Re: [PATCH v6 3/9] block: add emulation for copy

[Hannes Reinecke]

On 1/12/23 12:58, Nitesh Shetty wrote:
> For the devices which does not support copy, copy emulation is
> added. Copy-emulation is implemented by reading from source ranges
> into memory and writing to the corresponding destination asynchronously.
> For zoned device we maintain a linked list of read submission and try to
> submit corresponding write in same order.
> Also emulation is used, if copy offload fails or partially completes.
>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> Signed-off-by: Vincent Fu <vincent.fu@xxxxxxxxxxx>
> Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
> ---
>   block/blk-lib.c        | 241 ++++++++++++++++++++++++++++++++++++++++-
>   block/blk-map.c        |   4 +-
>   include/linux/blkdev.h |   3 +
>   3 files changed, 245 insertions(+), 3 deletions(-)
I'm not sure if I agree with this one.

You just submitted a patch for device-mapper to implement copy offload, 
which (to all intents and purposes) _is_ an emulation.

So why do we need to implement it in the block layer as an emulation?
Or, if we have to, why do we need the device-mapper emulation?
This emulation will be doing the same thing, no?

Cheers,

Hannes