¡@

Home 

OpenStack Study: loop.py

OpenStack Index

**** CubicPower OpenStack Study ****

# Copyright 2011 Red Hat, Inc.

#

# 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.

"""Support for mounting images with the loop device."""

from nova.openstack.common.gettextutils import _

from nova.openstack.common import log as logging

from nova import utils

from nova.virt.disk.mount import api

LOG = logging.getLogger(__name__)

**** CubicPower OpenStack Study ****

class LoopMount(api.Mount):

"""loop back support for raw images."""

mode = 'loop'

**** CubicPower OpenStack Study ****

    def _inner_get_dev(self):

        out, err = utils.trycmd('losetup', '--find', '--show', self.image,

                                run_as_root=True)

        if err:

            self.error = _('Could not attach image to loopback: %s') % err

            LOG.info(_('Loop mount error: %s'), self.error)

            self.linked = False

            self.device = None

            return False

        self.device = out.strip()

        LOG.debug(_("Got loop device %s"), self.device)

        self.linked = True

        return True

**** CubicPower OpenStack Study ****

    def get_dev(self):

        # NOTE(mikal): the retry is required here in case we are low on loop

        # devices. Note however that modern kernels will use more loop devices

        # if they exist. If you're seeing lots of retries, consider adding

        # more devices.

        return self._get_dev_retry_helper()

**** CubicPower OpenStack Study ****

    def unget_dev(self):

        if not self.linked:

            return

        # NOTE(mikal): On some kernels, losetup -d will intermittently fail,

        # thus leaking a loop device unless the losetup --detach is retried:

        # https://lkml.org/lkml/2012/9/28/62

        LOG.debug(_("Release loop device %s"), self.device)

        utils.execute('losetup', '--detach', self.device, run_as_root=True,

                      attempts=3)

        self.linked = False

        self.device = None