On 21.01.20 11:40, Vladimir Sementsov-Ogievskiy wrote: > 21.01.2020 12:41, Max Reitz wrote: >> On 21.01.20 10:23, Vladimir Sementsov-Ogievskiy wrote: >>> 21.01.2020 12:14, Max Reitz wrote: >>>> On 20.01.20 18:20, Vladimir Sementsov-Ogievskiy wrote: >>>>> 20.01.2020 20:04, Max Reitz wrote: >>>>>> On 16.01.20 16:54, Vladimir Sementsov-Ogievskiy wrote: >>>>>>> This test checks that bug is really fixed by previous commit. >>>>>>> >>>>>>> Cc: qemu-sta...@nongnu.org # v4.2.0 >>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> >>>>>>> --- >>>>>>> tests/qemu-iotests/283 | 75 >>>>>>> ++++++++++++++++++++++++++++++++++++++ >>>>>>> tests/qemu-iotests/283.out | 8 ++++ >>>>>>> tests/qemu-iotests/group | 1 + >>>>>>> 3 files changed, 84 insertions(+) >>>>>>> create mode 100644 tests/qemu-iotests/283 >>>>>>> create mode 100644 tests/qemu-iotests/283.out >>>>>> >>>>>> The test looks good to me, I just have a comment nit and a note on the >>>>>> fact that this should probably be queued only after Thomas’s “Enable >>>>>> more iotests during "make check-block"” series. >>>>>> >>>>>>> diff --git a/tests/qemu-iotests/283 b/tests/qemu-iotests/283 >>>>>>> new file mode 100644 >>>>>>> index 0000000000..f0f216d109 >>>>>>> --- /dev/null >>>>>>> +++ b/tests/qemu-iotests/283 >>>>>>> @@ -0,0 +1,75 @@ >>>>>>> +#!/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 >>>>>>> + >>>>>>> +""" >>>>>>> +On activation, backup-top is going to unshare write permission on its >>>>>>> +source child. It will be impossible for the following configuration: >>>>>> >>>>>> “The following configuration will become impossible”? >>>>> >>>>> Hmm, no, the configuration is possible. But "it", i.e. "unshare write >>>>> permission", >>>>> is impossible with such configuration.. >>>> >>>> But backup_top always unshares the write permission on the source. >>> >>> Yes, and I just try to say, that this action will fail. And the test checks >>> that it >>> fails (and it crashes with current master instead of fail). >> >> OK. So what I was trying to say is that the comment currently only >> states that this will fail. I’d prefer it to also reassure me that it’s >> correct that this fails (because all writes on the backup source must go >> through backup_top), and that this is exactly what we want to test here. >> >> On first reading, I was wondering why exactly this comment would tell me >> all these things, because I didn’t know what the test wants to test in >> the first place. >> >> Max > > Hmm, something like: > > Backup wants to copy a point-in-time state of the source node. So, it catches > all writes > to the source node by appending backup-top filter above it. So we handle all > changes which > comes from source node parents. To prevent appearing of new writing parents > during the > progress, backup-top unshares write permission on its source child. This has > additional > implication: as this "unsharing" is propagated by default by backing/file > children, > backup-top conflicts with any side parents of source sub-tree with write > permission. > And this is in good relation with the general idea: with such parents we > can't guarantee > point-in-time backup.
Works for me (thanks :-)), but a shorter “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. Therefore, backup-top cannot allow other nodes to change data on its source child.” would work for me just as well. > So, trying to backup the configuration with writing side parents of > source sub-tree nodes should fail. Let's test it. Max
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