dm_array_get_value
r = dm_array_get_value(&cmd->info, cmd->root, from_cblock(cblock), &value);
r = dm_array_get_value(&cmd->info, cmd->root, from_cblock(b), &value);
EXPORT_SYMBOL_GPL(dm_array_get_value);
int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
r = dm_array_get_value(&info->array_info, root, array_index, &value);