1 files changed, 41 insertions, 6 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 638dae048b4f..8a3b2d53f81b 100644
--- a/drivers/md/dm-mpath.c
+++ b/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 @@ out:
  *---------------------------------------------------------------*/
 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,