79 lines
2.3 KiB
Python
79 lines
2.3 KiB
Python
# Copyright 2014-2015 Canonical Limited.
|
|
#
|
|
# This file is part of charm-helpers.
|
|
#
|
|
# charm-helpers is free software: you can redistribute it and/or modify
|
|
# it under the terms of the GNU Lesser General Public License version 3 as
|
|
# published by the Free Software Foundation.
|
|
#
|
|
# charm-helpers is distributed in the hope that it will be useful,
|
|
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
# GNU Lesser General Public License for more details.
|
|
#
|
|
# You should have received a copy of the GNU Lesser General Public License
|
|
# along with charm-helpers. If not, see <http://www.gnu.org/licenses/>.
|
|
|
|
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)
|