fixup for xapi_vm_helpers.ml

Signed-off-by: Gang Ji <gang.ji@citrix.com>

ocaml/xapi/xapi_vm_helpers.ml

@@ -1036,6 +1036,13 @@ let rank_hosts_by_vm_cnt_in_group ~__context group hosts =
     (fun h -> RefMap.find_opt h host_map |> Option.value ~default:0)
     hosts
 
+let get_affinity_host ~__context ~vm =
+  match Db.VM.get_affinity ~__context ~self:vm with
+  | ref when Db.is_valid_ref __context ref ->
+      Some ref
+  | _ ->
+      None
+
 (* Group all hosts to 2 parts:
    1. A list of affinity host (only one host).
    2. A list of lists, each list contains hosts with the same number of
@@ -1050,36 +1057,40 @@ let rank_hosts_by_vm_cnt_in_group ~__context group hosts =
    ]
 *)
 let rank_hosts_by_placement ~__context ~vm ~group =
-  let affinity_host =
-    match Db.VM.get_affinity ~__context ~self:vm with
-    | ref when Db.is_valid_ref __context ref ->
-        [ref]
-    | _ ->
-        []
-  in
-  let hosts_without_affinity_host =
-    Db.Host.get_all ~__context
-    |> List.filter (fun host -> not (List.mem host affinity_host))
+  let hosts = Db.Host.get_all ~__context in
+  let affinity_host = get_affinity_host ~__context ~vm in
+  let hosts_without_affinity =
+    Option.fold ~none:hosts
+      ~some:(fun host -> List.filter (( <> ) host) hosts)
+      affinity_host
   in
   let sorted_hosts =
-    hosts_without_affinity_host
+    hosts_without_affinity
     |> rank_hosts_by_vm_cnt_in_group ~__context group
-    |> List.map (fun g -> List.map fst g)
+    |> List.(map (map fst))
   in
-  affinity_host :: sorted_hosts |> List.filter (( <> ) [])
+  match affinity_host with
+  | Some host ->
+      [host] :: sorted_hosts
+  | None ->
+      sorted_hosts
 
 let rec select_host_from_ranked_groups vm host_selector groups_of_hosts =
   match groups_of_hosts with
   | [] ->
       raise (Api_errors.Server_error (Api_errors.no_hosts_available, []))
   | hosts :: less_optimal_groups_of_hosts -> (
-      debug "Attempting to start VM (%s) on one of equally optimal hosts [ %s ]"
-        (Ref.string_of vm)
-        (String.concat ";" (List.map Ref.string_of hosts)) ;
+      let hosts_str = String.concat ";" (List.map Ref.string_of hosts) in
+      debug
+        "Attempting to select host for VM (%s) in a group of equally optimal \
+         hosts [ %s ]"
+        (Ref.string_of vm) hosts_str ;
       try host_selector hosts
       with _ ->
-        info "Failed to start VM (%s) on any of [ %s ]" (Ref.string_of vm)
-          (String.concat ";" (List.map Ref.string_of hosts)) ;
+        info
+          "Failed to select host for VM (%s) in any of [ %s ], continue to \
+           select from less optimal hosts"
+          (Ref.string_of vm) hosts_str ;
         select_host_from_ranked_groups vm host_selector
           less_optimal_groups_of_hosts
     )