[Qemu-devel] [PATCH 1/7] trace: Add trace-events file for declaring trace events

[Stefan Hajnoczi]

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.

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
v2:
 * Use "$source_path/tracetool" in ./configure
 * Include qemu-common.h in trace.h so common types are available

 .gitignore      |    2 +
 Makefile        |   17 ++++-
 Makefile.objs   |    5 ++
 Makefile.target |    1 +
 configure       |   19 ++++++
 trace-events    |   24 ++++++++
 tracetool       |  165 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 229 insertions(+), 4 deletions(-)
 create mode 100644 trace-events
 create mode 100755 tracetool

diff --git a/.gitignore b/.gitignore
index fdfe2f0..4644557 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,8 @@ config-devices.*
 config-all-devices.*
 config-host.*
 config-target.*
+trace.h
+trace.c
 *-softmmu
 *-darwin-user
 *-linux-user
diff --git a/Makefile b/Makefile
index 7986bf6..a9f79a9 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.
@@ -130,16 +130,24 @@ bt-host.o: QEMU_CFLAGS += $(BLUEZ_CFLAGS)
 
 iov.o: iov.c iov.h
 
+trace.h: trace-events
+       $(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -h < 
$< > $@,"  GEN   $@")
+
+trace.c: trace-events
+       $(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -c < 
$< > $@,"  GEN   $@")
+
+trace.o: trace.c
+
 ######################################################################
 
 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   $@")
@@ -157,6 +165,7 @@ 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
        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 $@ || exit 1; fi; \
diff --git a/Makefile.objs b/Makefile.objs
index 1a942e5..20e709e 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -251,6 +251,11 @@ libdis-$(CONFIG_S390_DIS) += s390-dis.o
 libdis-$(CONFIG_SH4_DIS) += sh4-dis.o
 libdis-$(CONFIG_SPARC_DIS) += sparc-dis.o
 
+######################################################################
+# trace
+
+trace-obj-y = trace.o
+
 vl.o: QEMU_CFLAGS+=$(GPROF_CFLAGS)
 
 vl.o: QEMU_CFLAGS+=$(SDL_CFLAGS)
diff --git a/Makefile.target b/Makefile.target
index fda5bf3..8f7b564 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -293,6 +293,7 @@ $(obj-y) $(obj-$(TARGET_BASE_ARCH)-y): $(GENERATED_HEADERS)
 
 obj-y += $(addprefix ../, $(common-obj-y))
 obj-y += $(addprefix ../libdis/, $(libdis-y))
+obj-y += $(addprefix ../, $(trace-obj-y))
 obj-y += $(libobj-y)
 obj-y += $(addprefix $(HWDIR)/, $(hw-obj-y))
 
diff --git a/configure b/configure
index 3cd2c5f..e94e113 100755
--- a/configure
+++ b/configure
@@ -299,6 +299,7 @@ pkgversion=""
 check_utests="no"
 user_pie="no"
 zero_malloc=""
+trace_backend="nop"
 
 # OS specific
 if check_define __linux__ ; then
@@ -494,6 +495,8 @@ for opt do
   ;;
   --target-list=*) target_list="$optarg"
   ;;
+  --trace-backend=*) trace_backend="$optarg"
+  ;;
   --enable-gprof) gprof="yes"
   ;;
   --static)
@@ -826,6 +829,7 @@ echo "  --enable-docs            enable documentation build"
 echo "  --disable-docs           disable documentation build"
 echo "  --disable-vhost-net      disable vhost-net acceleration support"
 echo "  --enable-vhost-net       enable vhost-net acceleration support"
+echo "  --trace-backend=B        Trace backend nop"
 echo ""
 echo "NOTE: The object files are built at the place where configure is 
launched"
 exit 1
@@ -1914,6 +1918,18 @@ if compile_prog "" "" ; then
     fdatasync=yes
 fi
 
+##########################################
+# check if trace backend exists
+
+sh "$source_path/tracetool" "--$trace_backend" --check-backend > /dev/null 2> 
/dev/null
+if test "$?" -ne 0 ; then
+  echo
+  echo "Error: invalid trace backend"
+  echo "Please choose a supported trace backend."
+  echo
+  exit 1
+fi
+
 # End of CC checks
 # After here, no more $cc or $ld runs
 
@@ -2041,6 +2057,7 @@ echo "preadv support    $preadv"
 echo "fdatasync         $fdatasync"
 echo "uuid support      $uuid"
 echo "vhost-net support $vhost_net"
+echo "Trace backend     $trace_backend"
 
 if test $sdl_too_old = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -2284,6 +2301,8 @@ bsd)
 ;;
 esac
 
+echo "TRACE_BACKEND=$trace_backend" >> $config_host_mak
+
 tools=
 if test `expr "$target_list" : ".*softmmu.*"` != 0 ; then
   tools="qemu-img\$(EXESUF) qemu-io\$(EXESUF) $tools"
diff --git a/trace-events b/trace-events
new file mode 100644
index 0000000..a37d3cc
--- /dev/null
+++ b/trace-events
@@ -0,0 +1,24 @@
+# Trace events for debugging and performance instrumentation
+#
+# This file is processed by the tracetool script during the build.
+#
+# To add a new trace event:
+#
+# 1. Choose a name for the trace event.  Declare its arguments and format
+#    string.
+#
+# 2. Call the trace event from code using trace_##name, e.g. multiwrite_cb() ->
+#    trace_multiwrite_cb().  The source file must #include "trace.h".
+#
+# Format of a trace event:
+#
+# <name>(<type1> <arg1>[, <type2> <arg2>] ...) "<format-string>"
+#
+# Example: qemu_malloc(size_t size) "size %zu"
+#
+# The <name> must be a valid as a C function name.
+#
+# Types should be standard C types.  Use void * for pointers because the trace
+# system may not have the necessary headers included.
+#
+# The <format-string> should be a sprintf()-compatible format string.
diff --git a/tracetool b/tracetool
new file mode 100755
index 0000000..766a9ba
--- /dev/null
+++ b/tracetool
@@ -0,0 +1,165 @@
+#!/bin/sh
+
+usage()
+{
+    cat >&2 <<EOF
+usage: $0 --nop [-h | -c]
+Generate tracing code for a file on stdin.
+
+Backends:
+  --nop Tracing disabled
+
+Output formats:
+  -h    Generate .h file
+  -c    Generate .c file
+EOF
+    exit 1
+}
+
+# Get the name of a trace event
+get_name()
+{
+    echo ${1%%(*}
+}
+
+# Get the argument list of a trace event, including types and names
+get_args()
+{
+    local args
+    args=${1#*(}
+    args=${args%)*}
+    echo "$args"
+}
+
+# Get the argument name list of a trace event
+get_argnames()
+{
+    local first field name
+    for field in $(get_args "$1"); do
+        # Drop pointer star
+        field=${field#\*}
+
+        # Only argument names have commas at the end
+        name=${field%,}
+        test "$field" = "$name" && continue
+
+        echo -n "$name, "
+    done
+    echo -n "$name"
+}
+
+# Get the format string for a trace event
+get_fmt()
+{
+    local fmt
+    fmt=${1#*\"}
+    fmt=${fmt%\"*}
+    echo "$fmt"
+}
+
+warn_autogen_c()
+{
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+}
+
+warn_autogen_h()
+{
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+}
+
+linetoh_begin_nop()
+{
+    return
+}
+
+linetoh_nop()
+{
+    local name args
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+
+    # Define an empty function for the trace event
+    cat <<EOF
+static inline void trace_$name($args)
+{
+}
+EOF
+}
+
+linetoh_end_nop()
+{
+    return
+}
+
+linetoc_begin_nop()
+{
+    return
+}
+
+linetoc_nop()
+{
+    # No need for function definitions in nop backend
+    return
+}
+
+linetoc_end_nop()
+{
+    return
+}
+
+# Process stdin by calling begin, line, and end functions for the backend
+convert()
+{
+    local begin process_line end
+    begin="lineto$1_begin_$backend"
+    process_line="lineto$1_$backend"
+    end="lineto$1_end_$backend"
+
+    warn_autogen_$1
+    "$begin"
+
+    while read -r str; do
+        # Skip comments and empty lines
+        str=${str%%#*}
+        test -z "$str" && continue
+
+        echo
+        "$process_line" "$str"
+    done
+
+    echo
+    "$end"
+}
+
+tracetoh()
+{
+    cat <<EOF
+#ifndef TRACE_H
+#define TRACE_H
+
+#include "qemu-common.h"
+EOF
+    convert h
+    echo "#endif /* TRACE_H */"
+}
+
+tracetoc()
+{
+    convert c
+}
+
+# Choose backend
+case "$1" in
+"--nop") backend="${1#--}" ;;
+*) usage ;;
+esac
+shift
+
+case "$1" in
+"-h") tracetoh ;;
+"-c") tracetoc ;;
+"--check-backend") exit 0 ;; # used by ./configure to test for backend
+*) usage ;;
+esac
+
+exit 0
-- 
1.7.1