CA-86883: Detach SR if SR.destroy fails

The storage backend can destroy an SR only if it is attached.
Therefore when xapi wants to destroy an SR, first it attaches it.
When the backend destroys the SR it is no longer attached.

This change adds exception handling so that if the backend fails
to destroy the SR, xapi will detach it.

Author: thomassa

ocaml/xapi/storage_access.ml

@@ -1151,8 +1151,15 @@ let destroy_sr ~__context ~sr =
 			Client.SR.attach dbg (Db.SR.get_uuid ~__context ~self:sr) pbd_t.API.pBD_device_config;
 			(* The current backends expect the PBD to be temporarily set to currently_attached = true *)
 			Db.PBD.set_currently_attached ~__context ~self:pbd ~value:true;
-			Pervasiveext.finally (fun () ->
-				Client.SR.destroy dbg (Db.SR.get_uuid ~__context ~self:sr))
+			Pervasiveext.finally
+				(fun () ->
+					try
+						Client.SR.destroy dbg (Db.SR.get_uuid ~__context ~self:sr)
+					with exn ->
+						(* Clean up: SR is left attached if destroy fails *)
+						Client.SR.detach dbg (Db.SR.get_uuid ~__context ~self:sr);
+						raise exn
+				)
 				(fun () -> 
 					(* All PBDs are clearly currently_attached = false now *)
 					Db.PBD.set_currently_attached ~__context ~self:pbd ~value:false);