trace: include filename when printing parser error messages

Improves error messages from:

  ValueError: Error on line 72: need more than 1 value to unpack

To

  ValueError: Error at /home/berrange/src/virt/qemu/trace-events:72:
    need more than 1 value to unpack

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180306154650.24075-1-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/simpletrace.py

@@ -168,7 +168,7 @@ def end(self):
 def process(events, log, analyzer, read_header=True):
     """Invoke an analyzer on each event in a log."""
     if isinstance(events, str):
-        events = read_events(open(events, 'r'))
+        events = read_events(open(events, 'r'), events)
     if isinstance(log, str):
         log = open(log, 'rb')
 
@@ -233,7 +233,7 @@ def run(analyzer):
                          '<trace-file>\n' % sys.argv[0])
         sys.exit(1)
 
-    events = read_events(open(sys.argv[1], 'r'))
+    events = read_events(open(sys.argv[1], 'r'), sys.argv[1])
     process(events, sys.argv[2], analyzer, read_header=read_header)
 
 if __name__ == '__main__':

scripts/tracetool.py

@@ -142,7 +142,7 @@ def main(args):
     events = []
     for arg in args:
         with open(arg, "r") as fh:
-            events.extend(tracetool.read_events(fh))
+            events.extend(tracetool.read_events(fh, arg))
 
     try:
         tracetool.generate(events, arg_group, arg_format, arg_backends,

scripts/tracetool/__init__.py

@@ -291,13 +291,15 @@ def transform(self, *trans):
                      self)
 
 
-def read_events(fobj):
+def read_events(fobj, fname):
     """Generate the output for the given (format, backends) pair.
 
     Parameters
     ----------
     fobj : file
         Event description file.
+    fname : str
+        Name of event file
 
     Returns a list of Event objects
     """
@@ -312,7 +314,7 @@ def read_events(fobj):
         try:
             event = Event.build(line)
         except ValueError as e:
-            arg0 = 'Error on line %d: %s' % (lineno, e.args[0])
+            arg0 = 'Error at %s:%d: %s' % (fname, lineno, e.args[0])
             e.args = (arg0,) + e.args[1:]
             raise