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# Copyright 2018 Michael Still and Aptira
#
# 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.
"""
Helpers for qemu tasks.
"""
from oslo_concurrency import processutils
from oslo_log import log as logging
import nova.privsep.utils
LOG = logging.getLogger(__name__)
@nova.privsep.sys_admin_pctxt.entrypoint
def convert_image(source, dest, in_format, out_format, instances_path,
compress):
unprivileged_convert_image(source, dest, in_format, out_format,
instances_path, compress)
# NOTE(mikal): this method is deliberately not wrapped in a privsep entrypoint
def unprivileged_convert_image(source, dest, in_format, out_format,
instances_path, compress):
# NOTE(mdbooth, kchamart): `qemu-img convert` defaults to
# 'cache=writeback' for the source image, and 'cache=unsafe' for the
# target, which means that data is not synced to disk at completion.
# We explicitly use 'cache=none' here, for the target image, to (1)
# ensure that we don't interfere with other applications using the
# host's I/O cache, and (2) ensure that the data is on persistent
# storage when the command exits. Without (2), a host crash may
# leave a corrupt image in the image cache, which Nova cannot
# recover automatically.
# NOTE(zigo, kchamart): We cannot use `qemu-img convert -t none` if
# the 'instance_dir' is mounted on a filesystem that doesn't support
# O_DIRECT, which is the case, for example, with 'tmpfs'. This
# simply crashes `openstack server create` in environments like live
# distributions. In such cases, the best choice is 'writeback',
# which (a) makes the conversion multiple times faster; and (b) is
# as safe as it can be, because at the end of the conversion it,
# just like 'writethrough', calls fsync(2)|fdatasync(2), which
# ensures to safely write the data to the physical disk.
if nova.privsep.utils.supports_direct_io(instances_path):
cache_mode = 'none'
else:
cache_mode = 'writeback'
cmd = ('qemu-img', 'convert', '-t', cache_mode, '-O', out_format)
if in_format is not None:
cmd = cmd + ('-f', in_format)
if compress:
cmd += ('-c',)
cmd = cmd + (source, dest)
processutils.execute(*cmd)
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