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

[Mikulas Patocka]

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