CA-373551: register for host events rather than task in events_from_xapi

A recent change registered for events on the task that was used by the
events_from_xapi thread in xapi_xenops. This is so that the event loop
can be woken up by injecting an event into this task, without the need
to logout its session (as previously done). The problem is that this
introduced a task in the DB that is forever "pending", which has
unwanted side-effects. For example, it gets GC'ed after 24 hours, and
also gets destroyed if the coordinator is restarted.

Switch to registering the host object for the localhost instead, which
should be more stable.

Signed-off-by: Rob Hoes <[email protected]>

ocaml/xapi/xapi_xenops.ml

@@ -3207,10 +3207,9 @@ end
 (* XXX: PR-1255: we also want to only listen for events on VMs and fields we care about *)
 let events_from_xapi () =
   let open Event_types in
-  Server_helpers.exec_with_new_task ~task_in_database:true "xapi events"
-    (fun __context ->
-      let task = Context.get_task_id __context |> Ref.string_of in
+  Server_helpers.exec_with_new_task "xapi events" (fun __context ->
       let localhost = Helpers.get_localhost ~__context in
+      let localhost' = Ref.string_of localhost in
       let token = ref "" in
       let stop = ref false in
       while not !stop do
@@ -3223,8 +3222,8 @@ let events_from_xapi () =
                       injection" ;
                    try
                      let _ =
-                       XenAPI.Event.inject ~rpc ~session_id ~_class:"task"
-                         ~_ref:task
+                       XenAPI.Event.inject ~rpc ~session_id ~_class:"host"
+                         ~_ref:localhost'
                      in
                      ()
                    with e ->
@@ -3252,7 +3251,7 @@ let events_from_xapi () =
                 error "events_from_xapi: extra items in the cache: [ %s ]"
                   (String.concat "; " (StringSet.elements extra_in_cache)) ;
               let classes =
-                Printf.sprintf "task/%s" task
+                Printf.sprintf "host/%s" localhost'
                 :: List.map
                      (fun x -> Printf.sprintf "VM/%s" (Ref.string_of x))
                      resident_VMs
@@ -3310,7 +3309,7 @@ let events_from_xapi () =
                             raise e
                           )
                       )
-                    | {ty= "task"; reference= t; _} when t = task ->
+                    | {ty= "host"; reference= t; _} when t = localhost' ->
                         debug
                           "Woken event thread: updating list of event \
                            subscriptions" ;