Re: [PATCH v15 02/12] Add infrastructure for copy offload in block and request layer.

[Hannes Reinecke]

On 9/6/23 18:38, Nitesh Shetty wrote:
> We add two new opcode REQ_OP_COPY_SRC, REQ_OP_COPY_DST.
> Since copy is a composite operation involving src and dst sectors/lba,
> each needs to be represented by a separate bio to make it compatible
> with device mapper.
> We expect caller to take a plug and send bio with source information,
> followed by bio with destination information.
> Once the src bio arrives we form a request and wait for destination
> bio. Upon arrival of destination we merge these two bio's and send
> corresponding request down to device driver.
>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
> ---
>   block/blk-core.c          |  7 +++++++
>   block/blk-merge.c         | 41 +++++++++++++++++++++++++++++++++++++++
>   block/blk.h               | 16 +++++++++++++++
>   block/elevator.h          |  1 +
>   include/linux/bio.h       |  6 +-----
>   include/linux/blk_types.h | 10 ++++++++++
>   6 files changed, 76 insertions(+), 5 deletions(-)
Having two separate bios is okay, and what one would expect.
What is slightly strange is the merging functionality;
That could do with some more explanation why this approach was taken.
And also some checks in the merging code to avoid merging non-copy 
offload  bios.

Cheers,

Hannes
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Dr. Hannes Reinecke                Kernel Storage Architect
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