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OpenStack Study: nbd.py**** 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 qemu-nbd.""" import os import random import re import time from oslo.config import cfg 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__) nbd_opts = [ cfg.IntOpt('timeout_nbd', default=10, help='Amount of time, in seconds, to wait for NBD ' 'device start up.'), ] CONF = cfg.CONF CONF.register_opts(nbd_opts) NBD_DEVICE_RE = re.compile('nbd[0-9]+')
**** CubicPower OpenStack Study **** class NbdMount(api.Mount): """qemu-nbd support disk images.""" mode = 'nbd'
**** CubicPower OpenStack Study **** def _detect_nbd_devices(self): """Detect nbd device files.""" return filter(NBD_DEVICE_RE.match, os.listdir('/sys/block/'))
**** CubicPower OpenStack Study **** def _find_unused(self, devices): for device in devices: if not os.path.exists(os.path.join('/sys/block/', device, 'pid')): if not os.path.exists('/var/lock/qemu-nbd-%s' % device): return device else: LOG.error(_('NBD error - previous umount did not cleanup ' '/var/lock/qemu-nbd-%s.'), device) LOG.warn(_('No free nbd devices')) return None
**** CubicPower OpenStack Study **** def _allocate_nbd(self): if not os.path.exists('/sys/block/nbd0'): LOG.error(_('nbd module not loaded')) self.error = _('nbd unavailable: module not loaded') return None devices = self._detect_nbd_devices() random.shuffle(devices) device = self._find_unused(devices) if not device: # really want to log this info, not raise self.error = _('No free nbd devices') return None return os.path.join('/dev', device) @utils.synchronized('nbd-allocation-lock')
**** CubicPower OpenStack Study **** def _inner_get_dev(self): device = self._allocate_nbd() if not device: return False # NOTE(mikal): qemu-nbd will return an error if the device file is # already in use. LOG.debug(_('Get nbd device %(dev)s for %(imgfile)s'), {'dev': device, 'imgfile': self.image}) _out, err = utils.trycmd('qemu-nbd', '-c', device, self.image, run_as_root=True) if err: self.error = _('qemu-nbd error: %s') % err LOG.info(_('NBD mount error: %s'), self.error) return False # NOTE(vish): this forks into another process, so give it a chance # to set up before continuing pidfile = "/sys/block/%s/pid" % os.path.basename(device) for _i in range(CONF.timeout_nbd): if os.path.exists(pidfile): self.device = device break time.sleep(1) else: self.error = _('nbd device %s did not show up') % device LOG.info(_('NBD mount error: %s'), self.error) # Cleanup _out, err = utils.trycmd('qemu-nbd', '-d', device, run_as_root=True) if err: LOG.warn(_('Detaching from erroneous nbd device returned ' 'error: %s'), err) return False self.error = '' self.linked = True return True
**** CubicPower OpenStack Study **** def get_dev(self): """Retry requests for NBD devices.""" return self._get_dev_retry_helper()
**** CubicPower OpenStack Study **** def unget_dev(self): if not self.linked: return LOG.debug(_('Release nbd device %s'), self.device) utils.execute('qemu-nbd', '-d', self.device, run_as_root=True) self.linked = False self.device = None
**** CubicPower OpenStack Study **** def flush_dev(self): """flush NBD block device buffer.""" # Perform an explicit BLKFLSBUF to support older qemu-nbd(s). # Without this flush, when a nbd device gets re-used the # qemu-nbd intermittently hangs. if self.device: utils.execute('blockdev', '--flushbufs', self.device, run_as_root=True)
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