Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' into staging

Pull request

v2:
 * Replaced "Launchpad:" tag with "Buglink:" as documented on the SubmitAPatch wiki page [Philippe]

# gpg: Signature made Tue 15 Oct 2019 09:49:05 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/tracing-pull-request:
  trace: avoid "is" with a literal Python 3.8 warnings
  trace: add --group=all to tracing.txt
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

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.

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):