fix(instances): snapshot tab reads less and fails less

The snapshot tab listed the VM's snapshots three times per page: once
per kind and once more for all of them. The list of all is now made
from the two kinds, so the combined flag is no longer used anywhere.

The revert confirm named only the disks the persistent definition
would lose. A disk hot-plugged into the running VM alone is detached
too, so the live definition is compared with what ran when the
snapshot was taken.

A storage pool refresh error after libvirt had already made, reverted
or deleted the snapshot was shown as if the operation had failed. It
is now logged, and the left-behind check is skipped then, since a stale
pool still lists the removed files. A volume removed while that check
reads it is skipped too.

An error reading the block jobs no longer breaks the instance page;
create, revert and delete still query the jobs again and refuse.

vrtManager/tests/test_external_snapshots.py

@@ -98,13 +98,38 @@ class SnapshotListTestCase(unittest.TestCase):
         [entry] = p.get_snapshot(EXTERNAL)
         self.assertEqual(entry["detaches"], [{"dev": "vdb", "path": "/pool/later.qcow2"}])
 
-    def test_detaches_comes_from_the_persistent_definition(self):
+    def test_detaches_covers_the_persistent_and_the_live_definition(self):
         # vdc was hot-plugged into the running VM only; vdb waits for the next start
         live = DOMAIN.replace("/pool/later.qcow2", "/pool/live-only.qcow2").replace("dev='vdb'", "dev='vdc'")
         p = proxy(external=[fake_snap("one")])
         p._XMLDesc = lambda flags: DOMAIN if flags == PERSISTENT_XML else live
         [entry] = p.get_snapshot(EXTERNAL)
-        self.assertEqual(entry["detaches"], [{"dev": "vdb", "path": "/pool/later.qcow2"}])
+        self.assertEqual(
+            entry["detaches"],
+            [{"dev": "vdb", "path": "/pool/later.qcow2"}, {"dev": "vdc", "path": "/pool/live-only.qcow2"}],
+        )
+
+    def test_the_live_definition_is_compared_with_the_snapshots_live_one(self):
+        # taken while vdc was hot-plugged: <domain> is what ran, <inactiveDomain> what was defined
+        snap = fake_snap("one")
+        snap.getXMLDesc.return_value = snapshot_xml("one", disks=("vda", "vdc")).replace(
+            "</domainsnapshot>",
+            "<inactiveDomain><devices><disk type='file' device='disk'><source file='/pool/vda.qcow2'/>"
+            "<target dev='vda'/></disk></devices></inactiveDomain></domainsnapshot>",
+        )
+        persistent = DOMAIN.replace("<disk type='file' device='disk'><source file='/pool/later.qcow2'/><target dev='vdb' bus='virtio'/></disk>", "")
+        live = DOMAIN.replace("/pool/later.qcow2", "/pool/live-only.qcow2").replace("dev='vdb'", "dev='vdc'")
+        p = proxy(external=[snap])
+        p._XMLDesc = lambda flags: persistent if flags == PERSISTENT_XML else live
+        [entry] = p.get_snapshot(EXTERNAL)
+        self.assertEqual(entry["detaches"], [])
+
+    def test_a_shut_off_vm_is_compared_with_the_persistent_definition_only(self):
+        p = proxy(status=5, external=[fake_snap("one", disks=("vda", "vdb"))])
+        p._XMLDesc = MagicMock(return_value=DOMAIN)
+        [entry] = p.get_snapshot(EXTERNAL)
+        self.assertEqual(entry["detaches"], [])
+        p._XMLDesc.assert_called_once_with(PERSISTENT_XML)
 
     def test_lists_are_by_kind(self):
         p = proxy(internal=[fake_snap("i")], external=[fake_snap("e")])
@@ -429,6 +454,8 @@ class LeftBehindTestCase(unittest.TestCase):
         def volume(path):
             if path not in backing:
                 raise libvirtError("no volume")
+            if isinstance(backing[path], Exception):  # removed between the lookup and the read
+                return MagicMock(**{"XMLDesc.side_effect": backing[path]})
             parent = f"<backingStore><path>{backing[path]}</path></backingStore>" if backing[path] else ""
             return MagicMock(**{"XMLDesc.return_value": f"<volume><target><path>{path}</path></target>{parent}</volume>"})
 
@@ -470,6 +497,33 @@ class LeftBehindTestCase(unittest.TestCase):
         left = self.revert(before, CHAIN, {"/pool/linked.qcow2": "/pool/a.one"})
         self.assertEqual(left, [])
 
+    def test_a_volume_gone_while_checking_is_not_reported(self):
+        before = CHAIN.replace("/pool/a.two", "/pool/a.after")
+        after = CHAIN.replace("/pool/a.two", "/pool/a.1700000001")
+        left = self.revert(before, after, {"/pool/a.after": libvirtError("no volume")})
+        self.assertEqual(left, [])
+
+
+class PoolRefreshTestCase(unittest.TestCase):
+    """The pools are refreshed after libvirt made, reverted or deleted the
+    snapshot; a refresh error does not turn that into a failure."""
+
+    def test_create_succeeds_when_the_refresh_fails(self):
+        p = proxy()
+        p.refresh_instance_pools.side_effect = libvirtError("pool busy")
+        p.create_external_snapshot("one")
+        p._snapshotCreateXML.assert_called_once()
+
+    def test_delete_and_revert_succeed_and_report_nothing_when_the_refresh_fails(self):
+        for action in ("delete_external_snapshot", "revert_external_snapshot"):
+            with self.subTest(action):
+                snap = fake_snap("one", current=True)
+                p = proxy(external=[snap])
+                p.refresh_instance_pools.side_effect = libvirtError("pool busy")
+                # a stale pool still lists every file
+                p.get_volume_by_path = MagicMock()
+                self.assertEqual(getattr(p, action)("one"), [])
+
 class KindTestCase(unittest.TestCase):
     def test_internal_endpoints_refuse_external_names(self):
         snap = fake_snap("e")