f2fs: add a new function: f2fs_reserve_block()

Add the function f2fs_reserve_block() to easily reserve new blocks, and
use it to clean up more codes.

Signed-off-by: Huajun Li <huajun.li@intel.com>
Signed-off-by: Haicheng Li <haicheng.li@linux.intel.com>
Signed-off-by: Weihong Xu <weihong.xu@intel.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 417280a..c8eb37e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1130,6 +1130,7 @@
  * data.c
  */
 int reserve_new_block(struct dnode_of_data *);
+int f2fs_reserve_block(struct dnode_of_data *, pgoff_t);
 void update_extent_cache(block_t, struct dnode_of_data *);
 struct page *find_data_page(struct inode *, pgoff_t, bool);
 struct page *get_lock_data_page(struct inode *, pgoff_t);