[PATCH v20 02/12] Add infrastructure for copy offload in block and request layer.

[Keith Busch]

On Mon, Jun 24, 2024 at 04:14:07PM +0530, Nitesh Shetty wrote:
> c. List/ctx based approach:
> A new member is added to bio, bio_copy_ctx, which will a union with
> bi_integrity. Idea is once a copy bio reaches blk_mq_submit_bio, it will
> add the bio to this list.

Is there a reason to tie this to CONFIG_BLK_DEV_INTEGRITY? Why not use
the bio_io_vec? There's no user data here, so that's unused, right?

> 1. Send the destination BIO, once this reaches blk_mq_submit_bio, this
> will add the destination BIO to the list inside bi_copy_ctx and return
> without forming any request.
> 2. Send source BIO, once this reaches blk_mq_submit_bio, this will
> retrieve the destination BIO from bi_copy_ctx and form a request with
> destination BIO and source BIO. After this request will be sent to
> driver.

Like Damien, I also don't see the point of the 2-bio requirement. Treat
it like discard, and drivers can allocate "special".