEN_TEST depend on it.

Link: http://lkml.kernel.org/r/4d1fa1f85ed5982706ac44844ac92451dcb04715.1590693308.git.zanussi@kernel.org

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -623,12 +623,30 @@ config TRACING_MAP
 	  generally used outside of that context, and is normally
 	  selected by tracers that use it.
 
+config SYNTH_EVENTS
+	bool "Synthetic trace events"
+	select TRACING
+	select DYNAMIC_EVENTS
+	default n
+	help
+	  Synthetic events are user-defined trace events that can be
+	  used to combine data from other trace events or in fact any
+	  data source.  Synthetic events can be generated indirectly
+	  via the trace() action of histogram triggers or directly
+	  by way of an in-kernel API.
+
+	  See Documentation/trace/events.rst or
+	  Documentation/trace/histogram.rst for details and examples.
+
+	  If in doubt, say N.
+
 config HIST_TRIGGERS
 	bool "Histogram triggers"
 	depends on ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select TRACING_MAP
 	select TRACING
 	select DYNAMIC_EVENTS
+	select SYNTH_EVENTS
 	default n
 	help
 	  Hist triggers allow one or more arbitrary trace event fields
@@ -824,7 +842,7 @@ config PREEMPTIRQ_DELAY_TEST
 
 config SYNTH_EVENT_GEN_TEST
 	tristate "Test module for in-kernel synthetic event generation"
-	depends on HIST_TRIGGERS
+	depends on SYNTH_EVENTS
 	help
           This option creates a test module to check the base
           functionality of in-kernel synthetic event definition and

kernel/trace/Makefile

@@ -72,6 +72,7 @@ endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
 obj-$(CONFIG_TRACE_EVENT_INJECT) += trace_events_inject.o
+obj-$(CONFIG_SYNTH_EVENTS) += trace_events_synth.o
 obj-$(CONFIG_HIST_TRIGGERS) += trace_events_hist.o
 obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o
 obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe.o

kernel/trace/trace_synth.h

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef __TRACE_SYNTH_H
+#define __TRACE_SYNTH_H
+
+#include "trace_dynevent.h"
+
+#define SYNTH_SYSTEM		"synthetic"
+#define SYNTH_FIELDS_MAX	32
+
+#define STR_VAR_LEN_MAX		32 /* must be multiple of sizeof(u64) */
+
+struct synth_field {
+	char *type;
+	char *name;
+	size_t size;
+	unsigned int offset;
+	bool is_signed;
+	bool is_string;
+};
+
+struct synth_event {
+	struct dyn_event			devent;
+	int					ref;
+	char					*name;
+	struct synth_field			**fields;
+	unsigned int				n_fields;
+	unsigned int				n_u64;
+	struct trace_event_class		class;
+	struct trace_event_call			call;
+	struct tracepoint			*tp;
+	struct module				*mod;
+};
+
+extern struct synth_event *find_synth_event(const char *name);
+
+#endif /* __TRACE_SYNTH_H */