nilfs2: get rid of nilfs_sb_info structure

This directly uses sb->s_fs_info to keep a nilfs filesystem object and
fully removes the intermediate nilfs_sb_info structure.  With this
change, the hierarchy of on-memory structures of nilfs will be
simplified as follows:

Before:
  super_block
       -> nilfs_sb_info
             -> the_nilfs
                   -> cptree --+-> nilfs_root (current file system)
                               +-> nilfs_root (snapshot A)
                               +-> nilfs_root (snapshot B)
                               :
             -> nilfs_sc_info (log writer structure)
After:
  super_block
       -> the_nilfs
             -> cptree --+-> nilfs_root (current file system)
                         +-> nilfs_root (snapshot A)
                         +-> nilfs_root (snapshot B)
                         :
             -> nilfs_sc_info (log writer structure)

The reason why we didn't design so from the beginning is because the
initial shape also differed from the above.  The early hierachy was
composed of "per-mount-point" super_block -> nilfs_sb_info pairs and a
shared nilfs object.  On the kernel 2.6.37, it was changed to the
current shape in order to unify super block instances into one per
device, and this cleanup became applicable as the result.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 7a3dbe4..d5625be 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -295,7 +295,7 @@
 struct inode *nilfs_new_inode(struct inode *dir, int mode)
 {
 	struct super_block *sb = dir->i_sb;
-	struct the_nilfs *nilfs = NILFS_SB(sb)->s_nilfs;
+	struct the_nilfs *nilfs = sb->s_fs_info;
 	struct inode *inode;
 	struct nilfs_inode_info *ii;
 	struct nilfs_root *root;
@@ -433,7 +433,7 @@
 			      struct nilfs_root *root, unsigned long ino,
 			      struct inode *inode)
 {
-	struct the_nilfs *nilfs = NILFS_SB(sb)->s_nilfs;
+	struct the_nilfs *nilfs = sb->s_fs_info;
 	struct buffer_head *bh;
 	struct nilfs_inode *raw_inode;
 	int err;
@@ -807,7 +807,7 @@
 
 int nilfs_load_inode_block(struct inode *inode, struct buffer_head **pbh)
 {
-	struct the_nilfs *nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
+	struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
 	struct nilfs_inode_info *ii = NILFS_I(inode);
 	int err;
 
@@ -836,7 +836,7 @@
 int nilfs_inode_dirty(struct inode *inode)
 {
 	struct nilfs_inode_info *ii = NILFS_I(inode);
-	struct the_nilfs *nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
+	struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
 	int ret = 0;
 
 	if (!list_empty(&ii->i_dirty)) {
@@ -851,7 +851,7 @@
 int nilfs_set_file_dirty(struct inode *inode, unsigned nr_dirty)
 {
 	struct nilfs_inode_info *ii = NILFS_I(inode);
-	struct the_nilfs *nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
+	struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
 
 	atomic_add(nr_dirty, &nilfs->ns_ndirtyblks);