b66ff2c298
There are many existing qcow2 images that specify a backing file but no format. This has been the source of CVEs in the past, but has become more prominent of a problem now that libvirt has switched to -blockdev. With older -drive, at least the probing was always done by qemu (so the only risk of a changed format between successive boots of a guest was if qemu was upgraded and probed differently). But with newer -blockdev, libvirt must specify a format; if libvirt guesses raw where the image was formatted, this results in data corruption visible to the guest; conversely, if libvirt guesses qcow2 where qemu was using raw, this can result in potential security holes, so modern libvirt instead refuses to use images without explicit backing format. The change in libvirt to reject images without explicit backing format has pointed out that a number of tools have been far too reliant on probing in the past. It's time to set a better example in our own iotests of properly setting this parameter. iotest calls to create, rebase, and convert are all impacted to some degree. It's a bit annoying that we are inconsistent on command line - while all of those accept -o backing_file=...,backing_fmt=..., the shortcuts are different: create and rebase have -b and -F, while convert has -B but no -F. (amend has no shortcuts, but the previous patch just deprecated the use of amend to change backing chains). Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20200706203954.341758-9-eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
243 lines
7.8 KiB
Python
Executable file
243 lines
7.8 KiB
Python
Executable file
#!/usr/bin/env python3
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#
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# Test for when a backing file is considered overridden (thus, a
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# json:{} filename is generated for the overlay) and when it is not
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#
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# Copyright (C) 2018 Red Hat, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# Creator/Owner: Max Reitz <mreitz@redhat.com>
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import iotests
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from iotests import log, qemu_img, filter_testfiles, filter_imgfmt, \
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filter_qmp_testfiles, filter_qmp_imgfmt
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# Need backing file and change-backing-file support
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iotests.script_initialize(
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supported_fmts=['qcow2', 'qed'],
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supported_platforms=['linux'],
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)
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def log_node_info(node):
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log('')
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log('bs->filename: ' + node['image']['filename'],
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filters=[filter_testfiles, filter_imgfmt])
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log('bs->backing_file: ' + node['backing_file'],
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filters=[filter_testfiles, filter_imgfmt])
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if 'backing-image' in node['image']:
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log('bs->backing->bs->filename: ' +
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node['image']['backing-image']['filename'],
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filters=[filter_testfiles, filter_imgfmt])
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else:
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log('bs->backing: (none)')
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log('')
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with iotests.FilePath('base.img') as base_img_path, \
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iotests.FilePath('top.img') as top_img_path, \
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iotests.VM() as vm:
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assert qemu_img('create', '-f', iotests.imgfmt, base_img_path, '64M') == 0
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# Choose a funny way to describe the backing filename
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assert qemu_img('create', '-f', iotests.imgfmt, '-b',
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'file:' + base_img_path, '-F', iotests.imgfmt,
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top_img_path) == 0
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vm.launch()
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log('--- Implicit backing file ---')
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log('')
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vm.qmp_log('blockdev-add',
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node_name='node0',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': top_img_path
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},
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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# Filename should be plain, and the backing filename should not
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# contain the "file:" prefix
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log_node_info(vm.node_info('node0'))
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vm.qmp_log('blockdev-del', node_name='node0')
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log('')
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log('--- change-backing-file ---')
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log('')
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vm.qmp_log('blockdev-add',
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node_name='node0',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': top_img_path
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},
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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# Changing the backing file to a qemu-reported filename should
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# result in qemu accepting the corresponding BDS as the implicit
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# backing BDS (and thus not generate a json:{} filename).
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# So, first, query the backing filename.
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backing_filename = \
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vm.node_info('node0')['image']['backing-image']['filename']
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# Next, change the backing file to something different
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vm.qmp_log('change-backing-file',
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image_node_name='node0',
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device='node0',
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backing_file='null-co://',
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filters=[filter_qmp_testfiles])
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# Now, verify that we get a json:{} filename
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# (Image header says "null-co://", actual backing file still is
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# base_img_path)
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log_node_info(vm.node_info('node0'))
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# Change it back
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# (To get header and backing file in sync)
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vm.qmp_log('change-backing-file',
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image_node_name='node0',
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device='node0',
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backing_file=backing_filename,
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filters=[filter_qmp_testfiles])
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# And verify that we get our original results
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log_node_info(vm.node_info('node0'))
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# Finally, try a "file:" prefix. While this is actually what we
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# originally had in the image header, qemu will not reopen the
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# backing file here, so it cannot verify that this filename
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# "resolves" to the actual backing BDS's filename and will thus
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# consider both to be different.
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# (This may be fixed in the future.)
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vm.qmp_log('change-backing-file',
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image_node_name='node0',
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device='node0',
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backing_file=('file:' + backing_filename),
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filters=[filter_qmp_testfiles])
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# So now we should get a json:{} filename
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log_node_info(vm.node_info('node0'))
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# Remove and re-attach so we can see that (as in our first try),
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# opening the image anew helps qemu resolve the header backing
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# filename.
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vm.qmp_log('blockdev-del', node_name='node0')
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vm.qmp_log('blockdev-add',
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node_name='node0',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': top_img_path
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},
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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log_node_info(vm.node_info('node0'))
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vm.qmp_log('blockdev-del', node_name='node0')
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log('')
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log('--- Override backing file ---')
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log('')
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# For this test, we need the plain filename in the image header
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# (because qemu cannot "canonicalize"/"resolve" the backing
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# filename unless the backing file is opened implicitly with the
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# overlay)
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assert qemu_img('create', '-f', iotests.imgfmt, '-b', base_img_path,
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'-F', iotests.imgfmt, top_img_path) == 0
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# You can only reliably override backing options by using a node
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# reference (or by specifying file.filename, but, well...)
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vm.qmp_log('blockdev-add', node_name='null', driver='null-co')
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vm.qmp_log('blockdev-add',
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node_name='node0',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': top_img_path
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},
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backing='null',
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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# Should get a json:{} filename (and bs->backing_file is
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# null-co://, because that field actually has not much to do
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# with the header backing filename (except that it is changed by
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# change-backing-file))
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log_node_info(vm.node_info('node0'))
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# Detach the backing file by reopening the whole thing
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vm.qmp_log('blockdev-del', node_name='node0')
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vm.qmp_log('blockdev-del', node_name='null')
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vm.qmp_log('blockdev-add',
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node_name='node0',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': top_img_path
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},
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backing=None,
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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# Should get a json:{} filename (because we overrode the backing
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# file to not be there)
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log_node_info(vm.node_info('node0'))
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# Open the original backing file
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vm.qmp_log('blockdev-add',
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node_name='original-backing',
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driver=iotests.imgfmt,
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file={
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'driver': 'file',
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'filename': base_img_path
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},
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filters=[filter_qmp_testfiles, filter_qmp_imgfmt])
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# Attach the original backing file to its overlay
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vm.qmp_log('blockdev-snapshot',
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node='original-backing',
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overlay='node0')
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# This should give us the original plain result
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log_node_info(vm.node_info('node0'))
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vm.qmp_log('blockdev-del', node_name='node0')
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vm.qmp_log('blockdev-del', node_name='original-backing')
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vm.shutdown()
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