nilfs2: use device's backing_dev_info for btree node caches

Previously, default_backing_dev_info was used for the mapping of btree
node caches.  This uses device dependent backing_dev_info to allow
detailed control of the device for the btree node pages.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 6989b03..9acf30b 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -134,7 +134,7 @@
 
 static struct kmem_cache *nilfs_inode_cachep;
 
-struct inode *nilfs_alloc_inode(struct super_block *sb)
+struct inode *nilfs_alloc_inode_common(struct the_nilfs *nilfs)
 {
 	struct nilfs_inode_info *ii;
 
@@ -144,10 +144,15 @@
 	ii->i_bh = NULL;
 	ii->i_state = 0;
 	ii->vfs_inode.i_version = 1;
-	nilfs_btnode_cache_init(&ii->i_btnode_cache);
+	nilfs_btnode_cache_init(&ii->i_btnode_cache, nilfs->ns_bdi);
 	return &ii->vfs_inode;
 }
 
+struct inode *nilfs_alloc_inode(struct super_block *sb)
+{
+	return nilfs_alloc_inode_common(NILFS_SB(sb)->s_nilfs);
+}
+
 void nilfs_destroy_inode(struct inode *inode)
 {
 	kmem_cache_free(nilfs_inode_cachep, NILFS_I(inode));