1 files changed, 86 insertions, 0 deletions
diff --git a/charms/trusty/ceilometer-agent/hooks/charmhelpers/contrib/storage/linux/loopback.py b/charms/trusty/ceilometer-agent/hooks/charmhelpers/contrib/storage/linux/loopback.py
new file mode 100644
index 0000000..1d6ae6f
--- /dev/null
+++ b/charms/trusty/ceilometer-agent/hooks/charmhelpers/contrib/storage/linux/loopback.py
@@ -0,0 +1,86 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#  http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import re
+from subprocess import (
+    check_call,
+    check_output,
+)
+
+import six
+
+
+##################################################
+# loopback device helpers.
+##################################################
+def loopback_devices():
+    '''
+    Parse through 'losetup -a' output to determine currently mapped
+    loopback devices. Output is expected to look like:
+
+        /dev/loop0: [0807]:961814 (/tmp/my.img)
+
+    :returns: dict: a dict mapping {loopback_dev: backing_file}
+    '''
+    loopbacks = {}
+    cmd = ['losetup', '-a']
+    devs = [d.strip().split(' ') for d in
+            check_output(cmd).splitlines() if d != '']
+    for dev, _, f in devs:
+        loopbacks[dev.replace(':', '')] = re.search('\((\S+)\)', f).groups()[0]
+    return loopbacks
+
+
+def create_loopback(file_path):
+    '''
+    Create a loopback device for a given backing file.
+
+    :returns: str: Full path to new loopback device (eg, /dev/loop0)
+    '''
+    file_path = os.path.abspath(file_path)
+    check_call(['losetup', '--find', file_path])
+    for d, f in six.iteritems(loopback_devices()):
+        if f == file_path:
+            return d
+
+
+def ensure_loopback_device(path, size):
+    '''
+    Ensure a loopback device exists for a given backing file path and size.
+    If it a loopback device is not mapped to file, a new one will be created.
+
+    TODO: Confirm size of found loopback device.
+
+    :returns: str: Full path to the ensured loopback device (eg, /dev/loop0)
+    '''
+    for d, f in six.iteritems(loopback_devices()):
+        if f == path:
+            return d
+
+    if not os.path.exists(path):
+        cmd = ['truncate', '--size', size, path]
+        check_call(cmd)
+
+    return create_loopback(path)
+
+
+def is_mapped_loopback_device(device):
+    """
+    Checks if a given device name is an existing/mapped loopback device.
+    :param device: str: Full path to the device (eg, /dev/loop1).
+    :returns: str: Path to the backing file if is a loopback device
+    empty string otherwise
+    """
+    return loopback_devices().get(device, "")