[SCSI] scsi_dh: attach to hardware handler from dm-mpath

multipath keeps a separate device table which may be
more current than the built-in one.
So we should make sure to always call ->attach whenever
a multipath map with hardware handler is instantiated.
And we should call ->detach on removal, too.

[sekharan: update as per comments from agk]
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

3 files changed, 87 insertions, 0 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index fea966d66f98..71dd65aa31b6 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -147,9 +147,12 @@ static struct priority_group *alloc_priority_group(void)
 static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
 {
         struct pgpath *pgpath, *tmp;
+        struct multipath *m = ti->private;
 
         list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
                 list_del(&pgpath->list);
+                if (m->hw_handler_name)
+                        scsi_dh_detach(bdev_get_queue(pgpath->path.dev->bdev));
                 dm_put_device(ti, pgpath->path.dev);
                 free_pgpath(pgpath);
         }
@@ -548,6 +551,7 @@ static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
 {
         int r;
         struct pgpath *p;
+        struct multipath *m = ti->private;
 
         /* we need at least a path arg */
         if (as->argc < 1) {
@@ -566,6 +570,15 @@ static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
                 goto bad;
         }
 
+        if (m->hw_handler_name) {
+                r = scsi_dh_attach(bdev_get_queue(p->path.dev->bdev),
+                                   m->hw_handler_name);
+                if (r < 0) {
+                        dm_put_device(ti, p->path.dev);
+                        goto bad;
+                }
+        }
+
         r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
         if (r) {
                 dm_put_device(ti, p->path.dev);
diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
index e90df9dd3e65..a9159681ff27 100644
--- a/drivers/scsi/device_handler/scsi_dh.c
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -369,6 +369,70 @@ int scsi_dh_handler_exist(const char *name)
 }
 EXPORT_SYMBOL_GPL(scsi_dh_handler_exist);
 
+/*
+ * scsi_dh_handler_attach - Attach device handler
+ * @sdev - sdev the handler should be attached to
+ * @name - name of the handler to attach
+ */
+int scsi_dh_attach(struct request_queue *q, const char *name)
+{
+        unsigned long flags;
+        struct scsi_device *sdev;
+        struct scsi_device_handler *scsi_dh;
+        int err = 0;
+
+        scsi_dh = get_device_handler(name);
+        if (!scsi_dh)
+                return -EINVAL;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        sdev = q->queuedata;
+        if (!sdev || !get_device(&sdev->sdev_gendev))
+                err = -ENODEV;
+        spin_unlock_irqrestore(q->queue_lock, flags);
+
+        if (!err) {
+                err = scsi_dh_handler_attach(sdev, scsi_dh);
+
+                put_device(&sdev->sdev_gendev);
+        }
+        return err;
+}
+EXPORT_SYMBOL_GPL(scsi_dh_attach);
+
+/*
+ * scsi_dh_handler_detach - Detach device handler
+ * @sdev - sdev the handler should be detached from
+ *
+ * This function will detach the device handler only
+ * if the sdev is not part of the internal list, ie
+ * if it has been attached manually.
+ */
+void scsi_dh_detach(struct request_queue *q)
+{
+        unsigned long flags;
+        struct scsi_device *sdev;
+        struct scsi_device_handler *scsi_dh = NULL;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        sdev = q->queuedata;
+        if (!sdev || !get_device(&sdev->sdev_gendev))
+                sdev = NULL;
+        spin_unlock_irqrestore(q->queue_lock, flags);
+
+        if (!sdev)
+                return;
+
+        if (sdev->scsi_dh_data) {
+                /* if sdev is not on internal list, detach */
+                scsi_dh = sdev->scsi_dh_data->scsi_dh;
+                if (!device_handler_match(scsi_dh, sdev))
+                        scsi_dh_handler_detach(sdev, scsi_dh);
+        }
+        put_device(&sdev->sdev_gendev);
+}
+EXPORT_SYMBOL_GPL(scsi_dh_detach);
+
 static struct notifier_block scsi_dh_nb = {
         .notifier_call = scsi_dh_notifier
 };
diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
index e15e2aade69c..33efce20c26c 100644
--- a/include/scsi/scsi_dh.h
+++ b/include/scsi/scsi_dh.h
@@ -58,6 +58,8 @@ enum {
 #if defined(CONFIG_SCSI_DH) || defined(CONFIG_SCSI_DH_MODULE)
 extern int scsi_dh_activate(struct request_queue *);
 extern int scsi_dh_handler_exist(const char *);
+extern int scsi_dh_attach(struct request_queue *, const char *);
+extern void scsi_dh_detach(struct request_queue *);
 #else
 static inline int scsi_dh_activate(struct request_queue *req)
 {
@@ -67,4 +69,12 @@ static inline int scsi_dh_handler_exist(const char *name)
 {
         return 0;
 }
+static inline int scsi_dh_attach(struct request_queue *req, const char *name)
+{
+        return SCSI_DH_NOSYS;
+}
+static inline void scsi_dh_detach(struct request_queue *q)
+{
+        return;
+}
 #endif