+ return (get_capacity(bdev->bd_disk) << 9);
+}
+
+static void
+vdev_disk_error(zio_t *zio)
+{
+#ifdef ZFS_DEBUG
+ printk("ZFS: zio error=%d type=%d offset=%llu size=%llu "
+ "flags=%x delay=%llu\n", zio->io_error, zio->io_type,
+ (u_longlong_t)zio->io_offset, (u_longlong_t)zio->io_size,
+ zio->io_flags, (u_longlong_t)zio->io_delay);
+#endif
+}
+
+/*
+ * Use the Linux 'noop' elevator for zfs managed block devices. This
+ * strikes the ideal balance by allowing the zfs elevator to do all
+ * request ordering and prioritization. While allowing the Linux
+ * elevator to do the maximum front/back merging allowed by the
+ * physical device. This yields the largest possible requests for
+ * the device with the lowest total overhead.
+ *
+ * Unfortunately we cannot directly call the elevator_switch() function
+ * because it is not exported from the block layer. This means we have
+ * to use the sysfs interface and a user space upcall. Pools will be
+ * automatically imported on module load so we must do this at device
+ * open time from the kernel.
+ */
+#define SET_SCHEDULER_CMD \
+ "exec 0</dev/null " \
+ " 1>/sys/block/%s/queue/scheduler " \
+ " 2>/dev/null; " \
+ "echo %s"
+
+static int
+vdev_elevator_switch(vdev_t *v, char *elevator)
+{
+ vdev_disk_t *vd = v->vdev_tsd;
+ struct block_device *bdev = vd->vd_bdev;
+ struct request_queue *q = bdev_get_queue(bdev);
+ char *device = bdev->bd_disk->disk_name;
+ char *argv[] = { "/bin/sh", "-c", NULL, NULL };
+ char *envp[] = { NULL };
+ int error;
+
+ /* Skip devices which are not whole disks (partitions) */
+ if (!v->vdev_wholedisk)
+ return (0);
+
+ /* Skip devices without schedulers (loop, ram, dm, etc) */
+ if (!q->elevator || !blk_queue_stackable(q))
+ return (0);
+
+ /* Leave existing scheduler when set to "none" */
+ if (!strncmp(elevator, "none", 4) && (strlen(elevator) == 4))
+ return (0);
+
+ argv[2] = kmem_asprintf(SET_SCHEDULER_CMD, device, elevator);
+ error = call_usermodehelper(argv[0], argv, envp, 1);
+ if (error)
+ printk("ZFS: Unable to set \"%s\" scheduler for %s (%s): %d\n",
+ elevator, v->vdev_path, device, error);
+
+ strfree(argv[2]);
+
+ return (error);