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[dm-devel] [PATCH] multipath: add followover failback mode



This patch adds a new failback mode, followover, to deal with multiple
computers accessing the same active/passive storage devices.  In these
cases, if only one node loses access to the primary paths, it will
force a trespass to the secondary paths.  If the nodes are configured
with immediate failback, the other nodes with trespass back to the
primary paths, and the machines will ping-pong the storage. If the
nodes are configured with manual failback, this won't happen. However
when the primary path is restored on the node that lost access to it,
the nodes won't automatically failback to it.  In followover mode, they
will.

Followover mode works by only failing back when a path comes back online
from a pathgroup that previously had no working paths.  For this to
work, the paths need an additional attribute, chkrstate. This is just like
the path state, except it is not updated when the paths state is changed
by the kernel, only when the path checker function sees that the path is
down.  This is necessary because when a trespass occurs, all the outstanding
IO to the previously active paths will fail, and the kernel will mark the
path as down.  But for failback to happen in followover mode, the paths must
actually be down, not just in a ghost state.

Signed-off-by: Benjamin Marzinski <bmarzins redhat com>
---
 libmultipath/dict.c        |   12 ++++++++++++
 libmultipath/discovery.c   |    6 +++---
 libmultipath/print.c       |    2 ++
 libmultipath/structs.h     |    4 +++-
 multipath/main.c           |    2 +-
 multipath/multipath.conf.5 |    5 +++++
 multipathd/main.c          |   35 ++++++++++++++++++++++++++++++++++-
 7 files changed, 60 insertions(+), 6 deletions(-)

Index: multipath-tools-120518/libmultipath/dict.c
===================================================================
--- multipath-tools-120518.orig/libmultipath/dict.c
+++ multipath-tools-120518/libmultipath/dict.c
@@ -398,6 +398,8 @@ default_failback_handler(vector strvec)
 		conf->pgfailback = -FAILBACK_MANUAL;
 	else if (strlen(buff) == 9 && !strcmp(buff, "immediate"))
 		conf->pgfailback = -FAILBACK_IMMEDIATE;
+	else if (strlen(buff) == 10 && !strcmp(buff, "followover"))
+		conf->pgfailback = -FAILBACK_FOLLOWOVER;
 	else
 		conf->pgfailback = atoi(buff);
 
@@ -1053,6 +1055,8 @@ hw_failback_handler(vector strvec)
 		hwe->pgfailback = -FAILBACK_MANUAL;
 	else if (strlen(buff) == 9 && !strcmp(buff, "immediate"))
 		hwe->pgfailback = -FAILBACK_IMMEDIATE;
+	else if (strlen(buff) == 10 && !strcmp(buff, "followover"))
+		hwe->pgfailback = -FAILBACK_FOLLOWOVER;
 	else
 		hwe->pgfailback = atoi(buff);
 
@@ -1351,6 +1355,8 @@ mp_failback_handler(vector strvec)
 		mpe->pgfailback = -FAILBACK_MANUAL;
 	else if (strlen(buff) == 9 && !strcmp(buff, "immediate"))
 		mpe->pgfailback = -FAILBACK_IMMEDIATE;
+	else if (strlen(buff) == 10 && !strcmp(buff, "followover"))
+		mpe->pgfailback = -FAILBACK_FOLLOWOVER;
 	else
 		mpe->pgfailback = atoi(buff);
 
@@ -1769,6 +1775,8 @@ snprint_mp_failback (char * buff, int le
 		return snprintf(buff, len, "manual");
 	case -FAILBACK_IMMEDIATE:
 		return snprintf(buff, len, "immediate");
+	case -FAILBACK_FOLLOWOVER:
+		return snprintf(buff, len, "followover");
 	default:
 		return snprintf(buff, len, "%i", mpe->pgfailback);
 	}
@@ -2130,6 +2138,8 @@ snprint_hw_failback (char * buff, int le
 		return snprintf(buff, len, "manual");
 	case -FAILBACK_IMMEDIATE:
 		return snprintf(buff, len, "immediate");
+	case -FAILBACK_FOLLOWOVER:
+		return snprintf(buff, len, "followover");
 	default:
 		return snprintf(buff, len, "%i", hwe->pgfailback);
 	}
@@ -2394,6 +2404,8 @@ snprint_def_failback (char * buff, int l
 		return snprintf(buff, len, "manual");
 	case -FAILBACK_IMMEDIATE:
 		return snprintf(buff, len, "immediate");
+	case -FAILBACK_FOLLOWOVER:
+		return snprintf(buff, len, "followover");
 	default:
 		return snprintf(buff, len, "%i", conf->pgfailback);
 	}
Index: multipath-tools-120518/libmultipath/print.c
===================================================================
--- multipath-tools-120518.orig/libmultipath/print.c
+++ multipath-tools-120518/libmultipath/print.c
@@ -143,6 +143,8 @@ snprint_failback (char * buff, size_t le
 {
 	if (mpp->pgfailback == -FAILBACK_IMMEDIATE)
 		return snprintf(buff, len, "immediate");
+	if (mpp->pgfailback == -FAILBACK_FOLLOWOVER)
+		return snprintf(buff, len, "followover");
 
 	if (!mpp->failback_tick)
 		return snprintf(buff, len, "-");
Index: multipath-tools-120518/libmultipath/structs.h
===================================================================
--- multipath-tools-120518.orig/libmultipath/structs.h
+++ multipath-tools-120518/libmultipath/structs.h
@@ -39,7 +39,8 @@ enum rr_weight_mode {
 enum failback_mode {
 	FAILBACK_UNDEF,
 	FAILBACK_MANUAL,
-	FAILBACK_IMMEDIATE
+	FAILBACK_IMMEDIATE,
+	FAILBACK_FOLLOWOVER
 };
 
 enum sysfs_buses {
@@ -151,6 +152,7 @@ struct path {
 	int offline;
 	int state;
 	int dmstate;
+	int chkrstate;
 	int failcount;
 	int priority;
 	int pgindex;
Index: multipath-tools-120518/multipathd/main.c
===================================================================
--- multipath-tools-120518.orig/multipathd/main.c
+++ multipath-tools-120518/multipathd/main.c
@@ -995,6 +995,32 @@ mpvec_garbage_collector (struct vectors
 	}
 }
 
+/* This is called after a path has started working again. It the multipath
+ * device for this path uses the followover failback type, and this is the
+ * best pathgroup, and this is the first path in the pathgroup to come back
+ * up, then switch to this pathgroup */
+static int
+followover_should_failback(struct path * pp)
+{
+	struct pathgroup * pgp;
+	struct path *pp1;
+	int i;
+
+	if (pp->mpp->pgfailback != -FAILBACK_FOLLOWOVER ||
+	    !pp->mpp->pg || !pp->pgindex ||
+	    pp->pgindex != pp->mpp->bestpg)
+		return 0;
+
+	pgp = VECTOR_SLOT(pp->mpp->pg, pp->pgindex - 1);
+	vector_foreach_slot(pgp->paths, pp1, i) {
+		if (pp1 == pp)
+			continue;
+		if (pp1->chkrstate != PATH_DOWN && pp1->chkrstate != PATH_SHAKY)
+			return 0;
+	}
+	return 1;
+}
+
 static void
 defered_failback_tick (vector mpvec)
 {
@@ -1092,6 +1118,8 @@ check_path (struct vectors * vecs, struc
 {
 	int newstate;
 	int new_path_up = 0;
+	int chkr_new_path_up = 0;
+	int oldchkrstate = pp->chkrstate;
 
 	if (!pp->mpp)
 		return;
@@ -1130,6 +1158,7 @@ check_path (struct vectors * vecs, struc
 			pp->dev);
 		pp->dmstate = PSTATE_UNDEF;
 	}
+	pp->chkrstate = newstate;
 	if (newstate != pp->state) {
 		int oldstate = pp->state;
 		pp->state = newstate;
@@ -1182,6 +1211,9 @@ check_path (struct vectors * vecs, struc
 
 		new_path_up = 1;
 
+		if (oldchkrstate != PATH_UP && oldchkrstate != PATH_GHOST)
+			chkr_new_path_up = 1;
+
 		/*
 		 * if at least one path is up in a group, and
 		 * the group is disabled, re-enable it
@@ -1233,7 +1265,8 @@ check_path (struct vectors * vecs, struc
 		    (new_path_up || pp->mpp->failback_tick <= 0))
 			pp->mpp->failback_tick =
 				pp->mpp->pgfailback + 1;
-		else if (pp->mpp->pgfailback == -FAILBACK_IMMEDIATE)
+		else if (pp->mpp->pgfailback == -FAILBACK_IMMEDIATE ||
+			 (chkr_new_path_up && followover_should_failback(pp)))
 			switch_pathgroup(pp->mpp);
 	}
 }
Index: multipath-tools-120518/multipath/multipath.conf.5
===================================================================
--- multipath-tools-120518.orig/multipath/multipath.conf.5
+++ multipath-tools-120518/multipath/multipath.conf.5
@@ -254,6 +254,11 @@ active paths.
 .B manual
 Do not perform automatic failback.
 .TP
+.B followover
+Only perform automatic failback when the first path of a pathgroup
+becomes active. This keeps a node from automatically failing back when
+another node requested the failover.
+.TP
 .B values > 0
 deferred failback (time to defer in seconds)
 .TP
Index: multipath-tools-120518/libmultipath/discovery.c
===================================================================
--- multipath-tools-120518.orig/libmultipath/discovery.c
+++ multipath-tools-120518/libmultipath/discovery.c
@@ -878,13 +878,13 @@ pathinfo (struct path *pp, vector hwtabl
 
 	if (mask & DI_CHECKER) {
 		if (path_state == PATH_UP) {
-			pp->state = get_state(pp, 0);
+			pp->chkrstate = pp->state = get_state(pp, 0);
 			if (pp->state == PATH_UNCHECKED ||
 			    pp->state == PATH_WILD)
 				goto blank;
 		} else {
 			condlog(3, "%s: path inaccessible", pp->dev);
-			pp->state = path_state;
+			pp->chkrstate = pp->state = path_state;
 		}
 	}
 
@@ -912,7 +912,7 @@ blank:
 	 * Recoverable error, for example faulty or offline path
 	 */
 	memset(pp->wwid, 0, WWID_SIZE);
-	pp->state = PATH_DOWN;
+	pp->chkrstate = pp->state = PATH_DOWN;
 
 	return 0;
 }
Index: multipath-tools-120518/multipath/main.c
===================================================================
--- multipath-tools-120518.orig/multipath/main.c
+++ multipath-tools-120518/multipath/main.c
@@ -144,7 +144,7 @@ update_paths (struct multipath * mpp)
 					/*
 					 * path is not in sysfs anymore
 					 */
-					pp->state = PATH_DOWN;
+					pp->chkrstate = pp->state = PATH_DOWN;
 					continue;
 				}
 				pp->mpp = mpp;


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