f2fs: introduce F2FS_I_SB, F2FS_M_SB, and F2FS_P_SB

This patch adds three inline functions to clean up dirty casting codes.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 155fb05..c242904 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -284,10 +284,9 @@
 
 int update_dent_inode(struct inode *inode, const struct qstr *name)
 {
-	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
 	struct page *page;
 
-	page = get_node_page(sbi, inode->i_ino);
+	page = get_node_page(F2FS_I_SB(inode), inode->i_ino);
 	if (IS_ERR(page))
 		return PTR_ERR(page);
 
@@ -337,7 +336,6 @@
 static struct page *init_inode_metadata(struct inode *inode,
 		struct inode *dir, const struct qstr *name)
 {
-	struct f2fs_sb_info *sbi = F2FS_SB(dir->i_sb);
 	struct page *page;
 	int err;
 
@@ -360,7 +358,7 @@
 		if (err)
 			goto put_error;
 	} else {
-		page = get_node_page(F2FS_SB(dir->i_sb), inode->i_ino);
+		page = get_node_page(F2FS_I_SB(dir), inode->i_ino);
 		if (IS_ERR(page))
 			return page;
 
@@ -381,7 +379,7 @@
 		 * we should remove this inode from orphan list.
 		 */
 		if (inode->i_nlink == 0)
-			remove_orphan_inode(sbi, inode->i_ino);
+			remove_orphan_inode(F2FS_I_SB(dir), inode->i_ino);
 		inc_nlink(inode);
 	}
 	return page;
@@ -571,8 +569,7 @@
 {
 	struct	f2fs_dentry_block *dentry_blk;
 	unsigned int bit_pos;
-	struct address_space *mapping = page->mapping;
-	struct inode *dir = mapping->host;
+	struct inode *dir = page->mapping->host;
 	int slots = GET_DENTRY_SLOTS(le16_to_cpu(dentry->name_len));
 	int i;
 
@@ -594,7 +591,7 @@
 	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
 
 	if (inode) {
-		struct f2fs_sb_info *sbi = F2FS_SB(dir->i_sb);
+		struct f2fs_sb_info *sbi = F2FS_I_SB(dir);
 
 		down_write(&F2FS_I(inode)->i_sem);