iotests: add test for backup-top failure on permission activation

#!/usr/bin/env python

#

# Test for backup-top filter permission activation failure

#

# Copyright (c) 2019 Virtuozzo International GmbH.

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program.  If not, see <http://www.gnu.org/licenses/>.

#

import iotests

# The test is unrelated to formats, restrict it to qcow2 to avoid extra runs

iotests.verify_image_format(supported_fmts=['qcow2'])

size = 1024 * 1024

""" Test description

When performing a backup, all writes on the source subtree must go through the

backup-top filter so it can copy all data to the target before it is changed.

backup-top filter is appended above source node, to achieve this thing, so all

parents of source node are handled. A configuration with side parents of source

sub-tree with write permission is unsupported (we'd have append several

backup-top filter like nodes to handle such parents). The test create an

example of such configuration and checks that a backup is then not allowed

(blockdev-backup command should fail).

The configuration:

    ┌────────┐  target  ┌─────────────┐

    │ target │ ◀─────── │ backup_top  │

    └────────┘          └─────────────┘

                            │

                            │ backing

                            ▼

                        ┌─────────────┐

                        │   source    │

                        └─────────────┘

                            │

                            │ file

                            ▼

                        ┌─────────────┐  write perm   ┌───────┐

                        │    base     │ ◀──────────── │ other │

                        └─────────────┘               └───────┘

On activation (see .active field of backup-top state in block/backup-top.c),

backup-top is going to unshare write permission on its source child. Write

unsharing will be propagated to the "source->base" link and will conflict with

other node write permission. So permission update will fail and backup job will

not be started.

Note, that the only thing which prevents backup of running on such

configuration is default permission propagation scheme. It may be altered by

different block drivers, so backup will run in invalid configuration. But

something is better than nothing. Also, before the previous commit (commit

preceding this test creation), starting backup on such configuration led to

crash, so current "something" is a lot better, and this test actual goal is

to check that crash is fixed :)

"""

vm = iotests.VM()

vm.launch()

vm.qmp_log('blockdev-add', **{'node-name': 'target', 'driver': 'null-co'})

vm.qmp_log('blockdev-add', **{

    'node-name': 'source',

    'driver': 'blkdebug',

    'image': {'node-name': 'base', 'driver': 'null-co', 'size': size}

})

vm.qmp_log('blockdev-add', **{

    'node-name': 'other',

    'driver': 'blkdebug',

    'image': 'base',

    'take-child-perms': ['write']

})

vm.qmp_log('blockdev-backup', sync='full', device='source', target='target')

vm.shutdown()

{"execute": "blockdev-add", "arguments": {"driver": "null-co", "node-name": "target"}}

{"return": {}}

{"execute": "blockdev-add", "arguments": {"driver": "blkdebug", "image": {"driver": "null-co", "node-name": "base", "size": 1048576}, "node-name": "source"}}

{"return": {}}

{"execute": "blockdev-add", "arguments": {"driver": "blkdebug", "image": "base", "node-name": "other", "take-child-perms": ["write"]}}

{"return": {}}

{"execute": "blockdev-backup", "arguments": {"device": "source", "sync": "full", "target": "target"}}

{"error": {"class": "GenericError", "desc": "Cannot set permissions for backup-top filter: Conflicts with use by other as 'image', which uses 'write' on base"}}

279 rw backing quick

280 rw migration quick

281 rw quick

283 auto quick