[PATCH 22/22] iotests: Mirror must not attempt to create loops

[Max Reitz <mreitz@redhat.com>]

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/041     | 152 +++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/041.out |   4 +-
 2 files changed, 154 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index e4cc829fe2..6ea4764ae8 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -1265,6 +1265,158 @@ class TestReplaces(iotests.QMPTestCase):
 
         self.vm.assert_block_path('filter0/file', 'target')
 
+    '''
+    See what happens when the @sync/@replaces configuration dictates
+    creating a loop.
+    '''
+    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[qcow2] --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[qcow2] --file--> ...
+          target[qcow2] --file--> ...
+
+        Then, because of sync=none and drive-mirror in absolute-paths mode,
+        the source is attached to the target:
+          source[throttle] --file--> filtered[qcow2] --file--> ...
+                 ^
+              backing
+                 |
+            target[qcow2] --file--> ...
+
+        Replacing filtered by target would yield:
+          source[throttle] --file--> target[qcow2] --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.
+    '''
+    def test_loop_during_mirror(self):
+        qemu_img('create', '-f', iotests.imgfmt, test_img, str(1 * 1024 * 1024))
+
+        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', {})
+
+        '''
+        x-blockdev-change can only add children to a quorum node that
+        have no parent yet, so we need an intermediate node between
+        target and common-base that has no parents other than target.
+        We cannot use any parent that would forward the RESIZE
+        permission (because the job takes it, but unshares it on the
+        source), so we make it a backing child of a qcow2 node.
+        Unfortunately, we cannot add backing files to Quorum nodes
+        (because of an op blocker), so we put another raw node between
+        the qcow2 node and common-base.
+        '''
+        result = self.vm.qmp('blockdev-add', **{
+                                 'driver': 'qcow2',
+                                 '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
+        result = self.vm.qmp('blockdev-add', **{
+                                 'driver': 'quorum',
+                                 'node-name': 'target',
+                                 'vote-threshold': 1,
+                                 'children': [
+                                     {
+                                         'driver': 'null-co',
+                                         'read-zeroes': True
+                                     }
+                                 ]
+                             })
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('blockdev-mirror', job_id='mirror',
+                             device='source', target='target', sync='full',
+                             replaces='common-base')
+        self.assert_qmp(result, 'return', {})
+
+        result = self.vm.qmp('x-blockdev-change',
+                             parent='target', node='base-parent')
+        self.assert_qmp(result, 'return', {})
+
+        '''
+        This asks for this configuration post-mirror:
+
+        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
-- 
2.21.0