[Qemu-trivial] [PATCH] simpletrace: Improve the error message if event is not declared

[Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>]

Today, if we use a trace-event file which does not declare an event
existing in the log file we'll get the following error:

$ scripts/simpletrace.py trace-events trace-68508
Traceback (most recent call last):
  File "scripts/simpletrace.py", line 242, in <module>
    run(Formatter())
  File "scripts/simpletrace.py", line 217, in run
    process(events, sys.argv[2], analyzer, read_header=read_header)
  File "scripts/simpletrace.py", line 192, in process
    for rec in read_trace_records(edict, log):
  File "scripts/simpletrace.py", line 107, in read_trace_records
    rec = read_record(edict, idtoname, fobj)
  File "scripts/simpletrace.py", line 71, in read_record
    return get_record(edict, idtoname, rechdr, fobj)
  File "scripts/simpletrace.py", line 45, in get_record
    event = edict[name]
KeyError: 'qemu_mutex_locked'

This patch improves this error by adding a hint instead of just that
KeyError log:

$ scripts/simpletrace.py trace-events trace-68508
'qemu_mutex_locked' event is logged but is not declared in the trace
events file, try using trace-events-all instead.

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
---
 scripts/simpletrace.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/scripts/simpletrace.py b/scripts/simpletrace.py
index d60b3a0..f1be6e4 100755
--- a/scripts/simpletrace.py
+++ b/scripts/simpletrace.py
@@ -42,7 +42,15 @@ def get_record(edict, idtoname, rechdr, fobj):
         event_id = rechdr[0]
         name = idtoname[event_id]
         rec = (name, rechdr[1], rechdr[3])
-        event = edict[name]
+        try:
+            event = edict[name]
+        except KeyError, e:
+            import sys
+            sys.stderr.write('%s event is logged but is not declared ' \
+                             'in the trace events file, try using ' \
+                             'trace-events-all instead.\n' % str(e))
+            sys.exit(1)
+
         for type, name in event.args:
             if is_string(type):
                 l = fobj.read(4)
-- 
2.7.4