[XFS] Fix up the calculation of the reservation overhead to hopefully

	 *

	 * The following lines of code account for non-transaction data

	 * which occupy space in the on-disk log.

	 */

	 *

	 * Normal form of a transaction is:

	 * <oph><trans-hdr><start-oph><reg1-oph><reg1><reg2-oph>...<commit-oph>

	 * and then there are LR hdrs, split-recs and roundoff at end of syncs.

	 *

	 * We need to account for all the leadup data and trailer data

	 * around the transaction data.

	 * And then we need to account for the worst case in terms of using

	 * more space.

	 * The worst case will happen if:

	 * - the placement of the transaction happens to be such that the

	 *   roundoff is at its maximum

	 * - the transaction data is synced before the commit record is synced

	 *   i.e. <transaction-data><roundoff> | <commit-rec><roundoff>

	 *   Therefore the commit record is in its own Log Record.

	 *   This can happen as the commit record is called with its

	 *   own region to xlog_write().

	 *   This then means that in the worst case, roundoff can happen for

	 *   the commit-rec as well.

	 *   The commit-rec is smaller than padding in this scenario and so it is

	 *   not added separately.

	 */

	/* for trans header */

	unit_bytes += sizeof(xlog_op_header_t);

	unit_bytes += sizeof(xfs_trans_header_t);

	/* for start-rec */

	unit_bytes += sizeof(xlog_op_header_t);

	/* for padding */

	/* for LR headers */

	num_headers = ((unit_bytes + log->l_iclog_size-1) >> log->l_iclog_size_log);

	unit_bytes += log->l_iclog_hsize * num_headers;

	/* for commit-rec LR header - note: padding will subsume the ophdr */

	unit_bytes += log->l_iclog_hsize;

	/* for split-recs - ophdrs added when data split over LRs */

	unit_bytes += sizeof(xlog_op_header_t) * num_headers;

	/* for roundoff padding for transaction data and one for commit record */

	if (XFS_SB_VERSION_HASLOGV2(&log->l_mp->m_sb) &&

	    log->l_mp->m_sb.sb_logsunit > 1) {

		/* log su roundoff */

		unit_bytes += log->l_mp->m_sb.sb_logsunit;  

		unit_bytes += 2*log->l_mp->m_sb.sb_logsunit;

	} else {

		/* BB roundoff */

		unit_bytes += BBSIZE;

		unit_bytes += 2*BBSIZE;

        }

	/* for commit-rec */

	unit_bytes += sizeof(xlog_op_header_t);

	/* for LR headers */

	num_headers = ((unit_bytes + log->l_iclog_size-1) >> log->l_iclog_size_log);

	unit_bytes += log->l_iclog_hsize * num_headers;

	tic->t_unit_res		= unit_bytes;

	tic->t_curr_res		= unit_bytes;

	tic->t_cnt		= cnt;