[PATCH v2 08/10] dm: Add support for copy offload.

[Mikulas Patocka]

On Thu, 24 Feb 2022, Nitesh Shetty wrote:

> On Wed, Feb 16, 2022 at 08:51:08AM -0500, Mikulas Patocka wrote:
> > 
> > 
> > On Mon, 7 Feb 2022, Nitesh Shetty wrote:
> > 
> > > Before enabling copy for dm target, check if underlaying devices and
> > > dm target support copy. Avoid split happening inside dm target.
> > > Fail early if the request needs split, currently spliting copy
> > > request is not supported
> > > 
> > > Signed-off-by: Nitesh Shetty <nj.shetty at samsung.com>
> > 
> > If a dm device is reconfigured, you must invalidate all the copy tokens 
> > that are in flight, otherwise they would copy stale data.
> > 
> > I suggest that you create a global variable "atomic64_t dm_changed".
> > In nvme_setup_copy_read you copy this variable to the token.
> > In nvme_setup_copy_write you compare the variable with the value in the 
> > token and fail if there is mismatch.
> > In dm.c:__bind you increase the variable, so that all the tokens will be 
> > invalidated if a dm table is changed.
> > 
> > Mikulas
> > 
> >
> Yes, you are right about the reconfiguration of dm device. But wouldn't having a
> single global counter(dm_changed), will invalidate for all in-flight copy IO's
> across all dm devices. Is my understanding correct?
> 
> --
> Nitesh Shetty

Yes, changing it will invalidate all the copy IO's.

But invalidating only IO's affected by the table reload would be hard to 
achieve.

Mikulas