CA-416351: Slave shutdown timeout (#6645)

Before shutting down, xapi calls `xapi_pre_shutdown` to execute several
pre-shutdown scripts, which require the current host's UUID as a
parameter.

Currently, xapi obtains this UUID in a redundant manner:
1. It retrieves the UUID from the local inventory file.
2. It queries the database for the host's reference using the UUID.
3. It queries the database again for the host's UUID using the reference
obtained in step 2.

Steps 2 and 3 are unnecessary since the UUID is already available from
step 1. Moreover, when the master stops, the slave fails to query the
database, increasing xapi shutdown times on the slave.

The solution is to directly use the UUID obtained in step 1, eliminating
the redundant database queries.

Author: robhoes

ocaml/xapi/xapi_hooks.ml

@@ -102,22 +102,21 @@ let execute_hook ~__context ~script_name ~args ~reason =
       )
       scripts
 
-let execute_vm_hook ~__context ~reason ~vm =
-  let vmuuid = Db.VM.get_uuid ~__context ~self:vm in
-  execute_hook ~__context ~args:["-vmuuid"; vmuuid] ~reason
+let execute_vm_hook ~__context ~reason ~vm_uuid =
+  execute_hook ~__context ~args:["-vmuuid"; vm_uuid] ~reason
 
-let execute_host_hook ~__context ~reason ~host =
-  let uuid = Db.Host.get_uuid ~__context ~self:host in
-  execute_hook ~__context ~args:["-hostuuid"; uuid] ~reason
+let execute_host_hook ~__context ~reason ~host_uuid =
+  execute_hook ~__context ~args:["-hostuuid"; host_uuid] ~reason
 
 let execute_pool_hook ~__context ~reason =
   execute_hook ~__context ~args:[] ~reason
 
 let host_pre_declare_dead ~__context ~host ~reason =
   info "Running host pre declare dead hook for %s" (Ref.string_of host) ;
   (* this could use power fencing *)
+  let host_uuid = Db.Host.get_uuid ~__context ~self:host in
   execute_host_hook ~__context ~script_name:scriptname__host_pre_declare_dead
-    ~reason ~host ;
+    ~reason ~host_uuid ;
   if String.equal reason reason__dbdestroy then
     log_and_ignore_exn (fun () ->
         (* declare it as dead to the clustering daemon if any *)
@@ -132,11 +131,10 @@ let host_pre_declare_dead ~__context ~host ~reason =
             ()
     )
 
-let xapi_pre_shutdown ~__context ~host ~reason =
-  info "%s Running xapi pre shutdown hooks for %s" __FUNCTION__
-    (Ref.string_of host) ;
+let xapi_pre_shutdown ~__context ~host_uuid ~reason =
+  info "%s Running xapi pre shutdown hooks for %s" __FUNCTION__ host_uuid ;
   execute_host_hook ~__context ~script_name:scriptname__xapi_pre_shutdown
-    ~reason ~host
+    ~reason ~host_uuid
 
 (* Called when host died -- !! hook code in here to abort outstanding forwarded ops *)
 let internal_host_dead_hook __context host =
@@ -159,8 +157,9 @@ let internal_host_dead_hook __context host =
 let host_post_declare_dead ~__context ~host ~reason =
   (* Cancel outstanding tasks first-- should release necessary locks *)
   internal_host_dead_hook __context host ;
+  let host_uuid = Db.Host.get_uuid ~__context ~self:host in
   execute_host_hook ~__context ~script_name:scriptname__host_post_declare_dead
-    ~reason ~host
+    ~reason ~host_uuid
 
 let pool_ha_overcommitted_hook ~__context =
   execute_pool_hook ~__context ~script_name:scriptname__pool_ha_overcommitted

ocaml/xapi/xapi_host.ml

@@ -795,9 +795,9 @@ let restart_agent ~__context ~host:_ =
     )
 
 let shutdown_agent ~__context =
-  debug "Host.restart_agent: Host agent will shutdown in 1s!!!!" ;
-  let localhost = Helpers.get_localhost ~__context in
-  Xapi_hooks.xapi_pre_shutdown ~__context ~host:localhost
+  debug "Host.shutdown_agent: Host agent will shutdown in 1s!!!!" ;
+  let host_uuid = Helpers.get_localhost_uuid () in
+  Xapi_hooks.xapi_pre_shutdown ~__context ~host_uuid
     ~reason:Xapi_hooks.reason__clean_shutdown ;
   Xapi_fuse.light_fuse_and_dont_restart ~fuse_length:1. ()