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

[Hannes Reinecke]

On 5/21/24 16:08, Nitesh Shetty wrote:
> 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.
But dm-linear can be concatenated, too; you can easily use dm-linear
to tie several devices together.
Which again would require a copy-offload range to be split.
Hmm?

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich