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

[Nitesh Shetty]

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

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