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-rw-r--r--docs/devel/tracing.txt3
-rw-r--r--scripts/tracetool/__init__.py4
2 files changed, 4 insertions, 3 deletions
diff --git a/docs/devel/tracing.txt b/docs/devel/tracing.txt
index 8231bbf5d1..8c0376fefa 100644
--- a/docs/devel/tracing.txt
+++ b/docs/devel/tracing.txt
@@ -317,7 +317,8 @@ probes:
                          --binary path/to/qemu-binary \
                          --target-type system \
                          --target-name x86_64 \
-                         <trace-events-all >qemu.stp
+                         --group=all \
+                         trace-events-all >qemu.stp
 
 To facilitate simple usage of systemtap where there merely needs to be printf
 logging of certain probes, a helper script "qemu-trace-stap" is provided.
diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
index 04279fa62e..44c118bc2a 100644
--- a/scripts/tracetool/__init__.py
+++ b/scripts/tracetool/__init__.py
@@ -456,12 +456,12 @@ def generate(events, group, format, backends,
     import tracetool
 
     format = str(format)
-    if len(format) is 0:
+    if len(format) == 0:
         raise TracetoolError("format not set")
     if not tracetool.format.exists(format):
         raise TracetoolError("unknown format: %s" % format)
 
-    if len(backends) is 0:
+    if len(backends) == 0:
         raise TracetoolError("no backends specified")
     for backend in backends:
         if not tracetool.backend.exists(backend):