trace: introduce a formal group name for trace events

The declarations in the generated-tracers.h file are
assuming there's only ever going to be one instance
of this header, as they are not namespaced. When we
have one header per event group, if a single source
file needs to include multiple sets of trace events,
the symbols will all clash.

This change thus introduces a '--group NAME' arg to the
'tracetool' program. This will cause all the symbols in
the generated header files to be given a unique namespace.

If no group is given, the group name 'common' is used,
which is suitable for the current usage where there is
only one global trace-events file used for code generation.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
Message-id: 1475588159-30598-21-git-send-email-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/backend/log.py

@@ -19,12 +19,12 @@ from tracetool import out
 PUBLIC = True
 
 
-def generate_h_begin(events):
+def generate_h_begin(events, group):
     out('#include "qemu/log.h"',
         '')
 
 
-def generate_h(event):
+def generate_h(event, group):
     argnames = ", ".join(event.args.names())
     if len(event.args) > 0:
         argnames = ", " + argnames