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

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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
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@xxxxxxx                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman




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