[Qemu-devel] [PATCH 3/5] trace: Add LTTng Userspace Tracer backend

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

This patch adds LTTng Userspace Tracer (UST) backend support.  The UST
system requires no kernel support but libust and liburcu must be
installed.

$ ./configure --trace-backend ust
$ make

Start the UST daemon:
$ ustd &

List available tracepoints and enable some:
$ ustctl --list-markers $(pgrep qemu)
[...]
{PID: 5458, channel/marker: ust/paio_submit, state: 0, fmt: "acb %p
opaque %p sector_num %lu nb_sectors %lu type %lu" 0x4b32ba}
$ ustctl --enable-marker "ust/paio_submit" $(pgrep qemu)

Run the trace:
$ ustctl --create-trace $(pgrep qemu)
$ ustctl --start-trace $(pgrep qemu)
[...]
$ ustctl --stop-trace $(pgrep qemu)
$ ustctl --destroy-trace $(pgrep qemu)

Trace results can be viewed using lttv-gui.

More information about UST:
http://lttng.org/ust

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
I wrote this as part of trying out UST.  Although UST is promising, the
usability is poor at the moment.

The dependencies include the lttv trace viewer which I had to build from source
(and it required a makefile tweak to build).  Luckily libust, liburcu, and
ust-bin are packaged on my distro.

Error messages are periodically printed by the UST code when running QEMU.  I
haven't investigated but this is may be due to signals interrupting UST's
thread in poll().

Finally, the UST header files include some userspace ported kernel
infrastructure and pollute the namespace.  I had to add some #undefs to get
QEMU to build after including UST headers.

I don't see LTTng UST as a default option at the moment.  Hopefully this will
change in the future.

 configure |    5 +++-
 tracetool |   77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index d599879..307dbcb 100755
--- a/configure
+++ b/configure
@@ -829,7 +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 simple"
+echo "  --trace-backend=B        Trace backend nop simple ust"
 echo ""
 echo "NOTE: The object files are built at the place where configure is launched"
 exit 1
@@ -2302,6 +2302,9 @@ bsd)
 esac
 
 echo "TRACE_BACKEND=$trace_backend" >> $config_host_mak
+if test "$trace_backend" = "ust"; then
+  LIBS="-lust $LIBS"
+fi
 
 tools=
 if test `expr "$target_list" : ".*softmmu.*"` != 0 ; then
diff --git a/tracetool b/tracetool
index bcd163e..72beb20 100755
--- a/tracetool
+++ b/tracetool
@@ -3,12 +3,13 @@
 usage()
 {
     cat >&2 <<EOF
-usage: $0 [--nop | --simple] [-h | -c | --py]
+usage: $0 [--nop | --simple | --ust] [-h | -c | --py]
 Generate tracing code for a file on stdin.
 
 Backends:
   --nop     Tracing disabled
   --simple  Simple built-in backend
+  --ust     LTTng User Space Tracing backend
 
 Output formats:
   -h    Generate .h file
@@ -220,6 +221,78 @@ linetopy_end_simple()
     echo "}"
 }
 
+linetoh_begin_ust()
+{
+    echo "#include <ust/tracepoint.h>"
+}
+
+linetoh_ust()
+{
+    local name args argnames
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1")
+
+    cat <<EOF
+DECLARE_TRACE(ust_$name, TPPROTO($args), TPARGS($argnames));
+#define trace_$name trace_ust_$name
+EOF
+}
+
+linetoh_end_ust()
+{
+    # Clean up after UST headers which pollute the namespace
+    cat <<EOF
+#undef mutex_lock
+#undef mutex_unlock
+EOF
+}
+
+linetoc_begin_ust()
+{
+    cat <<EOF
+#include <ust/marker.h>
+#include "trace.h"
+EOF
+}
+
+linetoc_ust()
+{
+    local name args argnames fmt
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1")
+    fmt=$(get_fmt "$1")
+
+    cat <<EOF
+DEFINE_TRACE(ust_$name);
+
+static void ust_${name}_probe($args)
+{
+    trace_mark(ust, $name, "$fmt", $argnames);
+}
+EOF
+
+    # Collect names for later
+    names="$names $name"
+}
+
+linetoc_end_ust()
+{
+    cat <<EOF
+static void __attribute__((constructor)) trace_init(void)
+{
+EOF
+
+    for name in $names; do
+        cat <<EOF
+    register_trace_ust_$name(ust_${name}_probe);
+EOF
+    done
+
+    echo "}"
+}
+
 # Process stdin by calling begin, line, and end functions for the backend
 convert()
 {
@@ -267,7 +340,7 @@ tracetopy()
 
 # Choose backend
 case "$1" in
-"--nop" | "--simple") backend="${1#--}" ;;
+"--nop" | "--simple" | "--ust") backend="${1#--}" ;;
 *) usage ;;
 esac
 shift
-- 
1.7.1