trace: Add trace-events file for declaring trace events

This patch introduces the trace-events file where trace events can be
declared like so:

qemu_malloc(size_t size) "size %zu"
qemu_free(void *ptr) "ptr %p"

These trace event declarations are processed by a new tool called
tracetool to generate code for the trace events.  Trace event
declarations are independent of the backend tracing system (LTTng User
Space Tracing, ftrace markers, DTrace).

The default "nop" backend generates empty trace event functions.
Therefore trace events are disabled by default.

The trace-events file serves two purposes:

1. Adding trace events is easy.  It is not necessary to understand the
   details of a backend tracing system.  The trace-events file is a
   single location where trace events can be declared without code
   duplication.

2. QEMU is not tightly coupled to one particular backend tracing system.
   In order to support tracing across QEMU host platforms and to
   anticipate new backend tracing systems that are currently maturing,
   it is important to be flexible and not tied to one system.

This commit includes fixes from Prerna Saxena
<prerna@linux.vnet.ibm.com> and Blue Swirl <blauwirbel@gmail.com>.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index f95cc2fd01..3c5e6a060e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 # Makefile for QEMU.
 
-GENERATED_HEADERS = config-host.h
+GENERATED_HEADERS = config-host.h trace.h
 
 ifneq ($(wildcard config-host.mak),)
 # Put the all: rule here so that config-host.mak can contain dependencies.
@@ -104,16 +104,24 @@ ui/vnc.o: QEMU_CFLAGS += $(VNC_TLS_CFLAGS)
 
 bt-host.o: QEMU_CFLAGS += $(BLUEZ_CFLAGS)
 
+trace.h: $(SRC_PATH)/trace-events config-host.mak
+	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -h < $< > $@,"  GEN   $@")
+
+trace.c: $(SRC_PATH)/trace-events config-host.mak
+	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -c < $< > $@,"  GEN   $@")
+
+trace.o: trace.c $(GENERATED_HEADERS)
+
 ######################################################################
 
 qemu-img.o: qemu-img-cmds.h
 qemu-img.o qemu-tool.o qemu-nbd.o qemu-io.o: $(GENERATED_HEADERS)
 
-qemu-img$(EXESUF): qemu-img.o qemu-tool.o qemu-error.o $(block-obj-y) $(qobject-obj-y)
+qemu-img$(EXESUF): qemu-img.o qemu-tool.o qemu-error.o $(trace-obj-y) $(block-obj-y) $(qobject-obj-y)
 
-qemu-nbd$(EXESUF): qemu-nbd.o qemu-tool.o qemu-error.o $(block-obj-y) $(qobject-obj-y)
+qemu-nbd$(EXESUF): qemu-nbd.o qemu-tool.o qemu-error.o $(trace-obj-y) $(block-obj-y) $(qobject-obj-y)
 
-qemu-io$(EXESUF): qemu-io.o cmd.o qemu-tool.o qemu-error.o $(block-obj-y) $(qobject-obj-y)
+qemu-io$(EXESUF): qemu-io.o cmd.o qemu-tool.o qemu-error.o $(trace-obj-y) $(block-obj-y) $(qobject-obj-y)
 
 qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx
 	$(call quiet-command,sh $(SRC_PATH)/hxtool -h < $< > $@,"  GEN   $@")
@@ -133,6 +141,7 @@ clean:
 	rm -f *.o *.d *.a $(TOOLS) TAGS cscope.* *.pod *~ */*~
 	rm -f slirp/*.o slirp/*.d audio/*.o audio/*.d block/*.o block/*.d net/*.o net/*.d fsdev/*.o fsdev/*.d ui/*.o ui/*.d
 	rm -f qemu-img-cmds.h
+	rm -f trace.c trace.h
 	$(MAKE) -C tests clean
 	for d in $(ALL_SUBDIRS) libhw32 libhw64 libuser libdis libdis-user; do \
 	if test -d $$d; then $(MAKE) -C $$d $@ || exit 1; fi; \