NTFS: Change ntfs_rl_truncate_nolock() to throw away the runlist if the new

      length is zero.
Signed-off-by: NAnton Altaparmakov <aia21@cantab.net>

fs/ntfs/ChangeLog

@@ -51,6 +51,8 @@ ToDo/Notes:
 	- Report unrepresentable inodes during ntfs_readdir() as KERN_WARNING
 	  messages and include the inode number.  Thanks to Yura Pakhuchiy for
 	  pointing this out.
+	- Change ntfs_rl_truncate_nolock() to throw away the runlist if the new
+	  length is zero.
 
 2.1.23 - Implement extension of resident files and make writing safe as well as
 	 many bug fixes, cleanups, and enhancements...

fs/ntfs/runlist.c

@@ -1455,6 +1455,7 @@ int ntfs_mapping_pairs_build(const ntfs_volume *vol, s8 *dst,
 
 /**
  * ntfs_rl_truncate_nolock - truncate a runlist starting at a specified vcn
+ * @vol:	ntfs volume (needed for error output)
  * @runlist:	runlist to truncate
  * @new_length:	the new length of the runlist in VCNs
  *
@@ -1462,12 +1463,16 @@ int ntfs_mapping_pairs_build(const ntfs_volume *vol, s8 *dst,
  * holding the runlist elements to a length of @new_length VCNs.
  *
  * If @new_length lies within the runlist, the runlist elements with VCNs of
- * @new_length and above are discarded.
+ * @new_length and above are discarded.  As a special case if @new_length is
+ * zero, the runlist is discarded and set to NULL.
  *
  * If @new_length lies beyond the runlist, a sparse runlist element is added to
  * the end of the runlist @runlist or if the last runlist element is a sparse
  * one already, this is extended.
  *
+ * Note, no checking is done for unmapped runlist elements.  It is assumed that
+ * the caller has mapped any elements that need to be mapped already.
+ *
  * Return 0 on success and -errno on error.
  *
  * Locking: The caller must hold @runlist->lock for writing.
@@ -1482,6 +1487,13 @@ int ntfs_rl_truncate_nolock(const ntfs_volume *vol, runlist *const runlist,
 	BUG_ON(!runlist);
 	BUG_ON(new_length < 0);
 	rl = runlist->rl;
+	if (!new_length) {
+		ntfs_debug("Freeing runlist.");
+		runlist->rl = NULL;
+		if (rl)
+			ntfs_free(rl);
+		return 0;
+	}
 	if (unlikely(!rl)) {
 		/*
 		 * Create a runlist consisting of a sparse runlist element of