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# 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)
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, "")
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