diskimage-builder/diskimage_builder/block_device/level3/mount.py

# Copyright 2017 Andreas Florath (andreas@florath.net)
#
# 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 functools
import logging
import os
import time

from diskimage_builder.block_device.exception \
    import BlockDeviceSetupException
from diskimage_builder.block_device.plugin import NodeBase
from diskimage_builder.block_device.plugin import PluginBase
from diskimage_builder.block_device.utils import exec_sudo


logger = logging.getLogger(__name__)


class MountPointNode(NodeBase):

    def __init__(self, mount_base, config, state):
        super(MountPointNode, self).__init__(config['name'], state)

        # Parameter check
        self.mount_base = mount_base
        for pname in ['base', 'mount_point']:
            if pname not in config:
                raise BlockDeviceSetupException(
                    "MountPoint config needs [%s]" % pname)
            setattr(self, pname, config[pname])
        logger.debug("MountPoint created [%s]", self)

    def get_edges(self):
        """Insert all edges

        The dependency edge is created in all cases from the base
        element (typically a mkfs) and, if this is not the 'first'
        mount-point, an edge is created from the mount-point before in
        "sorted order" (see :func:`sort_mount_points`).  This ensures
        that during mounting (and umounting) the globally correct
        order is used.
        """
        edge_from = []
        edge_to = []

        # should have been added by __init__...
        assert 'sorted_mount_points' in self.state
        sorted_mount_points = self.state['sorted_mount_points']

        # If we are not first, add our parent in the global dependency
        # list.  sorted_mount_points is tuples (mount_point, node_name).
        # find ourselves in the mount_points, and our parent node
        # is one before us in node_name list.
        mount_points = [x[0] for x in sorted_mount_points]
        node_name = [x[1] for x in sorted_mount_points]
        mpi = mount_points.index(self.mount_point)
        if mpi > 0:
            dep = node_name[mpi - 1]
            edge_from.append(dep)

        edge_from.append(self.base)
        return (edge_from, edge_to)

    def create(self):
        logger.debug("mount called [%s]", self.mount_point)
        rel_mp = self.mount_point if self.mount_point[0] != '/' \
                 else self.mount_point[1:]
        mount_point = os.path.join(self.mount_base, rel_mp)
        if not os.path.exists(mount_point):
            # Need to sudo this because of permissions in the new
            # file system tree.
            exec_sudo(['mkdir', '-p', mount_point])
        logger.info("Mounting [%s] to [%s]", self.name, mount_point)
        exec_sudo(["mount", self.state['filesys'][self.base]['device'],
                   mount_point])

        if 'mount' not in self.state:
            self.state['mount'] = {}
        self.state['mount'][self.mount_point] \
            = {'name': self.name, 'base': self.base, 'path': mount_point}

        if 'mount_order' not in self.state:
            self.state['mount_order'] = []
        self.state['mount_order'].append(self.mount_point)

    def umount(self):
        logger.info("Called for [%s]", self.name)
        # Before calling umount, call 'fstrim' on suitable mounted
        # file systems.  This discards unused blocks from the mounted
        # file system and therefore decreases the resulting image
        # size.
        #
        # A race condition can occur when trying to fstrim immediately
        # after deleting a file resulting in that free space not being
        # reclaimed.  Calling sync before fstrim is a workaround for
        # this behaviour.
        # https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg02978.html
        exec_sudo(["sync"])
        if self.state['filesys'][self.base]['fstype'] != 'vfat':
            exec_sudo(["fstrim", "--verbose",
                       self.state['mount'][self.mount_point]['path']])
        # Even 'fstrim' call sometimes don't solve the issue with 'busy'
        # filesystem, so we need to catch the exception and repeat unount.
        mount_point = self.state['mount'][self.mount_point]['path']
        catch = None
        for try_cnt in range(10, 1, -1):
            try:
                exec_sudo(["umount", mount_point])
                return
            except BlockDeviceSetupException as e:
                catch = e
                logger.error("umount failed (%s)", e.output.strip())
                time.sleep(3)

        logger.debug("Gave up trying to umount [%s]", mount_point)
        raise catch

    def delete(self):
        self.umount()


def cmp_mount_order(this, other):
    """Sort comparision function for mount-point sorting

    See if ``this`` comes before ``other`` in mount-order list.  In
    words: if the other mount-point has us as it's parent, we come
    before it (are less than it). e.g. ``/var < /var/log <
    /var/log/foo``

    :param this: tuple of mount_point, node name
    :param other: tuple of mount_point, node name
    :returns int: cmp value

    """
    # sort is only based on the mount_point.
    this, _ = this
    other, _ = other
    if this == other:
        return 0
    if other.startswith(this):
        return -1
    else:
        return 1


class Mount(PluginBase):
    def __init__(self, config, defaults, state):
        super(Mount, self).__init__()

        if 'mount-base' not in defaults:
            raise BlockDeviceSetupException(
                "Mount default config needs 'mount-base'")
        self.node = MountPointNode(defaults['mount-base'], config, state)

        # save this new node to the global mount-point list and
        # re-order it to keep it in mount-order.  Used in get_edges()
        # to ensure we build the mount graph in order
        #
        # note we can't just put the MountPointNode into the state,
        # because it's not json serialisable and we still dump the
        # state to json.  that's why we have this (mount_point, name)
        # tuples and sorting trickery
        sorted_mount_points = state.get('sorted_mount_points', [])
        mount_points = [mp for mp, name in sorted_mount_points]
        if self.node.mount_point in mount_points:
            raise BlockDeviceSetupException(
                "Mount point [%s] specified more than once"
                % self.node.mount_point)
        sorted_mount_points.append((self.node.mount_point, self.node.name))
        sorted_mount_points.sort(key=functools.cmp_to_key(cmp_mount_order))
        # Save the state if it's new (otherwise this is idempotent update)
        state['sorted_mount_points'] = sorted_mount_points
        logger.debug("Ordered mounts now: %s", sorted_mount_points)

    def get_nodes(self):
        return [self.node]