[PATCH v2 12/20] block,nvme,scsi,dm: Add blk_status to pr_ops callouts.

[Christoph Hellwig]

On Mon, Aug 08, 2022 at 07:04:11PM -0500, Mike Christie wrote:
> To handle both cases, this patch adds a blk_status_t arg to the pr_ops
> callouts. The lower levels will convert their device specific error to
> the blk_status_t then the upper levels can easily check that code
> without knowing the device type. It also allows us to keep userspace
> compat where it expects a negative -Exyz error code if the command fails
> before it's sent to the device or a device/tranport specific value if the
> error is > 0.

Why do we need two return values here?