chunk_size_store(struct mddev *mddev, const char *buf, size_t len)
{
	unsigned long n;
	int err;

	err = kstrtoul(buf, 10, &n);
	if (err < 0)
		return err;

	err = mddev_lock(mddev);
	if (err)
		return err;
	if (mddev->pers) {
		if (mddev->pers->check_reshape == NULL)
			err = -EBUSY;
		else if (mddev->ro)
			err = -EROFS;
		else {
			mddev->new_chunk_sectors = n >> 9;
			err = mddev->pers->check_reshape(mddev);
			if (err)
				mddev->new_chunk_sectors = mddev->chunk_sectors;
		}
	} else {
		mddev->new_chunk_sectors = n >> 9;
		if (mddev->reshape_position == MaxSector)
			mddev->chunk_sectors = n >> 9;
	}
	mddev_unlock(mddev);
	return err ?: len;
}

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