xfs: ensure correct log item buffer alignment

		/*

		 * We 64-bit align the length of each iovec so that the start

		 * of the next one is naturally aligned.  We'll need to

		 * account for that slack space here.

		 * account for that slack space here. Then round nbytes up

		 * to 64-bit alignment so that the initial buffer alignment is

		 * easy to calculate and verify.

		 */

		nbytes += niovecs * sizeof(uint64_t);

		nbytes = round_up(nbytes, sizeof(uint64_t));

		/* grab the old item if it exists for reservation accounting */

		old_lv = lip->li_lv;

		/* calc buffer size */

		buf_size = sizeof(struct xfs_log_vec) + nbytes +

				niovecs * sizeof(struct xfs_log_iovec);

		/*

		 * The data buffer needs to start 64-bit aligned, so round up

		 * that space to ensure we can align it appropriately and not

		 * overrun the buffer.

		 */

		buf_size = nbytes +

			   round_up((sizeof(struct xfs_log_vec) +

				     niovecs * sizeof(struct xfs_log_iovec)),

				    sizeof(uint64_t));

		/* compare to existing item size */

		if (lip->li_lv && buf_size <= lip->li_lv->lv_size) {

		/* The allocated data region lies beyond the iovec region */

		lv->lv_buf_len = 0;

		lv->lv_buf = (char *)lv + buf_size - nbytes;

		ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));

		lip->li_ops->iop_format(lip, lv);

insert:

		ASSERT(lv->lv_buf_len <= nbytes);