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