[Cluster-devel] [PATCH] qdiskd: restrict master_wins to 2 node cluster

[Fabio M. Di Nitto <fdinitto@redhat.com>]

From: "Fabio M. Di Nitto" <fdinitto@redhat.com>

given enough mingling of cluster.conf it was possible to
break quorum rule #1: there is only one quorum in a cluster at
any given time.

this change restricts master_wins to 2 node cluster only
and provides extra feedback to the user (via logging) on why
the mode is disabled.

Resolves: rhbz#838047

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>
---
 cman/man/qdisk.5  |    5 +++--
 cman/qdisk/disk.h |    1 +
 cman/qdisk/main.c |   22 +++++++++++++++-------
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/cman/man/qdisk.5 b/cman/man/qdisk.5
index ca974fa..938ed69 100644
--- a/cman/man/qdisk.5
+++ b/cman/man/qdisk.5
@@ -297,8 +297,9 @@ and qdiskd's timeout (interval*tko) should be less than half of
 Totem's token timeout.  See section 3.3.1 for more information.
 
 This option only takes effect if there are no heuristics
-configured.  Usage of this option in configurations with more than
-two cluster nodes is undefined and should not be done.
+configured and it is valid only for 2 node cluster.
+This option is automatically disabled if heuristics are
+defined or cluster has more than 2 nodes configured.
 
 In a two-node cluster with no heuristics and no defined vote
 count (see above), this mode is turned by default.  If enabled in
diff --git a/cman/qdisk/disk.h b/cman/qdisk/disk.h
index fd80fa6..1792377 100644
--- a/cman/qdisk/disk.h
+++ b/cman/qdisk/disk.h
@@ -249,6 +249,7 @@ typedef struct {
 	int qc_master;		/* Master?! */
 	int qc_config;
 	int qc_token_timeout;
+	int qc_auto_votes;
 	disk_node_state_t qc_disk_status;
 	disk_node_state_t qc_status;
 	run_flag_t qc_flags;
diff --git a/cman/qdisk/main.c b/cman/qdisk/main.c
index 32677a2..e14d534 100644
--- a/cman/qdisk/main.c
+++ b/cman/qdisk/main.c
@@ -1444,7 +1444,7 @@ auto_qdisk_votes(int desc)
 		logt_print(LOG_ERR, "Unable to determine qdiskd votes "
 			   "automatically\n");
 	else
-		logt_print(LOG_DEBUG, "Setting votes to %d\n", ret);
+		logt_print(LOG_DEBUG, "Setting autocalculated votes to %d\n", ret);
  
  	return (ret);
 }
@@ -1606,6 +1606,8 @@ get_dynamic_config_data(qd_ctx *ctx, int ccsfd)
 		ctx->qc_flags &= ~RF_AUTO_VOTES;
 	}
 
+	ctx->qc_auto_votes = auto_qdisk_votes(ccsfd);
+
 	snprintf(query, sizeof(query), "/cluster/quorumd/@votes");
 	if (ccs_get(ccsfd, query, &val) == 0) {
 		ctx->qc_votes = atoi(val);
@@ -1613,7 +1615,7 @@ get_dynamic_config_data(qd_ctx *ctx, int ccsfd)
 		if (ctx->qc_votes < 0)
 			ctx->qc_votes = 0;
 	} else {
-		ctx->qc_votes = auto_qdisk_votes(ccsfd);
+		ctx->qc_votes = ctx->qc_auto_votes;
 		if (ctx->qc_votes < 0) {
 			if (ctx->qc_config) {
 				logt_print(LOG_WARNING, "Unable to determine "
@@ -1879,15 +1881,21 @@ get_config_data(qd_ctx *ctx, struct h_data *h, int maxh, int *cfh)
 	*cfh = configure_heuristics(ccsfd, h, maxh,
 				    ctx->qc_interval * (ctx->qc_tko - 1));
 
-	if (*cfh) {
-		if (ctx->qc_flags & RF_MASTER_WINS) {
-			logt_print(LOG_WARNING, "Master-wins mode disabled\n");
+	if (ctx->qc_flags & RF_MASTER_WINS) {
+		if (*cfh) {
+			logt_print(LOG_WARNING, "Master-wins mode disabled "
+						"(not compatible with heuristics)\n");
+			ctx->qc_flags &= ~RF_MASTER_WINS;
+		}
+		if (ctx->qc_auto_votes != 1) {
+			logt_print(LOG_WARNING, "Master-wins mode disabled "
+						"(not compatible with more than 2 nodes)\n");
 			ctx->qc_flags &= ~RF_MASTER_WINS;
 		}
 	} else {
 		if (ctx->qc_flags & RF_AUTO_VOTES &&
-		    !(ctx->qc_flags & RF_MASTER_WINS) &&
-		    ctx->qc_votes == 1) { 
+		    !*cfh &&
+		    ctx->qc_auto_votes == 1) { 
 			/* Two node cluster, no heuristics, 1 vote for
 			 * quorum disk daemon.  Safe to enable master-wins.
 			 * In fact, qdiskd without master-wins in this config
-- 
1.7.7.6