CA-423760: Retain host.last_update_hash on an ejected host (#6951)

Generally an ejected host can be considered as a fresh-installed one.
But in practice, the update level (the hash) is useful to determine the
update state of an ejected host.

One of the cases is a host was ejected from a pool. In this case, the
retained applied update hash is useful to determine if the host can join
the pool again easily.

Author: minglumlu

ocaml/xapi/dbsync_slave.ml

@@ -52,14 +52,21 @@ let create_localhost ~__context info =
   in
   (* me = None on firstboot only *)
   if me = None then
+    (* Restore the host.last_update_hash when this is an ejected host. *)
+    let last_update_hash =
+      let k = "last_update_hash" in
+      let x = Localdb.get k |> Option.value ~default:"" in
+      (try Localdb.del k with _ -> ()) ;
+      x
+    in
     let (_ : API.ref_host) =
       Xapi_host.create ~__context ~uuid:info.uuid ~name_label:info.hostname
         ~name_description:"" ~hostname:info.hostname ~address:ip
         ~external_auth_type:"" ~external_auth_service_name:""
         ~external_auth_configuration:[] ~license_params:[] ~edition:""
         ~license_server:[("address", "localhost"); ("port", "27000")]
         ~local_cache_sr:Ref.null ~chipset_info:[] ~ssl_legacy:false
-        ~last_software_update:Date.epoch ~last_update_hash:""
+        ~last_software_update:Date.epoch ~last_update_hash
         ~ssh_enabled:Constants.default_ssh_enabled
         ~ssh_enabled_timeout:Constants.default_ssh_enabled_timeout
         ~ssh_expiry:Date.epoch

ocaml/xapi/xapi_pool.ml

@@ -1963,6 +1963,7 @@ let eject_self ~__context ~host =
       (Db.Pool.get_current_operations ~__context ~self:pool)
   then
     raise Api_errors.(Server_error (not_supported_during_upgrade, [])) ;
+  let last_update_hash = Db.Host.get_last_update_hash ~__context ~self:host in
   if Pool_role.is_master () then
     raise Cannot_eject_master
   else (* Fail the operation if any VMs are running here (except dom0) *)
@@ -2093,6 +2094,8 @@ let eject_self ~__context ~host =
         pif.API.pIF_ipv6_configuration_mode
       |> String.uncapitalize_ascii
     in
+    Localdb.put "last_update_hash" last_update_hash ;
+    debug "Saved last_update_hash %S to localdb." last_update_hash ;
     let write_first_boot_management_interface_configuration_file () =
       (* During firstboot, now inventory has an empty MANAGEMENT_INTERFACE *)
       let bridge = "" in
@@ -3705,8 +3708,16 @@ let set_repositories ~__context ~self ~value =
     )
     value ;
   Db.Pool.set_repositories ~__context ~self ~value ;
-  if Db.Pool.get_repositories ~__context ~self = [] then
+  if Db.Pool.get_repositories ~__context ~self = [] then (
     Db.Pool.set_last_update_sync ~__context ~self ~value:Date.epoch ;
+    (* The host.latest_synced_updates_applied can't be refreshed by
+       pool.sync_updates. So reset it here. *)
+    Db.Host.get_all ~__context
+    |> List.iter (fun h ->
+        Db.Host.set_latest_synced_updates_applied ~__context ~self:h
+          ~value:`unknown
+    )
+  ) ;
   disable_unsupported_periodic_sync_updates ~__context ~self ~repos:value
 
 let add_repository ~__context ~self ~value =