Chandra, I have one comment on this patch..
> static inline int scsi_dh_handler_exist(const char *name)
> Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh.c
> +++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh.c
> @@ -214,7 +214,7 @@ store_dh_state(struct device *dev, struc
> * Activate a device handler
> */
> if (scsi_dh->activate)
> - err = scsi_dh->activate(sdev);
> + err = scsi_dh->activate(sdev, NULL, NULL);
This might cause problems in handlers. We don’t do NULL check in attach routine.
> else
> err = 0;
> }
> @@ -411,10 +411,17 @@ EXPORT_SYMBOL_GPL(scsi_unregister_device
> /*
> * scsi_dh_activate - activate the path associated with the
> scsi_device
> * corresponding to the given request queue.
> - * @q - Request queue that is associated with the scsi_device to be
> - * activated.
> + * Returns immediately without waiting for activation to be
> completed.
> + * @q - Request queue that is associated with the scsi_device to be
> + * activated.
> + * @fn - Function to be called upon completion of the activation.
> + * Function fn is called with data (below) and the error code.
> + * Function fn may be called from the same calling context.
> So,
> + * do not hold the lock in the caller which may be needed in
> fn.
> + * @data - data passed to the function fn upon completion.
> + *
> */
> -int scsi_dh_activate(struct request_queue *q)
> +int scsi_dh_activate(struct request_queue *q, activate_complete fn,
> void *data)
> {
> int err = 0;
> unsigned long flags;
> @@ -433,7 +440,7 @@ int scsi_dh_activate(struct request_queu
> return err;
>
> if (scsi_dh->activate)
> - err = scsi_dh->activate(sdev);
> + err = scsi_dh->activate(sdev, fn, data);
> put_device(&sdev->sdev_gendev);
> return err;
> }
> Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh_rdac.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh_rdac.c
> +++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh_rdac.c
> @@ -516,7 +516,7 @@ done:
> return err;
> }
>
> -static int rdac_activate(struct scsi_device *sdev)
> +static int rdac_activate(struct scsi_device *sdev, activate_complete
> fn, void *data)
> {
> struct rdac_dh_data *h = get_rdac_data(sdev);
> int err = SCSI_DH_OK;
> @@ -539,7 +539,9 @@ static int rdac_activate(struct scsi_dev
> if (h->lun_state == RDAC_LUN_UNOWNED)
> err = send_mode_select(sdev, h);
> done:
> - return err;
> + if (fn)
> + fn(data, err);
> + return 0;
> }
>
> static int rdac_prep_fn(struct scsi_device *sdev, struct request *req)
> Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh_alua.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -652,7 +652,7 @@ out:
> * based on a certain policy. But until we actually encounter them it
> * should be okay.
> */
> -static int alua_activate(struct scsi_device *sdev)
> +static int alua_activate(struct scsi_device *sdev, activate_complete
> fn, void *data)
> {
> struct alua_dh_data *h = get_alua_data(sdev);
> int err = SCSI_DH_OK;
> @@ -667,7 +667,9 @@ static int alua_activate(struct scsi_dev
> err = alua_stpg(sdev, TPGS_STATE_OPTIMIZED, h);
>
> out:
> - return err;
> + if (fn)
> + fn(data, err);
> + return 0;
> }
>
> /*
> Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh_emc.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh_emc.c
> +++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh_emc.c
> @@ -528,7 +528,7 @@ retry:
> return err;
> }
>
> -static int clariion_activate(struct scsi_device *sdev)
> +static int clariion_activate(struct scsi_device *sdev,
> activate_complete fn, void *data)
> {
> struct clariion_dh_data *csdev = get_clariion_data(sdev);
> int result;
> @@ -559,7 +559,9 @@ done:
> csdev->port, lun_state[csdev->lun_state],
> csdev->default_sp + 'A');
>
> - return result;
> + if (fn)
> + fn(data, result);
> + return 0;
> }
>
> static const struct scsi_dh_devlist clariion_dev_list[] = {
> Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> +++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> @@ -268,7 +268,7 @@ static int hp_sw_prep_fn(struct scsi_dev
> * activate the passive path (and deactivate the
> * previously active one).
> */
> -static int hp_sw_activate(struct scsi_device *sdev)
> +static int hp_sw_activate(struct scsi_device *sdev, activate_complete
> fn, void *data)
> {
> int ret = SCSI_DH_OK;
> struct hp_sw_dh_data *h = get_hp_sw_data(sdev);
> @@ -283,7 +283,9 @@ static int hp_sw_activate(struct scsi_de
> HP_SW_NAME);
> }
>
> - return ret;
> + if (fn)
> + fn(data, ret);
> + return 0;
> }
>
> static const struct scsi_dh_devlist hp_sw_dh_data_list[] = {
> Index: linux-2.6.31/include/scsi/scsi_device.h
> ===================================================================
> --- linux-2.6.31.orig/include/scsi/scsi_device.h
> +++ linux-2.6.31/include/scsi/scsi_device.h
> @@ -174,6 +174,7 @@ struct scsi_dh_devlist {
> char *model;
> };
>
> +typedef void (*activate_complete)(void *, int);
> struct scsi_device_handler {
> /* Used by the infrastructure */
> struct list_head list; /* list of scsi_device_handlers */
> @@ -185,7 +186,7 @@ struct scsi_device_handler {
> int (*check_sense)(struct scsi_device *, struct scsi_sense_hdr
> *);
> int (*attach)(struct scsi_device *);
> void (*detach)(struct scsi_device *);
> - int (*activate)(struct scsi_device *);
> + int (*activate)(struct scsi_device *, activate_complete, void *);
> int (*prep_fn)(struct scsi_device *, struct request *);
> };
>
> Index: linux-2.6.31/drivers/md/dm-mpath.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/md/dm-mpath.c
> +++ linux-2.6.31/drivers/md/dm-mpath.c
> @@ -1086,8 +1086,9 @@ static int pg_init_limit_reached(struct
> return limit_reached;
> }
>
> -static void pg_init_done(struct dm_path *path, int errors)
> +static void pg_init_done(void *data, int errors)
> {
> + struct dm_path *path = data;
> struct pgpath *pgpath = path_to_pgpath(path);
> struct priority_group *pg = pgpath->pg;
> struct multipath *m = pg->m;
> @@ -1153,12 +1154,11 @@ static void pg_init_done(struct dm_path
>
> static void activate_path(struct work_struct *work)
> {
> - int ret;
> struct pgpath *pgpath =
> container_of(work, struct pgpath, activate_path);
>
> - ret = scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev));
> - pg_init_done(&pgpath->path, ret);
> + scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
> + pg_init_done, &pgpath->path);
> }
>
> /*
> --
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