From c13555c63ad5dfdf9b4f81c8a2e6632d9de05fa3 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@redhat.com>
Date: Fri, 27 Jul 2012 15:08:04 +0100
Subject: [PATCH] --- yaml --- r: 319471 b: refs/heads/master c:
 a58a935d5a1b2ad267017a68c3a1bca26226cc76 h: refs/heads/master i:   319469:
 d38e196ebb17ae0e67872e4584a3a2fcf0b705dd   319467:
 d9cfe67e27aade3fd7baf18512fc36990bd65342   319463:
 1b6c0e024d23bb3ffa3cd8547535791919866adb   319455:
 3c1b36bee0774baefb0398bbc764f4c225318b13 v: v3

---
 [refs]                      |  2 +-
 trunk/drivers/md/dm-mpath.c | 47 ++++++++++++++++++++++++++++++++-----
 2 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/[refs] b/[refs]
index 722f39f42ce1..d6b30a034d1e 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: f9a8e0cd261fc05820539b0ea613686a32795406
+refs/heads/master: a58a935d5a1b2ad267017a68c3a1bca26226cc76
diff --git a/trunk/drivers/md/dm-mpath.c b/trunk/drivers/md/dm-mpath.c
index 638dae048b4f..8a3b2d53f81b 100644
--- a/trunk/drivers/md/dm-mpath.c
+++ b/trunk/drivers/md/dm-mpath.c
@@ -85,6 +85,7 @@ struct multipath {
 	unsigned queue_io:1;		/* Must we queue all I/O? */
 	unsigned queue_if_no_path:1;	/* Queue I/O if last path fails? */
 	unsigned saved_queue_if_no_path:1; /* Saved state during suspension */
+	unsigned retain_attached_hw_handler:1; /* If there's already a hw_handler present, don't change it. */
 
 	unsigned pg_init_retries;	/* Number of times to retry pg_init */
 	unsigned pg_init_count;		/* Number of times pg_init called */
@@ -568,6 +569,8 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 	int r;
 	struct pgpath *p;
 	struct multipath *m = ti->private;
+	struct request_queue *q = NULL;
+	const char *attached_handler_name;
 
 	/* we need at least a path arg */
 	if (as->argc < 1) {
@@ -586,13 +589,37 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 		goto bad;
 	}
 
-	if (m->hw_handler_name) {
-		struct request_queue *q = bdev_get_queue(p->path.dev->bdev);
+	if (m->retain_attached_hw_handler || m->hw_handler_name)
+		q = bdev_get_queue(p->path.dev->bdev);
+
+	if (m->retain_attached_hw_handler) {
+		attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
+		if (attached_handler_name) {
+			/*
+			 * Reset hw_handler_name to match the attached handler
+			 * and clear any hw_handler_params associated with the
+			 * ignored handler.
+			 *
+			 * NB. This modifies the table line to show the actual
+			 * handler instead of the original table passed in.
+			 */
+			kfree(m->hw_handler_name);
+			m->hw_handler_name = attached_handler_name;
+
+			kfree(m->hw_handler_params);
+			m->hw_handler_params = NULL;
+		}
+	}
 
+	if (m->hw_handler_name) {
+		/*
+		 * Increments scsi_dh reference, even when using an
+		 * already-attached handler.
+		 */
 		r = scsi_dh_attach(q, m->hw_handler_name);
 		if (r == -EBUSY) {
 			/*
-			 * Already attached to different hw_handler,
+			 * Already attached to different hw_handler:
 			 * try to reattach with correct one.
 			 */
 			scsi_dh_detach(q);
@@ -760,7 +787,7 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
 	const char *arg_name;
 
 	static struct dm_arg _args[] = {
-		{0, 5, "invalid number of feature args"},
+		{0, 6, "invalid number of feature args"},
 		{1, 50, "pg_init_retries must be between 1 and 50"},
 		{0, 60000, "pg_init_delay_msecs must be between 0 and 60000"},
 	};
@@ -781,6 +808,11 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
 			continue;
 		}
 
+		if (!strcasecmp(arg_name, "retain_attached_hw_handler")) {
+			m->retain_attached_hw_handler = 1;
+			continue;
+		}
+
 		if (!strcasecmp(arg_name, "pg_init_retries") &&
 		    (argc >= 1)) {
 			r = dm_read_arg(_args + 1, as, &m->pg_init_retries, &ti->error);
@@ -1364,13 +1396,16 @@ static int multipath_status(struct dm_target *ti, status_type_t type,
 	else {
 		DMEMIT("%u ", m->queue_if_no_path +
 			      (m->pg_init_retries > 0) * 2 +
-			      (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2);
+			      (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2 +
+			      m->retain_attached_hw_handler);
 		if (m->queue_if_no_path)
 			DMEMIT("queue_if_no_path ");
 		if (m->pg_init_retries)
 			DMEMIT("pg_init_retries %u ", m->pg_init_retries);
 		if (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT)
 			DMEMIT("pg_init_delay_msecs %u ", m->pg_init_delay_msecs);
+		if (m->retain_attached_hw_handler)
+			DMEMIT("retain_attached_hw_handler ");
 	}
 
 	if (!m->hw_handler_name || type == STATUSTYPE_INFO)
@@ -1656,7 +1691,7 @@ static int multipath_busy(struct dm_target *ti)
  *---------------------------------------------------------------*/
 static struct target_type multipath_target = {
 	.name = "multipath",
-	.version = {1, 4, 0},
+	.version = {1, 5, 0},
 	.module = THIS_MODULE,
 	.ctr = multipath_ctr,
 	.dtr = multipath_dtr,