1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
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, "")
|
