slot_store(struct md_rdev *rdev, const char *buf, size_t len)
{
	int slot;
	int err;

	if (strncmp(buf, "none", 4)==0)
		slot = -1;
	else {
		err = kstrtouint(buf, 10, (unsigned int *)&slot);
		if (err < 0)
			return err;
	}
	if (rdev->mddev->pers && slot == -1) {
		/* Setting 'slot' on an active array requires also
		 * updating the 'rd%d' link, and communicating
		 * with the personality with ->hot_*_disk.
		 * For now we only support removing
		 * failed/spare devices.  This normally happens automatically,
		 * but not when the metadata is externally managed.
		 */
		if (rdev->raid_disk == -1)
			return -EEXIST;
		/* personality does all needed checks */
		if (rdev->mddev->pers->hot_remove_disk == NULL)
			return -EINVAL;
		clear_bit(Blocked, &rdev->flags);
		remove_and_add_spares(rdev->mddev, rdev);
		if (rdev->raid_disk >= 0)
			return -EBUSY;
		set_bit(MD_RECOVERY_NEEDED, &rdev->mddev->recovery);
		md_wakeup_thread(rdev->mddev->thread);
	} else if (rdev->mddev->pers) {
		/* Activating a spare .. or possibly reactivating
		 * if we ever get bitmaps working here.
		 */

		if (rdev->raid_disk != -1)
			return -EBUSY;

		if (test_bit(MD_RECOVERY_RUNNING, &rdev->mddev->recovery))
			return -EBUSY;

		if (rdev->mddev->pers->hot_add_disk == NULL)
			return -EINVAL;

		if (slot >= rdev->mddev->raid_disks &&
		    slot >= rdev->mddev->raid_disks + rdev->mddev->delta_disks)
			return -ENOSPC;

		rdev->raid_disk = slot;
		if (test_bit(In_sync, &rdev->flags))
			rdev->saved_raid_disk = slot;
		else
			rdev->saved_raid_disk = -1;
		clear_bit(In_sync, &rdev->flags);
		clear_bit(Bitmap_sync, &rdev->flags);
		err = rdev->mddev->pers->
			hot_add_disk(rdev->mddev, rdev);
		if (err) {
			rdev->raid_disk = -1;
			return err;
		} else
			sysfs_notify_dirent_safe(rdev->sysfs_state);
		if (sysfs_link_rdev(rdev->mddev, rdev))
			/* failure here is OK */;
		/* don't wakeup anyone, leave that to userspace. */
	} else {
		if (slot >= rdev->mddev->raid_disks &&
		    slot >= rdev->mddev->raid_disks + rdev->mddev->delta_disks)
			return -ENOSPC;
		rdev->raid_disk = slot;
		/* assume it is working */
		clear_bit(Faulty, &rdev->flags);
		clear_bit(WriteMostly, &rdev->flags);
		set_bit(In_sync, &rdev->flags);
		sysfs_notify_dirent_safe(rdev->sysfs_state);
	}
	return len;
}

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