Making DiskSpaceMonitorDescriptor public since it is hard to write a disk space monitor without it.

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

@@ -9,6 +9,7 @@ import java.util.logging.Logger;
 
 /**
  * @author Kohsuke Kawaguchi
+ * @see DiskSpaceMonitorDescriptor
  */
 public abstract class AbstractDiskSpaceMonitor extends NodeMonitor {
     /**

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

@@ -64,7 +64,7 @@ public class DiskSpaceMonitor extends AbstractDiskSpaceMonitor {
             return Messages.DiskSpaceMonitor_DisplayName();
         }
 
-        protected DiskSpace getFreeSpace(Computer c) throws IOException, InterruptedException {
+        @Override protected DiskSpace monitor(Computer c) throws IOException, InterruptedException {
             FilePath p = c.getNode().getRootPath();
             if(p==null) return null;
 

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

@@ -45,8 +45,9 @@ import org.kohsuke.stapler.export.Exported;
  * {@link AbstractNodeMonitorDescriptor} for {@link NodeMonitor} that checks a free disk space of some directory.
  *
  * @author Kohsuke Kawaguchi
+ * @since 1.520
 */
-/*package*/ abstract class DiskSpaceMonitorDescriptor extends AbstractNodeMonitorDescriptor<DiskSpace> {
+public abstract class DiskSpaceMonitorDescriptor extends AbstractNodeMonitorDescriptor<DiskSpace> {
     /**
      * Value object that represents the disk space.
      */
@@ -59,13 +60,6 @@ import org.kohsuke.stapler.export.Exported;
         private boolean triggered;
         private Class<? extends AbstractDiskSpaceMonitor> trigger;
 
-        /**
-         * @deprecated as of 1.467
-         */
-        public DiskSpace(long size) {
-            this(".",size);
-        }
-
         /**
          * @param path
          *      Specify the file path that was monitored.
@@ -165,15 +159,6 @@ import org.kohsuke.stapler.export.Exported;
         private static final long serialVersionUID = 2L;
     }
 
-    protected DiskSpace monitor(Computer c) throws IOException, InterruptedException {
-        return getFreeSpace(c);
-    }
-
-    /**
-     * Computes the free size.
-     */
-    protected abstract DiskSpace getFreeSpace(Computer c) throws IOException, InterruptedException;
-
     protected static final class GetUsableSpace implements FileCallable<DiskSpace> {
         @IgnoreJRERequirement
         public DiskSpace invoke(File f, VirtualChannel channel) throws IOException {

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

@@ -66,7 +66,7 @@ public class TemporarySpaceMonitor extends AbstractDiskSpaceMonitor {
             return Messages.TemporarySpaceMonitor_DisplayName();
         }
 
-        protected DiskSpace getFreeSpace(Computer c) throws IOException, InterruptedException {
+        @Override protected DiskSpace monitor(Computer c) throws IOException, InterruptedException {
             FilePath p = c.getNode().getRootPath();
             if(p==null) return null;