From 658005a178202c691e9dec4dfc9a9e91ecb62420 Mon Sep 17 00:00:00 2001
From: Patrick Bellasi <patrick.bellasi@arm.com>
Date: Tue, 26 Apr 2016 15:26:44 +0100
Subject: [PATCH] cgroups: properly format attributes path and check for being
 supported

CGroups controller can be mounted by specifying a "noprefix" option,
in which case attribute names are named as:
   <mountpoint>/<attribute_name>
instead of the (more recent) naming schema using:
   <mountpoint>/<contoller_name>.<attribute_name>

For example, Android uses the old format for backward compatibility
with user-space. Thus, it's possible in general to work on a target
system where some controller are mounted "noprefix" while others not.

This patchset adds a set of updates which allows to use the proper
attributes naming schema based on how the controller has been mounted.

This patch makes use of the Controller::_noprefix option to properly
build the attribute path. It adds also a check which reports a more
clear error in case an attribute is set which is not provided by the
controller.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
---
 devlib/module/cgroups.py | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/devlib/module/cgroups.py b/devlib/module/cgroups.py
index 5f87ee7..43d23bb 100644
--- a/devlib/module/cgroups.py
+++ b/devlib/module/cgroups.py
@@ -189,14 +189,25 @@ class CGroup(object):
             if isiterable(attrs[idx]):
                 attrs[idx] = list_to_ranges(attrs[idx])
             # Build attribute path
-            path = '{}.{}'.format(self.controller.kind, idx)
-            path = self.target.path.join(self.directory, path)
+            if self.controller._noprefix:
+                attr_name = '{}'.format(idx)
+            else:
+                attr_name = '{}.{}'.format(self.controller.kind, idx)
+            path = self.target.path.join(self.directory, attr_name)
 
             self.logger.debug('Set attribute [%s] to: %s"',
                     path, attrs[idx])
 
             # Set the attribute value
-            self.target.write_value(path, attrs[idx])
+            try:
+                self.target.write_value(path, attrs[idx])
+            except TargetError:
+                # Check if the error is due to a non-existing attribute
+                attrs = self.get()
+                if idx not in attrs:
+                    raise ValueError('Controller [{}] does not provide attribute [{}]'\
+                                     .format(self.controller.kind, attr_name))
+                raise
 
     def get_tasks(self):
         task_ids = self.target.read_value(self.tasks_file).split()