UBIFS: introduce LEB overhead

This is a preparational patch for the following statfs()
report fix.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -530,6 +530,12 @@ static int init_constants_early(struct ubifs_info *c)
 	c->dead_wm = ALIGN(MIN_WRITE_SZ, c->min_io_size);
 	c->dark_wm = ALIGN(UBIFS_MAX_NODE_SZ, c->min_io_size);
 
+	/*
+	 * Calculate how many bytes would be wasted at the end of LEB if it was
+	 * fully filled with data nodes of maximum size. This is used in
+	 * calculations when reporting free space.
+	 */
+	c->leb_overhead = c->leb_size % UBIFS_MAX_DATA_NODE_SZ;
 	return 0;
 }
 

fs/ubifs/ubifs.h

@@ -995,6 +995,9 @@ struct ubifs_mount_opts {
  * @max_idx_node_sz: maximum indexing node aligned on 8-bytes boundary
  * @max_inode_sz: maximum possible inode size in bytes
  * @max_znode_sz: size of znode in bytes
+ *
+ * @leb_overhead: how many bytes are wasted in an LEB when it is filled with
+ *                data nodes of maximum size - used in free space reporting
  * @dead_wm: LEB dead space watermark
  * @dark_wm: LEB dark space watermark
  * @block_cnt: count of 4KiB blocks on the FS
@@ -1226,6 +1229,8 @@ struct ubifs_info {
 	int max_idx_node_sz;
 	long long max_inode_sz;
 	int max_znode_sz;
+
+	int leb_overhead;
 	int dead_wm;
 	int dark_wm;
 	int block_cnt;