Add some more checks to engine creation

Add a field called enabled in the engine cfg file that keeps track of
files. This can be used to keep track of stopped engines, and
monitored using watchdog/similar. Also added some more checks at
engine creation time.

Partially Closes-bug:1309406
Change-Id: I1c365c2c438e6ed0a44413e1d09c69d3fab7ab7b

entropy/__main__.py

@@ -90,18 +90,33 @@ def start_engine(args):
     if not (args.name and args.engine_cfg):
         LOG.error('Need name and engine cfg')
         return
-    cfg_data = dict(utils.load_yaml(args.engine_cfg))[args.name]
+    utils.create_files([engine_cfg])
-    cfg = {
+    if args.purge:
-        args.name: {
+        utils.purge_disabled(engine_cfg)
-            'cfg': os.path.join(os.getcwd(), args.engine_cfg),
+    if utils.check_exists_and_enabled(args.name, engine_cfg):
-            'pid': os.getpid(),
+        LOG.error("An engine of the same name %s is already "
-            'backend': cfg_data['backend']
+                  "registered and running", args.name)
+        return
+    if utils.check_exists_and_disabled(args.name, engine_cfg):
+        LOG.error("And engine of the same name %s is already "
+                  "registered, but disabled. Run with purge?", args.name)
+        return
+    try:
+        cfg_data = dict(utils.load_yaml(args.engine_cfg))[args.name]
+        cfg = {
+            args.name: {
+                'cfg': os.path.join(os.getcwd(), args.engine_cfg),
+                'pid': os.getpid(),
+                'backend': cfg_data['backend']
+            }
         }
-    }
+        utils.write_yaml(cfg, engine_cfg)
-    utils.write_yaml(cfg, engine_cfg)
+        LOG.info('Added %s to engine cfg', args.name)
-    LOG.info('Added %s to engine cfg', args.name)
+        entropy_engine = Engine(args.name, **cfg_data)
-    entropy_engine = Engine(args.name, **cfg_data)
+        entropy_engine.run()
-    entropy_engine.run()
+    except Exception:
+        LOG.exception("Could not start engine %s", args.name)
+        return
 
 
 def parse():

entropy/utils.py

@@ -106,11 +106,47 @@ class WatchdogHandler(FileSystemEventHandler):
 def watch_dir_for_change(dir_to_watch, event_fn):
     event_handler = WatchdogHandler(event_fn)
     observer = Observer()
-    observer.schedule(event_handler, path=dir_to_watch, recursive=True)
+    observer.schedule(event_handler, path=dir_to_watch)
     observer.start()
     return observer
 
 
+def check_exists_and_enabled(name, cfg_file):
+    engines = load_yaml(cfg_file)
+    return engines and name in engines and engines[name]['enabled']
+
+
+def check_exists_and_disabled(name, cfg_file):
+    engines = load_yaml(cfg_file)
+    return engines and name in engines and not engines[name]['enabled']
+
+
+def purge_disabled(cfg_file):
+    engines = load_yaml(cfg_file)
+    final_engines = {}
+    if not engines:
+        return
+    for engine in engines:
+        if engines[engine]['enabled']:
+            final_engines[engine] = engines[engine]
+    if final_engines:
+        write_yaml(final_engines, cfg_file, append=False)
+    else:
+        with open(cfg_file, 'w'):
+            pass
+
+
+def disable_engine(name, cfg_file):
+    engines = load_yaml(cfg_file)
+    if not engines:
+        raise Exception("No engines at all!")
+    if name not in engines:
+        raise Exception("No such engine!")
+    engines[name]['enabled'] = False
+    write_yaml(engines, cfg_file, append=False)
+    return engines[name]['pid']
+
+
 def reset_logger(log):
     if not log:
         return
@@ -123,8 +159,9 @@ def reset_logger(log):
     log.addHandler(logging.NullHandler())
 
 
-def write_yaml(data, filename):
+def write_yaml(data, filename, append=True):
-    with open(filename, "a") as cfg_file:
+    mode = "a" if append else "w"
+    with open(filename, mode) as cfg_file:
         cfg_file.write(yaml.safe_dump(data,
                                       default_flow_style=False,
                                       canonical=False))