xfs: embed the xlog_op_header in the commit record

Remove the final case where xlog_write() has to prepend an opheader
to a log transaction. Similar to the start record, the commit record
is just an empty opheader with a XLOG_COMMIT_TRANS type, so we can
just make this the payload for the region being passed to
xlog_write() and remove the special handling in xlog_write() for
the commit record.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_log.c

@@ -2267,11 +2267,10 @@ xlog_write_calc_vec_length(
 
 	/* Don't account for regions with embedded ophdrs */
 	if (optype && headers > 0) {
-		if (optype & XLOG_UNMOUNT_TRANS)
-			headers--;
+		headers--;
 		if (optype & XLOG_START_TRANS) {
-			ASSERT(headers >= 2);
-			headers -= 2;
+			ASSERT(headers >= 1);
+			headers--;
 		}
 	}
 
@@ -2472,14 +2471,6 @@ xlog_write(
 	int			data_cnt = 0;
 	int			error = 0;
 
-	/*
-	 * If this is a commit or unmount transaction, we don't need a start
-	 * record to be written.  We do, however, have to account for the commit
-	 * header that gets written. Hence we always have to account for an
-	 * extra xlog_op_header here for commit records.
-	 */
-	if (optype & XLOG_COMMIT_TRANS)
-		ticket->t_curr_res -= sizeof(struct xlog_op_header);
 	if (ticket->t_curr_res < 0) {
 		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
 		     "ctx ticket reservation ran out. Need to up reservation");
@@ -2536,14 +2527,13 @@ xlog_write(
 			/*
 			 * The XLOG_START_TRANS has embedded ophdrs for the
 			 * start record and transaction header. They will always
-			 * be the first two regions in the lv chain.
+			 * be the first two regions in the lv chain. Commit and
+			 * unmount records also have embedded ophdrs.
 			 */
-			if (optype & XLOG_START_TRANS) {
+			if (optype) {
 				ophdr = reg->i_addr;
 				if (index)
 					optype &= ~XLOG_START_TRANS;
-			} else if (optype & XLOG_UNMOUNT_TRANS) {
-				ophdr = reg->i_addr;
 			} else {
 				ophdr = xlog_write_setup_ophdr(log, ptr,
 							ticket, optype);

fs/xfs/xfs_log_cil.c

@@ -844,9 +844,14 @@ xlog_cil_write_commit_record(
 	struct xfs_cil_ctx	*ctx)
 {
 	struct xlog		*log = ctx->cil->xc_log;
+	struct xlog_op_header	ophdr = {
+		.oh_clientid = XFS_TRANSACTION,
+		.oh_tid = cpu_to_be32(ctx->ticket->t_tid),
+		.oh_flags = XLOG_COMMIT_TRANS,
+	};
 	struct xfs_log_iovec	reg = {
-		.i_addr = NULL,
-		.i_len = 0,
+		.i_addr = &ophdr,
+		.i_len = sizeof(struct xlog_op_header),
 		.i_type = XLOG_REG_TYPE_COMMIT,
 	};
 	struct xfs_log_vec	vec = {
@@ -862,6 +867,8 @@ xlog_cil_write_commit_record(
 	if (error)
 		return error;
 
+	/* account for space used by record data */
+	ctx->ticket->t_curr_res -= reg.i_len;
 	error = xlog_write(log, ctx, &vec, ctx->ticket, XLOG_COMMIT_TRANS);
 	if (error)
 		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);