This provides a test driver and a set of test vectors for the page
alignment check callback function vdev_disk_check_pages_cb().
Because there's no good facility for exposing this function to a
userspace test right now, for now I'm just duplicating the function and
adding commentary to remind people to keep them in sync.
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
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