diskstat: really discover devs when devices is missing

hashar · hashar · commit e9a4930f9b47 · 2013-10-23T11:51:49.000+02:00
The diskstat plugin is supposed, by default, to monitor any entry not
containing a number under /proc/diskstat. Hence I created a very basic
diskstat.pyconf, roughly:

 modules {
   module {
     name = 'diskstat'
     language = 'python'
   }
 }

The metric_init would get() 'devices' from the list of parameters which
set it to None.  The partition discovery is only done when 'devices' is
an empty string so the rest of the code would try to interact with None.
That eventually leads to:

 diskstat.py", line 181, in get_partitions
    for dev in out.split():
 AttributeError: 'NoneType' object has no attribute 'split'

The fix is to make DEVICES to default to None and change the boolean
logic:

 - if DEVICES != '':
 + if DEVICES is not None:

To be ultra explicit to python newbie, we might even want to update the
get() call to: get('devices', None), but I dont think that is really
needed.
diff --git a/diskstat/python_modules/diskstat.py b/diskstat/python_modules/diskstat.py
@@ -6,6 +6,10 @@
 ###    more information on these values, look in the Linux kernel
 ###    documentation for "I/O statistics fields".
 ###
+###    By default, the script would monitor any entry listed under
+###    /proc/diskstats that is not containing a number. Override it by passing
+###    a list of devices in the 'devices' parameter.
+###
 ###    This script has the option of explicitly setting which devices
 ###    to check using the "devices" option in your configuration. If
 ###    you set this value, it will invalidate the MIN_DISK_SIZE and
@@ -58,7 +62,9 @@
 
 # 5 GB
 MIN_DISK_SIZE = 5242880
-DEVICES = ''
+# Set to None to trigger disk discovery under /proc/diskstats
+# Pass a 'devices' parameter to explicitly list disks to monitor
+DEVICES = None
 IGNORE_DEV = 'dm-|loop|drbd'
 
 PARTITIONS_FILE = '/proc/partitions'
@@ -162,7 +168,7 @@ def get_partitions():
 	logging.debug('getting partitions')
 	global PARTITIONS
 
-	if DEVICES != '':
+	if DEVICES is not None:
 		# Explicit device list has been set
 		logging.debug(' DEVICES has already been set')
 		out = DEVICES
@@ -179,7 +185,7 @@ def get_partitions():
 			return p.returncode
 
 	for dev in out.split():
-		if DEVICES != '':
+		if DEVICES is not None:
 			# Explicit device list has been set
 			PARTITIONS.append(dev)
 		else:		
