Re: [PATCH v20 09/12] dm: Add support for copy offload

[Nitesh Shetty]

On 21/05/24 09:11AM, Hannes Reinecke wrote:
> On 5/20/24 12:20, Nitesh Shetty wrote:
> > Before enabling copy for dm target, check if underlying devices and
> > dm target support copy. Avoid split happening inside dm target.
> > Fail early if the request needs split, currently splitting copy
> > request is not supported.
> >
> > Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> > ---
> > @@ -397,6 +397,9 @@ struct dm_target {
> >  	 * bio_set_dev(). NOTE: ideally a target should _not_ need this.
> >  	 */
> >  	bool needs_bio_set_dev:1;
> > +
> > +	/* copy offload is supported */
> > +	bool copy_offload_supported:1;
> >  };
> >  void *dm_per_bio_data(struct bio *bio, size_t data_size);
>
> Errm. Not sure this will work. DM tables might be arbitrarily, 
> requiring us to _split_ the copy offload request according to the 
> underlying component devices. But we explicitly disallowed a split in 
> one of the earlier patches.
> Or am I wrong?
Yes you are right w.r.to split, we disallow split.
But this flag indicates whether we support copy offload in dm-target or
not. At present we support copy offload only in dm-linear.
For other dm-target, eventhough underlaying device supports copy
offload, dm-target based on it wont support copy offload.
If the present series get merged, we can test and integrate more
targets.

Regards,
Nitesh Shetty