Possible to create a custom AbstractDiskSpaceMonitor.

changelog.html

@@ -78,6 +78,8 @@ Upcoming changes</a>
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15380">issue 15380</a>)
   <li class=rfe>
     Added a new extension point to monitor the flow of stuff in the queue.
+  <li class=rfe>
+    Possible to create a custom <code>AbstractDiskSpaceMonitor</code>.
   <li class=rfe>
     Executors running the builds can be now a subject of access control.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18285">issue 18285</a>)

core/src/main/java/hudson/node_monitors/DiskSpaceMonitorDescriptor.java

@@ -160,6 +160,7 @@ public abstract class DiskSpaceMonitorDescriptor extends AbstractNodeMonitorDesc
     }
 
     protected static final class GetUsableSpace implements FileCallable<DiskSpace> {
+        public GetUsableSpace() {}
         @IgnoreJRERequirement
         public DiskSpace invoke(File f, VirtualChannel channel) throws IOException {
             try {