[Xen-devel] [PULL 2/7] trace: avoid SystemTap dtrace(1) warnings on empty files

[Stefan Hajnoczi <stefanha@xxxxxxxxxx>]

target/hppa/trace-events only contains disabled events, resulting in a
trace-dtrace.dtrace file that says "provider qemu {}".  SystemTap's
dtrace(1) tool prints a warning when processing this input file.

This patch avoids the error by emitting an empty file instead of
"provider qemu {}" when there are no enabled trace events.

Fixes: 23c3d569f44284066714ff7c46bc4f19e630583f ("target/hppa: add TLB trace 
events")
Reported-by: Markus Armbruster <armbru@xxxxxxxxxx>
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Reviewed-by: Markus Armbruster <armbru@xxxxxxxxxx>
Reviewed-by: Liam Merwick <liam.merwick@xxxxxxxxxx>
Message-id: 20190321170831.6539-3-stefanha@xxxxxxxxxx
Message-Id: <20190321170831.6539-3-stefanha@xxxxxxxxxx>
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
 scripts/tracetool/format/d.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/scripts/tracetool/format/d.py b/scripts/tracetool/format/d.py
index 78397c24d2..c7cb2a93a6 100644
--- a/scripts/tracetool/format/d.py
+++ b/scripts/tracetool/format/d.py
@@ -33,6 +33,11 @@ def generate(events, backend, group):
     events = [e for e in events
               if "disable" not in e.properties]
 
+    # SystemTap's dtrace(1) warns about empty "provider qemu {}" but is happy
+    # with an empty file.  Avoid the warning.
+    if not events:
+        return
+
     out('/* This file is autogenerated by tracetool, do not edit. */'
         '',
         'provider qemu {')
-- 
2.20.1


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