On Wed, Feb 16, 2022 at 08:32:45AM -0500, Mikulas Patocka wrote:

On Mon, 7 Feb 2022, Nitesh Shetty wrote:

quoted

+				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

I agree, it was in our todo list to fallback to emulation for partial
copy offload failures. In next version we will add this.

--
Nitesh Shetty