72 lines
2.8 KiB
Python
72 lines
2.8 KiB
Python
# 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)
|