NFS: Add a client-side function to display NFS file handles

For debugging, introduce a simplistic function to print NFS file
handles on the system console.  The main function is hooked into the
dprintk debugging facility, but you can directly call the helper,
_nfs_display_fhandle(), if you want to print a handle unconditionally.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_fs.h

@@ -395,6 +395,20 @@ static inline void nfs_free_fhandle(const struct nfs_fh *fh)
 	kfree(fh);
 }
 
+#ifdef RPC_DEBUG
+extern void _nfs_display_fhandle(const struct nfs_fh *fh, const char *caption);
+#define nfs_display_fhandle(fh, caption)			\
+	do {							\
+		if (unlikely(nfs_debug & NFSDBG_FACILITY))	\
+			_nfs_display_fhandle(fh, caption);	\
+	} while (0)
+#else
+static inline void nfs_display_fhandle(const struct nfs_fh *fh,
+				       const char *caption)
+{
+}
+#endif
+
 /*
  * linux/fs/nfs/nfsroot.c
  */