[dm-devel] [PATCH 3/7] block: copy offload support infrastructure

[Bart Van Assche]

On 8/17/21 3:14 AM, SelvaKumar S wrote:
> Introduce REQ_OP_COPY, a no-merge copy offload operation. Create
> bio with control information as payload and submit to the device.
> Larger copy operation may be divided if necessary by looking at device
> limits. REQ_OP_COPY(19) is a write op and takes zone_write_lock when
> submitted to zoned device.
> Native copy offload is not supported for stacked devices.

Using a single operation for copy-offloading instead of separate 
operations for reading and writing is fundamentally incompatible with 
the device mapper. I think we need a copy-offloading implementation that 
is compatible with the device mapper.

Storing the parameters of the copy operation in the bio payload is 
incompatible with the current implementation of bio_split().

In other words, I think there are fundamental problems with this patch 
series.

Bart.