f2fs_reserve_block
err = f2fs_reserve_block(&dn, index);
err = f2fs_reserve_block(dn, index);
err = f2fs_reserve_block(&dn, index);
err = f2fs_reserve_block(&dn, index);
int f2fs_reserve_block(struct dnode_of_data *dn, pgoff_t index);
err = f2fs_reserve_block(dn, 0);
err = f2fs_reserve_block(&dn, 0);