namespace: add nlink as an attribute

Motivation:

It is occationally useful to know when deleting a file will trigger
garbage collection of the underlying data storage.  For files, this
happens when the file has an nlink count of 1.

Modification:

Add nlink as a file attribute.

Result:

The nlink count of a file is available when querying a file.

Target: master
Requires-notes: no
Requires-book: no
Patch: https://rb.dcache.org/r/9693/
Acked-by: Gerd Behrmann

modules/dcache-chimera/src/main/java/org/dcache/chimera/namespace/ChimeraNameSpaceProvider.java

@@ -873,6 +873,10 @@ private FileAttributes getFileAttributes(ExtendedInode inode, Set<FileAttribute>
                     attributes.setHsm(storageInfo.getHsm());
                 }
                 break;
+            case NLINK:
+                stat = inode.statCache();
+                attributes.setNlink(stat.getNlink());
+                break;
             default:
                 throw new UnsupportedOperationException("Attribute " + attribute + " not supported yet.");
             }

modules/dcache-vehicles/src/main/java/org/dcache/namespace/FileAttribute.java

@@ -28,5 +28,10 @@ public enum FileAttribute {
     STORAGEINFO,
     TYPE,
     SIMPLE_TYPE,
-    PNFSID
+    PNFSID,
+
+    /**
+     * @since 2.17
+     */
+    NLINK   // Be careful not to send this to pools before next golden release
 }

modules/dcache-vehicles/src/main/java/org/dcache/vehicles/FileAttributes.java

@@ -111,6 +111,11 @@ public class FileAttributes implements Serializable {
      */
     private int _mode;
 
+    /**
+     * @since 2.17
+     */
+    private int _nlink;
+
     /**
      * file's access latency ( e.g. ONLINE/NEARLINE )
      */
@@ -473,6 +478,18 @@ public String getHsm()
         return _hsm;
     }
 
+    public void setNlink(int nlink)
+    {
+        define(NLINK);
+        _nlink = nlink;
+    }
+
+    public int getNlink()
+    {
+        guard(NLINK);
+        return _nlink;
+    }
+
     @Override
     public String toString()
     {