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>
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 40239a9..1bf695e 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -25,6 +25,7 @@
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
+#include <linux/random.h>
 #include <linux/crc32.h>
 #include "nilfs.h"
 #include "segment.h"
@@ -78,6 +79,7 @@
 	INIT_LIST_HEAD(&nilfs->ns_dirty_files);
 	INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
 	spin_lock_init(&nilfs->ns_inode_lock);
+	spin_lock_init(&nilfs->ns_next_gen_lock);
 	spin_lock_init(&nilfs->ns_last_segment_lock);
 	nilfs->ns_cptree = RB_ROOT;
 	spin_lock_init(&nilfs->ns_cptree_lock);
@@ -593,6 +595,9 @@
 	nilfs->ns_blocksize_bits = sb->s_blocksize_bits;
 	nilfs->ns_blocksize = blocksize;
 
+	get_random_bytes(&nilfs->ns_next_generation,
+			 sizeof(nilfs->ns_next_generation));
+
 	err = nilfs_store_disk_layout(nilfs, sbp);
 	if (err)
 		goto failed_sbh;