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

[Christoph Hellwig]

On Thu, May 30, 2024 at 10:11:15AM -0700, Bart Van Assche wrote:
> This new approach has the following two disadvantages:
> * Without plug, REQ_OP_COPY_SRC and REQ_OP_COPY_DST are not combined. These two
>   operation types are the only operation types for which not using a plug causes
>   an I/O failure.

So?  We can clearly document that and even fail submission with a helpful
message trivially to enforce that.

> * A loop is required to combine the REQ_OP_COPY_SRC and REQ_OP_COPY_DST operations.

I don't see why that is a problem.  Especiallly once we allow multiple
sources which is really useful for GC workloads we'll need to do that
anyway.

> Please switch to the approach Hannes suggested, namely bio chaining. Chaining
> REQ_OP_COPY_SRC and REQ_OP_COPY_DST bios before these are submitted eliminates the
> two disadvantages mentioned above.

No.