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[PATCH for-5.0 v2 23/23] iotests: Mirror must not attempt to create loop
From: |
Max Reitz |
Subject: |
[PATCH for-5.0 v2 23/23] iotests: Mirror must not attempt to create loops |
Date: |
Mon, 11 Nov 2019 17:02:16 +0100 |
Signed-off-by: Max Reitz <address@hidden>
---
tests/qemu-iotests/041 | 235 +++++++++++++++++++++++++++++++++++++
tests/qemu-iotests/041.out | 4 +-
2 files changed, 237 insertions(+), 2 deletions(-)
diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index 9a00cf6f7b..0e43bb699d 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -1246,6 +1246,241 @@ class TestReplaces(iotests.QMPTestCase):
self.vm.assert_block_path('filter0', '/file', 'target')
+ """
+ See what happens when the @sync/@replaces configuration dictates
+ creating a loop.
+ """
+ @iotests.skip_if_unsupported(['throttle'])
+ def test_loop(self):
+ qemu_img('create', '-f', iotests.imgfmt, test_img, str(1 * 1024 *
1024))
+
+ # Dummy group so we can create a NOP filter
+ result = self.vm.qmp('object-add', qom_type='throttle-group', id='tg0')
+ self.assert_qmp(result, 'return', {})
+
+ result = self.vm.qmp('blockdev-add', **{
+ 'driver': 'throttle',
+ 'node-name': 'source',
+ 'throttle-group': 'tg0',
+ 'file': {
+ 'driver': iotests.imgfmt,
+ 'node-name': 'filtered',
+ 'file': {
+ 'driver': 'file',
+ 'filename': test_img
+ }
+ }
+ })
+ self.assert_qmp(result, 'return', {})
+
+ # Block graph is now:
+ # source[throttle] --file--> filtered[imgfmt] --file--> ...
+
+ result = self.vm.qmp('drive-mirror', job_id='mirror', device='source',
+ target=target_img, format=iotests.imgfmt,
+ node_name='target', sync='none',
+ replaces='filtered')
+
+ """
+ Block graph before mirror exits would be (ignoring mirror_top):
+ source[throttle] --file--> filtered[imgfmt] --file--> ...
+ target[imgfmt] --file--> ...
+
+ Then, because of sync=none and drive-mirror in absolute-paths mode,
+ the source is attached to the target:
+ source[throttle] --file--> filtered[imgfmt] --file--> ...
+ ^
+ backing
+ |
+ target[imgfmt] --file--> ...
+
+ Replacing filtered by target would yield:
+ source[throttle] --file--> target[imgfmt] --file--> ...
+ ^ |
+ +------- backing --------+
+
+ I.e., a loop. bdrv_replace_node() detects this and simply
+ does not let source's file link point to target. However,
+ that means that target cannot really replace source.
+
+ drive-mirror should detect this and not allow this case.
+ """
+
+ self.assert_qmp(result, 'error/desc',
+ "Replacing 'filtered' by 'target' with this sync " + \
+ "mode would result in a loop, because the former " + \
+ "would be a child of the latter's backing file " + \
+ "('source') after the mirror job")
+
+ """
+ Test what happens when there would be no loop with the pre-mirror
+ configuration, but something changes during the mirror job that asks
+ for a loop to be created during completion.
+ """
+ @iotests.skip_if_unsupported(['copy-on-read', 'quorum'])
+ def test_loop_during_mirror(self):
+ qemu_img('create', '-f', iotests.imgfmt, test_img, str(1 * 1024 *
1024))
+
+ """
+ In this test, we are going to mirror from a node that is a
+ filter above some file "common-base". The target is a quorum
+ node (with just an unrelated null-co child).
+
+ We will ask the mirror job to replace common-base by the
+ target upon completion. That is a completely valid
+ configuration so far.
+
+ However, while the job is running, we add common-base as an
+ (indirect[1]) child to the target quorum node. This way,
+ completing the job as requested would yield a loop, because
+ the target would be supposed to replace common-base -- which
+ is its own (indirect) child.
+
+ [1] It needs to be an indirect child, because if it were a
+ direct child, the mirror job would simply end by effectively
+ injecting the target above common-base. This is the same
+ effect as when using sync=none: The target ends up above the
+ source.
+
+ So only loops that have a length of more than one node are
+ forbidden, which means common-base must be an indirect child
+ of the target.
+
+ (Furthermore, we are going to use x-blockdev-change to add
+ common-base as a child to the target. This command only
+ allows doing so for nodes that have no parent yet.
+ common-base will have a parent already, though, namely the
+ source node. Therefore, this is another reason why we need at
+ least one node above common-base, so this parent can become
+ target's child during the mirror.)
+ """
+
+ result = self.vm.qmp('blockdev-add', **{
+ 'driver': 'null-co',
+ 'node-name': 'common-base',
+ 'read-zeroes': True,
+ 'size': 1 * 1024 * 1024
+ })
+ self.assert_qmp(result, 'return', {})
+
+ result = self.vm.qmp('blockdev-add', **{
+ 'driver': 'copy-on-read',
+ 'node-name': 'source',
+ 'file': 'common-base'
+ })
+ self.assert_qmp(result, 'return', {})
+
+ """
+ As explained above, we have to create a parent above
+ common-base.
+
+ We cannot use any parent that would forward the RESIZE
+ permission, because the job takes it on the target, but
+ unshares it on the source: After the x-blockdev-change
+ operation during the mirror job, this parent will be a child
+ of the target, so common-base will be an (indirect) child of
+ both the mirror's source and target. Thus, the job would
+ conflict with itself.
+
+ Therefore, we make common-base a backing child of a $imgfmt
+ node. Unfortunately, we cannot let the mirror job replace a
+ node that acts as a backing child somewhere (because of an op
+ blocker), so we put another raw node between the $imgfmt node
+ and common-base.
+ """
+ result = self.vm.qmp('blockdev-add', **{
+ 'driver': iotests.imgfmt,
+ 'node-name': 'base-parent',
+ 'file': {
+ 'driver': 'file',
+ 'filename': test_img
+ },
+ 'backing': {
+ 'driver': 'raw',
+ 'file': 'common-base'
+ }
+ })
+
+ """
+ Add a quorum node with a single child, we will add base-parent
+ to prepare a loop later.
+ (We do not care about this single child at all, but it is
+ impossible to create a quorum node without any children. We
+ will ignore this child from now on.)
+ """
+ result = self.vm.qmp('blockdev-add', **{
+ 'driver': 'quorum',
+ 'node-name': 'target',
+ 'vote-threshold': 1,
+ 'children': [
+ {
+ 'driver': 'null-co',
+ 'read-zeroes': True,
+ 'size': 1 * 1024 * 1024
+ }
+ ]
+ })
+ self.assert_qmp(result, 'return', {})
+
+ """
+ Current block graph:
+
+ base-parent[$imgfmt] --backing--> [raw]
+ |
+ file
+ v
+ source[COR] --file--> common-base[null-co]
+
+ target[quorum]
+
+
+ The following blockdev-mirror asks for this graph post-mirror:
+
+ base-parent[$imgfmt] --backing--> [raw]
+ |
+ file
+ v
+ source[COR] --file--> target[quorum]
+
+ That would be a valid configuration without any loops.
+ """
+
+ result = self.vm.qmp('blockdev-mirror', job_id='mirror',
+ device='source', target='target', sync='full',
+ replaces='common-base')
+ self.assert_qmp(result, 'return', {})
+
+ """
+ However, now we will make base-parent a child of target.
+ Before the mirror job completes, that is still completely
+ valid:
+
+ source
+ |
+ v
+ target -> base-parent -> [raw] -> common-base
+ """
+
+ result = self.vm.qmp('x-blockdev-change',
+ parent='target', node='base-parent')
+ self.assert_qmp(result, 'return', {})
+
+ """
+ However, post-mirror, we thus ask for a loop:
+
+ source -> target (replaced common-base) -> base-parent
+ ^ |
+ | v
+ +----------------- [raw]
+
+ bdrv_replace_node() would not allow such a configuration, but
+ we should not pretend we can create it, so the mirror job
+ should fail during completion.
+ """
+
+ self.complete_and_wait('mirror',
+ completion_error='Operation not permitted')
+
if __name__ == '__main__':
iotests.main(supported_fmts=['qcow2', 'qed'],
supported_protocols=['file'])
diff --git a/tests/qemu-iotests/041.out b/tests/qemu-iotests/041.out
index 877b76fd31..20a8158b99 100644
--- a/tests/qemu-iotests/041.out
+++ b/tests/qemu-iotests/041.out
@@ -1,5 +1,5 @@
-..............................................................................................
+................................................................................................
----------------------------------------------------------------------
-Ran 94 tests
+Ran 96 tests
OK
--
2.23.0
- Re: [PATCH for-5.0 v2 15/23] mirror: Prevent loops, (continued)
[PATCH for-5.0 v2 19/23] iotests: Resolve TODOs in 041, Max Reitz, 2019/11/11
[PATCH for-5.0 v2 17/23] iotests: Use skip_if_unsupported decorator in 041, Max Reitz, 2019/11/11
[PATCH for-5.0 v2 18/23] iotests: Add VM.assert_block_path(), Max Reitz, 2019/11/11
[PATCH for-5.0 v2 20/23] iotests: Use self.image_len in TestRepairQuorum, Max Reitz, 2019/11/11
[PATCH for-5.0 v2 22/23] iotests: Check that @replaces can replace filters, Max Reitz, 2019/11/11
[PATCH for-5.0 v2 21/23] iotests: Add tests for invalid Quorum @replaces, Max Reitz, 2019/11/11
[PATCH for-5.0 v2 23/23] iotests: Mirror must not attempt to create loops,
Max Reitz <=
Re: [PATCH for-5.0 v2 00/23] block: Fix check_to_replace_node(), Vladimir Sementsov-Ogievskiy, 2019/11/29