configuration: add logging_levels section

Allow to configure the logging-levels of various loggers by adding a new
section `logging_levels` to the configuration file. Each entry in that
section configures the logging-level of one logger / channel.

README.md

@@ -113,6 +113,9 @@ collector_opts:
     blacklist:
       - docker0
       - lo
+logging_levels:
+  root: INFO
+  foomodule.barcollector: WARNING
 ```
 
 ### Start-up Configuration

p3.yml

@@ -9,3 +9,5 @@ collector_opts:
     blacklist:
       - docker0
       - lo
+logging_levels:
+  root: INFO

p3exporter/__init__.py

@@ -3,7 +3,7 @@
 from wsgiref.simple_server import make_server
 
 import yaml
-import logging
+import logging.config
 import os
 import signal
 import sys
@@ -41,6 +41,13 @@ def main():
     with open(args.config, 'r') as config_file:
         cfg = yaml.load(config_file, Loader=yaml.SafeLoader)
     collector_config = CollectorConfig(**cfg)
+    if type(cfg.get('logging_levels')) == dict:
+        levels = cfg['logging_levels']
+        loggers = {k: {'level': v} for k, v in levels.items()}
+        logging.config.dictConfig({
+            'version': 1,
+            'loggers': loggers,
+        })
 
     Collector(collector_config)