f2fs: introduce f2fs_map_bh to clean codes of check_extent_cache

This patch introduces f2fs_map_bh to clean codes of check_extent_cache.

v2:
 o cleanup f2fs_map_bh pointed out by Jaegeuk Kim.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -248,8 +248,23 @@ int f2fs_reserve_block(struct dnode_of_data *dn, pgoff_t index)
 	return err;
 }
 
+static void f2fs_map_bh(struct super_block *sb, pgoff_t pgofs,
+			struct extent_info *ei, struct buffer_head *bh_result)
+{
+	unsigned int blkbits = sb->s_blocksize_bits;
+	size_t count;
+
+	set_buffer_new(bh_result);
+	map_bh(bh_result, sb, ei->blk + pgofs - ei->fofs);
+	count = ei->fofs + ei->len - pgofs;
+	if (count < (UINT_MAX >> blkbits))
+		bh_result->b_size = (count << blkbits);
+	else
+		bh_result->b_size = UINT_MAX;
+}
+
 static int check_extent_cache(struct inode *inode, pgoff_t pgofs,
-					struct buffer_head *bh_result)
+					struct extent_info *ei)
 {
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 	pgoff_t start_fofs, end_fofs;
@@ -271,18 +286,7 @@ static int check_extent_cache(struct inode *inode, pgoff_t pgofs,
 	start_blkaddr = fi->ext.blk;
 
 	if (pgofs >= start_fofs && pgofs <= end_fofs) {
-		unsigned int blkbits = inode->i_sb->s_blocksize_bits;
-		size_t count;
-
-		set_buffer_new(bh_result);
-		map_bh(bh_result, inode->i_sb,
-				start_blkaddr + pgofs - start_fofs);
-		count = end_fofs - pgofs + 1;
-		if (count < (UINT_MAX >> blkbits))
-			bh_result->b_size = (count << blkbits);
-		else
-			bh_result->b_size = UINT_MAX;
-
+		*ei = fi->ext;
 		stat_inc_read_hit(inode->i_sb);
 		read_unlock(&fi->ext_lock);
 		return 1;
@@ -658,13 +662,16 @@ static int __get_data_block(struct inode *inode, sector_t iblock,
 	int mode = create ? ALLOC_NODE : LOOKUP_NODE_RA;
 	pgoff_t pgofs, end_offset;
 	int err = 0, ofs = 1;
+	struct extent_info ei;
 	bool allocated = false;
 
 	/* Get the page offset from the block offset(iblock) */
 	pgofs =	(pgoff_t)(iblock >> (PAGE_CACHE_SHIFT - blkbits));
 
-	if (check_extent_cache(inode, pgofs, bh_result))
+	if (check_extent_cache(inode, pgofs, &ei)) {
+		f2fs_map_bh(inode->i_sb, pgofs, &ei, bh_result);
 		goto out;
+	}
 
 	if (create)
 		f2fs_lock_op(F2FS_I_SB(inode));