Function zio_change_priority

freebsd/contrib/openzfs/module/zfs/zio.c:3892–3912

* This function is used to change the priority of an existing zio that is * currently in-flight. This is used by the arc to upgrade priority in the * event that a demand read is made for a block that is currently queued * as a scrub or async read IO. Otherwise, the high priority read request * would end up having to wait for the lower priority IO. */

 * would end up having to wait for the lower priority IO.
 */
void
zio_change_priority(zio_t *pio, zio_priority_t priority)
{
	zio_t *cio, *cio_next;
	zio_link_t *zl = NULL;

	ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);

	if (pio->io_vd != NULL && pio->io_vd->vdev_ops->vdev_op_leaf) {
		vdev_queue_change_io_priority(pio, priority);
	} else {
		pio->io_priority = priority;
	}

	mutex_enter(&pio->io_lock);
	for (cio = zio_walk_children(pio, &zl); cio != NULL; cio = cio_next) {
		cio_next = zio_walk_children(pio, &zl);
		zio_change_priority(cio, priority);
	}
	mutex_exit(&pio->io_lock);
}

/*
 * For non-raidz ZIOs, we can just copy aside the bad data read from the