[dm-devel] [PATCH v2 05/10] block: add emulation for copy

[Mikulas Patocka]

On Mon, 7 Feb 2022, Nitesh Shetty wrote:

> +				goto retry;
> +			return PTR_ERR(bio);
> +		}
> +
> +		bio->bi_iter.bi_sector = sector >> SECTOR_SHIFT;
> +		bio->bi_opf = op;
> +		bio_set_dev(bio, bdev);
> @@ -346,6 +463,8 @@ int blkdev_issue_copy(struct block_device *src_bdev, int nr,
>  
>  	if (blk_check_copy_offload(src_q, dest_q))
>  		ret = blk_copy_offload(src_bdev, nr, rlist, dest_bdev, gfp_mask);
> +	else
> +		ret = blk_copy_emulate(src_bdev, nr, rlist, dest_bdev, gfp_mask);
>  
>  	return ret;
>  }

The emulation is not reliable because a device mapper device may be 
reconfigured and it may lose the copy capability between the calls to 
blk_check_copy_offload and blk_copy_offload.

You should call blk_copy_emulate if blk_copy_offload returns an error.

Mikulas