CP-13493: Thread to update xapi db for physical utilisation of SR

1) This new thread will run on each host.
2) Thread will update physical utilisation only for SR
which has SR_STATS capability and sr-master.

Signed-off-by: Sharad Yadav <[email protected]>

Author: sharady

ocaml/xapi/xapi.ml

@@ -960,6 +960,7 @@ let server_init() =
       "writing init complete", [], (fun () -> Helpers.touch_file !Xapi_globs.init_complete);
 (*      "Synchronising HA state with Pool", [ Startup.NoExnRaising ], Xapi_ha.synchronise_ha_state_with_pool; *)
 			"Starting DR redo-logs", [ Startup.OnlyMaster; ], start_dr_redo_logs;
+			"Starting SR physical utilisation scanning", [Startup.OnThread], (Xapi_sr.physical_utilisation_thread ~__context);
 			"Caching metadata VDIs created by foreign pools.", [ Startup.OnlyMaster; ], cache_metadata_vdis;
 			"Stats reporting thread", [], Xapi_stats.start;
     ];

ocaml/xapi/xapi_sr.ml

@@ -124,6 +124,33 @@ let scanning_thread () = Debug.with_thread_named "scanning_thread" (fun () ->
 		done)
 	) ()
 
+let sr_cache = ref []
+
+let update_physical_utilisation ~__context =
+	let srs = Helpers.get_all_plugged_srs ~__context in
+	(* Remove SRs from sr_cache if they are no more available *)
+	sr_cache := List.filter (fun sr -> (List.mem sr srs)) !sr_cache;
+	(* Checks whether SR is sr_master and has SR_STATS capability *)
+	let is_stats_sr ~__context sr =
+		let sr_record = Db.SR.get_record_internal ~__context ~self:sr in
+		if (Smint.(has_capability Sr_stats (Xapi_sr_operations.features_of_sr ~__context sr_record)) &&
+			(Helpers.i_am_srmaster ~__context ~sr))
+			then true else false
+	in
+	let srs_to_be_added = List.filter (fun sr -> (List.mem sr !sr_cache = false) && (is_stats_sr ~__context sr)) srs in
+	sr_cache := !sr_cache @ srs_to_be_added;
+	(* Update the physical utilisation db field of cached SRs *)
+	List.iter (fun sr ->
+		let new_value = Rrdd.query_sr_ds ~sr_uuid:(Db.SR.get_uuid ~__context ~self:sr) ~ds_name:"physical_utilisation" in
+		Db.SR.set_physical_utilisation ~__context ~self:sr ~value:(Int64.of_float new_value)) !sr_cache
+
+let physical_utilisation_thread ~__context () =
+	while true do
+		Thread.delay 120. ;
+		try update_physical_utilisation ~__context
+		with e -> debug "Exception in SR physical utilisation scanning thread: %s" (Printexc.to_string e)
+	done
+
 (* introduce, creates a record for the SR in the database. It has no other side effect *)
 let introduce  ~__context ~uuid ~name_label
 		~name_description ~_type ~content_type ~shared ~sm_config =