+/*
+ * This function is grabs code from the very beginning of
+ * ext4_map_blocks, but assumes that the caller is from delayed write
+ * time. This function looks up the requested blocks and sets the
+ * buffer delay bit under the protection of i_data_sem.
+ */
+static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
+ struct ext4_map_blocks *map,
+ struct buffer_head *bh)
+{
+ int retval;
+ sector_t invalid_block = ~((sector_t) 0xffff);
+
+ if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
+ invalid_block = ~0;
+
+ map->m_flags = 0;
+ ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
+ "logical block %lu\n", inode->i_ino, map->m_len,
+ (unsigned long) map->m_lblk);
+ /*
+ * Try to see if we can get the block without requesting a new
+ * file system block.
+ */
+ down_read((&EXT4_I(inode)->i_data_sem));
+ if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+ retval = ext4_ext_map_blocks(NULL, inode, map, 0);
+ else
+ retval = ext4_ind_map_blocks(NULL, inode, map, 0);
+
+ if (retval == 0) {
+ /*
+ * XXX: __block_prepare_write() unmaps passed block,
+ * is it OK?
+ */
+ /* If the block was allocated from previously allocated cluster,
+ * then we dont need to reserve it again. */
+ if (!(map->m_flags & EXT4_MAP_FROM_CLUSTER)) {
+ retval = ext4_da_reserve_space(inode, iblock);
+ if (retval)
+ /* not enough space to reserve */
+ goto out_unlock;
+ }
+
+ /* Clear EXT4_MAP_FROM_CLUSTER flag since its purpose is served
+ * and it should not appear on the bh->b_state.
+ */
+ map->m_flags &= ~EXT4_MAP_FROM_CLUSTER;
+
+ map_bh(bh, inode->i_sb, invalid_block);
+ set_buffer_new(bh);
+ set_buffer_delay(bh);
+ }
+
+out_unlock:
+ up_read((&EXT4_I(inode)->i_data_sem));
+
+ return retval;
+}
+