nilfs2: move next generation counter into nilfs object

Moves s_next_generation counter and a spinlock protecting it to nilfs
object from nilfs_sb_info structure.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/the_nilfs.h

@@ -74,6 +74,8 @@ enum {
  * @ns_dirty_files: list of dirty files
  * @ns_inode_lock: lock protecting @ns_dirty_files
  * @ns_gc_inodes: dummy inodes to keep live blocks
+ * @ns_next_generation: next generation number for inodes
+ * @ns_next_gen_lock: lock protecting @ns_next_generation
  * @ns_mount_opt: mount options
  * @ns_resuid: uid for reserved blocks
  * @ns_resgid: gid for reserved blocks
@@ -159,6 +161,10 @@ struct the_nilfs {
 	/* GC inode list */
 	struct list_head	ns_gc_inodes;
 
+	/* Inode allocator */
+	u32			ns_next_generation;
+	spinlock_t		ns_next_gen_lock;
+
 	/* Mount options */
 	unsigned long		ns_mount_opt;