89 lines
2.6 KiB
Python
89 lines
2.6 KiB
Python
# 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']
|
|
output = check_output(cmd)
|
|
if six.PY3:
|
|
output = output.decode('utf-8')
|
|
devs = [d.strip().split(' ') for d in output.splitlines() if d != '']
|
|
for dev, _, f in devs:
|
|
loopbacks[dev.replace(':', '')] = re.search(r'\((\S+)\)', 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, "")
|