bootstrap-vz/bootstrapvz/common/fs/qemuvolume.py

from .loopbackvolume import LoopbackVolume
from bootstrapvz.base.fs.exceptions import VolumeError
from ..tools import log_check_call
from . import get_partitions


class QEMUVolume(LoopbackVolume):

    def _before_create(self, e):
        self.image_path = e.image_path
        vol_size = str(self.size.bytes.get_qty_in('MiB')) + 'M'
        log_check_call(['qemu-img', 'create', '-f', self.qemu_format, self.image_path, vol_size])

    def _check_nbd_module(self):
        from bootstrapvz.base.fs.partitionmaps.none import NoPartitions
        if isinstance(self.partition_map, NoPartitions):
            if not self._module_loaded('nbd'):
                msg = ('The kernel module `nbd\' must be loaded '
                       '(`modprobe nbd\') to attach .{extension} images'
                       .format(extension=self.extension))
                raise VolumeError(msg)
        else:
            num_partitions = len(self.partition_map.partitions)
            if not self._module_loaded('nbd'):
                msg = ('The kernel module `nbd\' must be loaded '
                       '(run `modprobe nbd max_part={num_partitions}\') '
                       'to attach .{extension} images'
                       .format(num_partitions=num_partitions, extension=self.extension))
                raise VolumeError(msg)
            nbd_max_part = int(self._module_param('nbd', 'max_part'))
            if nbd_max_part < num_partitions:
                # Found here: http://bethesignal.org/blog/2011/01/05/how-to-mount-virtualbox-vdi-image/
                msg = ('The kernel module `nbd\' was loaded with the max_part '
                       'parameter set to {max_part}, which is below '
                       'the amount of partitions for this volume ({num_partitions}). '
                       'Reload the nbd kernel module with max_part set to at least {num_partitions} '
                       '(`rmmod nbd; modprobe nbd max_part={num_partitions}\').'
                       .format(max_part=nbd_max_part, num_partitions=num_partitions))
                raise VolumeError(msg)

    def _before_attach(self, e):
        self._check_nbd_module()
        self.loop_device_path = self._find_free_nbd_device()
        log_check_call(['qemu-nbd', '--connect', self.loop_device_path, self.image_path])
        self.device_path = self.loop_device_path

    def _before_detach(self, e):
        log_check_call(['qemu-nbd', '--disconnect', self.loop_device_path])
        del self.loop_device_path
        self.device_path = None

    def _module_loaded(self, module):
        import re
        regexp = re.compile('^{module} +'.format(module=module))
        with open('/proc/modules') as loaded_modules:
            for line in loaded_modules:
                match = regexp.match(line)
                if match is not None:
                    return True
        return False

    def _module_param(self, module, param):
        import os.path
        param_path = os.path.join('/sys/module', module, 'parameters', param)
        with open(param_path) as param_file:
            return param_file.read().strip()

    # From http://lists.gnu.org/archive/html/qemu-devel/2011-11/msg02201.html
    # Apparently it's not in the current qemu-nbd shipped with wheezy
    def _is_nbd_used(self, device_name):
        return device_name in get_partitions()

    def _find_free_nbd_device(self):
        import os.path
        for i in xrange(0, 15):
            device_name = 'nbd' + str(i)
            if not self._is_nbd_used(device_name):
                return os.path.join('/dev', device_name)
        raise VolumeError('Unable to find free nbd device.')

    def __setstate__(self, state):
        for key in state:
            self.__dict__[key] = state[key]