CA-260245: Fix SXM: old host choking on new op

Storage migration was failing when the source was an older
XenServer host with no knowledge of the `cbt_enable and
`cbt_disable VDI operations.

This commit filters out these operations when
populating a VDI's allowed_operations list.

Signed-off-by: Thomas Sanders <[email protected]>

Author: thomassa

ocaml/xapi/test_vdi_allowed_operations.ml

@@ -302,8 +302,10 @@ let test_operations_restricted_during_rpu =
     Xapi_vdi.update_allowed_operations ~__context ~self;
     OUnit.assert_bool "update_allowed_operations should exclude `enable_cbt during RPU" (not @@ List.mem `enable_cbt (Db.VDI.get_allowed_operations ~__context ~self));
     Db.Pool.remove_from_other_config ~__context ~self:pool ~key:Xapi_globs.rolling_upgrade_in_progress;
-    Xapi_vdi.update_allowed_operations ~__context ~self;
+    Xapi_vdi.update_allowed_operations ~__context ~self
+    (* CA-260245: at present update_allowed_operations excludes the cbt operations unconditionally.
     OUnit.assert_bool "update_allowed_operations should consider `enable_cbt when RPU is not running" (List.mem `enable_cbt (Db.VDI.get_allowed_operations ~__context ~self))
+    *)
   in
 
   "test_operations_restricted_during_rpu" >:::

ocaml/xapi/xapi_vdi.ml

@@ -253,11 +253,17 @@ let update_allowed_operations_internal ~__context ~self ~sr_records ~pbd_records
   let pool = Helpers.get_pool ~__context in
   let ha_enabled = Db.Pool.get_ha_enabled ~__context ~self:pool in
 
+  let all_ops = Listext.List.set_difference
+    (* Older XenServers choke on ops they don't recognise during SXM, so
+     * filter out the recently added ones: CA-260245 *)
+    Xapi_vdi_helpers.all_ops
+    (`blocked :: Xapi_vdi_helpers.recently_added_ops)
+  in
   let all = Db.VDI.get_record_internal ~__context ~self in
   let allowed =
     let check x = match check_operation_error ~__context ~sr_records ~pbd_records ~vbd_records ha_enabled all self x with None ->  [ x ] | _ -> [] in
-    List.fold_left (fun accu op -> check op @ accu) []
-      (Listext.List.set_difference Xapi_vdi_helpers.all_ops [`blocked]) in
+    List.fold_left (fun accu op -> check op @ accu) [] all_ops
+  in
   let allowed =
     if Helpers.rolling_upgrade_in_progress ~__context
     then Listext.List.intersect allowed Xapi_globs.rpu_allowed_vdi_operations

ocaml/xapi/xapi_vdi_helpers.ml

@@ -42,6 +42,24 @@ let all_ops: API.vdi_operations list =
   ; `update
   ]
 
+(* CA-260245: older XenServer versions do not know about these operations,
+ * and therefore cannot do storage migration to a XenServer that lists them
+ * in a VDI's allowed_operations field.
+ * As a temporary measure, we are fixing the symptom by excluding these ops
+ * from the allowed_operations list. This is a hack: TECHNICAL DEBT.
+ * If we were to continue with this mechanism then any additional new ops would
+ * have to be added to this recently_added_ops list, and we would be able to
+ * remove items when old-but-supported XenServer versions know about them.
+ * We would prefer to do a more general fix for this class of problems; we have
+ * one or two approaches in mind. *)
+let recently_added_ops: API.vdi_operations list =
+  (* If/when items are removed from this list, update
+   * test_vdi_allowed_operations.ml to re-enable (and maybe alter)
+   * the relevant part of test_update_allowed_operations. *)
+  [ `enable_cbt
+  ; `disable_cbt
+  ]
+
 (* CA-26514: Block operations on 'unmanaged' VDIs *)
 let assert_managed ~__context ~vdi =
   if not (Db.VDI.get_managed ~__context ~self:vdi)