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path: root/nova/virt/disk/mount/api.py
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# 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 virtual image files."""

import os
import time

from oslo_log import log as logging
from oslo_service import loopingcall
from oslo_utils import importutils

from nova import exception
from nova.i18n import _
import nova.privsep.fs
from nova.virt.image import model as imgmodel

LOG = logging.getLogger(__name__)

MAX_DEVICE_WAIT = 30
MAX_FILE_CHECKS = 6
FILE_CHECK_INTERVAL = 0.25


class Mount(object):
    """Standard mounting operations, that can be overridden by subclasses.

    The basic device operations provided are get, map and mount,
    to be called in that order.
    """

    mode = None  # to be overridden in subclasses

    @staticmethod
    def instance_for_format(image, mountdir, partition):
        """Get a Mount instance for the image type

        :param image: instance of nova.virt.image.model.Image
        :param mountdir: path to mount the image at
        :param partition: partition number to mount
        """
        LOG.debug("Instance for format image=%(image)s "
                  "mountdir=%(mountdir)s partition=%(partition)s",
                  {'image': image, 'mountdir': mountdir,
                   'partition': partition})

        if isinstance(image, imgmodel.LocalFileImage):
            if image.format == imgmodel.FORMAT_RAW:
                LOG.debug("Using LoopMount")
                return importutils.import_object(
                    "nova.virt.disk.mount.loop.LoopMount",
                    image, mountdir, partition)
            else:
                LOG.debug("Using NbdMount")
                return importutils.import_object(
                    "nova.virt.disk.mount.nbd.NbdMount",
                    image, mountdir, partition)
        elif isinstance(image, imgmodel.LocalBlockImage):
            LOG.debug("Using BlockMount")
            return importutils.import_object(
                    "nova.virt.disk.mount.block.BlockMount",
                    image, mountdir, partition)
        else:
            # TODO(berrange) We could mount RBDImage directly
            # using kernel RBD block dev support.
            #
            # This is left as an enhancement for future
            # motivated developers todo, since raising
            # an exception is on par with what this
            # code did historically
            raise exception.UnsupportedImageModel(
                image.__class__.__name__)

    @staticmethod
    def instance_for_device(image, mountdir, partition, device):
        """Get a Mount instance for the device type

        :param image: instance of nova.virt.image.model.Image
        :param mountdir: path to mount the image at
        :param partition: partition number to mount
        :param device: mounted device path
        """

        LOG.debug("Instance for device image=%(image)s "
                  "mountdir=%(mountdir)s partition=%(partition)s "
                  "device=%(device)s",
                  {'image': image, 'mountdir': mountdir,
                   'partition': partition, 'device': device})

        if "loop" in device:
            LOG.debug("Using LoopMount")
            return importutils.import_object(
                "nova.virt.disk.mount.loop.LoopMount",
                image, mountdir, partition, device)
        elif "nbd" in device:
            LOG.debug("Using NbdMount")
            return importutils.import_object(
                "nova.virt.disk.mount.nbd.NbdMount",
                image, mountdir, partition, device)
        else:
            LOG.debug("Using BlockMount")
            return importutils.import_object(
                "nova.virt.disk.mount.block.BlockMount",
                image, mountdir, partition, device)

    def __init__(self, image, mount_dir, partition=None, device=None):
        """Create a new Mount instance

        :param image: instance of nova.virt.image.model.Image
        :param mount_dir: path to mount the image at
        :param partition: partition number to mount
        :param device: mounted device path
        """

        # Input
        self.image = image
        self.partition = partition
        self.mount_dir = mount_dir

        # Output
        self.error = ""

        # Internal
        self.linked = self.mapped = self.mounted = self.automapped = False
        self.device = self.mapped_device = device

        # Reset to mounted dir if possible
        self.reset_dev()

    def reset_dev(self):
        """Reset device paths to allow unmounting."""
        if not self.device:
            return

        self.linked = self.mapped = self.mounted = True

        device = self.device
        if os.path.isabs(device) and os.path.exists(device):
            if device.startswith('/dev/mapper/'):
                device = os.path.basename(device)
                if 'p' in device:
                    device, self.partition = device.rsplit('p', 1)
                    self.device = os.path.join('/dev', device)

    def get_dev(self):
        """Make the image available as a block device in the file system."""
        self.device = None
        self.linked = True
        return True

    def _get_dev_retry_helper(self):
        """Some implementations need to retry their get_dev."""
        # NOTE(mikal): This method helps implement retries. The implementation
        # simply calls _get_dev_retry_helper from their get_dev, and implements
        # _inner_get_dev with their device acquisition logic. The NBD
        # implementation has an example.
        start_time = time.time()
        device = self._inner_get_dev()
        while not device:
            LOG.info('Device allocation failed. Will retry in 2 seconds.')
            time.sleep(2)
            if time.time() - start_time > MAX_DEVICE_WAIT:
                LOG.warning('Device allocation failed after repeated retries.')
                return False
            device = self._inner_get_dev()
        return True

    def _inner_get_dev(self):
        raise NotImplementedError()

    def unget_dev(self):
        """Release the block device from the file system namespace."""
        self.linked = False

    def map_dev(self):
        """Map partitions of the device to the file system namespace."""
        assert(os.path.exists(self.device))
        LOG.debug("Map dev %s", self.device)
        automapped_path = '/dev/%sp%s' % (os.path.basename(self.device),
                                              self.partition)

        if self.partition == -1:
            self.error = _('partition search unsupported with %s') % self.mode
        elif self.partition and not os.path.exists(automapped_path):
            map_path = '/dev/mapper/%sp%s' % (os.path.basename(self.device),
                                              self.partition)
            assert(not os.path.exists(map_path))

            # Note kpartx can output warnings to stderr and succeed
            # Also it can output failures to stderr and "succeed"
            # So we just go on the existence of the mapped device
            _out, err = nova.privsep.fs.create_device_maps(self.device)

            @loopingcall.RetryDecorator(
                    max_retry_count=MAX_FILE_CHECKS - 1,
                    max_sleep_time=FILE_CHECK_INTERVAL,
                    exceptions=IOError)
            def recheck_path(map_path):
                if not os.path.exists(map_path):
                    raise IOError()

            # Note kpartx does nothing when presented with a raw image,
            # so given we only use it when we expect a partitioned image, fail
            try:
                recheck_path(map_path)
                self.mapped_device = map_path
                self.mapped = True
            except IOError:
                if not err:
                    err = _('partition %s not found') % self.partition
                self.error = _('Failed to map partitions: %s') % err
        elif self.partition and os.path.exists(automapped_path):
            # Note auto mapping can be enabled with the 'max_part' option
            # to the nbd or loop kernel modules. Beware of possible races
            # in the partition scanning for _loop_ devices though
            # (details in bug 1024586), which are currently uncatered for.
            self.mapped_device = automapped_path
            self.mapped = True
            self.automapped = True
        else:
            self.mapped_device = self.device
            self.mapped = True

        return self.mapped

    def unmap_dev(self):
        """Remove partitions of the device from the file system namespace."""
        if not self.mapped:
            return
        LOG.debug("Unmap dev %s", self.device)
        if self.partition and not self.automapped:
            nova.privsep.fs.remove_device_maps(self.device)
        self.mapped = False
        self.automapped = False

    def mnt_dev(self):
        """Mount the device into the file system."""
        LOG.debug("Mount %(dev)s on %(dir)s",
                  {'dev': self.mapped_device, 'dir': self.mount_dir})
        out, err = nova.privsep.fs.mount(None, self.mapped_device,
                                         self.mount_dir)
        if err:
            self.error = _('Failed to mount filesystem: %s') % err
            LOG.debug(self.error)
            return False

        self.mounted = True
        return True

    def unmnt_dev(self):
        """Unmount the device from the file system."""
        if not self.mounted:
            return
        self.flush_dev()
        LOG.debug("Umount %s", self.mapped_device)
        nova.privsep.fs.umount(self.mapped_device)
        self.mounted = False

    def flush_dev(self):
        pass

    def do_mount(self):
        """Call the get, map and mnt operations."""
        status = False
        try:
            status = self.get_dev() and self.map_dev() and self.mnt_dev()
        finally:
            if not status:
                LOG.debug("Fail to mount, tearing back down")
                self.do_teardown()
        return status

    def do_umount(self):
        """Call the unmnt operation."""
        if self.mounted:
            self.unmnt_dev()

    def do_teardown(self):
        """Call the umnt, unmap, and unget operations."""
        if self.mounted:
            self.unmnt_dev()
        if self.mapped:
            self.unmap_dev()
        if self.linked:
            self.unget_dev()