CA-412636: hostname changed to localhost with static IP and reboot (#6546)

According to
https://www.freedesktop.org/software/systemd/man/latest/hostname.html
Systemd set hostname with following sequence
- kernel parameter, systemd.hostname
- static hostname in /etc/hostname
- transient hostname like DHCP
- localhost at systemd compile time

Once the host is configured with static IP and reboot, it would just
lost its hostname as no DHCP or static IP available.

However, the hostname is critical to AD function as it construct the
machine account.

The hostname should be persisted as static name during joining AD, this
is also what PBIS does.

Note: the static hostname is not cleaned during domain leave. This is by
intention to avoid losing hostname after reboot with static IP

cba2f1d tried to resovle the issue and
update /etc/resolv.conf However, /etc/resolv.conf does not help and
conflict with xcp-networkd, as networkd override the configure every 5
minutes Here we just revert the resolv.conf update

Author: liulinC

ocaml/xapi/extauth_plugin_ADwinbind.ml

@@ -1434,23 +1434,6 @@ module ConfigHosts = struct
     |> write_string_to_file path
 end
 
-module ResolveConfig = struct
-  let path = "/etc/resolv.conf"
-
-  type t = Add | Remove
-
-  let handle op domain =
-    let open Xapi_stdext_unix.Unixext in
-    let config = Printf.sprintf "search %s" domain in
-    read_lines ~path |> List.filter (fun x -> x <> config) |> fun x ->
-    (match op with Add -> config :: x | Remove -> x) |> fun x ->
-    x @ [""] |> String.concat "\n" |> write_string_to_file path
-
-  let join ~domain = handle Add domain
-
-  let leave ~domain = handle Remove domain
-end
-
 module DNSSync = struct
   let task_name = "Sync hostname with DNS"
 
@@ -1827,7 +1810,11 @@ module AuthADWinbind : Auth_signature.AUTH_MODULE = struct
       ClosestKdc.trigger_update ~start:0. ;
       RotateMachinePassword.trigger_rotate ~start:0. ;
       ConfigHosts.join ~domain:service_name ~name:netbios_name ;
-      ResolveConfig.join ~domain:service_name ;
+      let _, _ =
+        Forkhelpers.execute_command_get_output !Xapi_globs.set_hostname
+          [get_localhost_name ()]
+      in
+      (* Trigger right now *)
       DNSSync.trigger_sync ~start:0. ;
       Winbind.set_machine_account_encryption_type netbios_name ;
       debug "Succeed to join domain %s" service_name
@@ -1836,15 +1823,13 @@ module AuthADWinbind : Auth_signature.AUTH_MODULE = struct
         error "Join domain: %s error: %s" service_name stdout ;
         clear_winbind_config () ;
         ConfigHosts.leave ~domain:service_name ~name:netbios_name ;
-        ResolveConfig.leave ~domain:service_name ;
         (* The configure is kept for debug purpose with max level *)
         raise (Auth_service_error (stdout |> tag_from_err_msg, stdout))
     | Xapi_systemctl.Systemctl_fail _ ->
         let msg = Printf.sprintf "Failed to start %s" Winbind.name in
         error "Start daemon error: %s" msg ;
         config_winbind_daemon ~domain:None ~workgroup:None ~netbios_name:None ;
         ConfigHosts.leave ~domain:service_name ~name:netbios_name ;
-        ResolveConfig.leave ~domain:service_name ;
         raise (Auth_service_error (E_GENERIC, msg))
     | e ->
         let msg =
@@ -1856,7 +1841,6 @@ module AuthADWinbind : Auth_signature.AUTH_MODULE = struct
         error "Enable extauth error: %s" msg ;
         clear_winbind_config () ;
         ConfigHosts.leave ~domain:service_name ~name:netbios_name ;
-        ResolveConfig.leave ~domain:service_name ;
         raise (Auth_service_error (E_GENERIC, msg))
 
   (* unit on_disable()
@@ -1871,7 +1855,6 @@ module AuthADWinbind : Auth_signature.AUTH_MODULE = struct
     let user = List.assoc_opt "user" config_params in
     let pass = List.assoc_opt "pass" config_params in
     let {service_name; netbios_name; _} = get_domain_info_from_db () in
-    ResolveConfig.leave ~domain:service_name ;
     DNSSync.stop_sync () ;
     ( match netbios_name with
     | Some netbios ->