[SCSI] scsi_dh_alua: Inroduce the set_params interface scsi_dh_alua handler

Handler expects only one parameter to set the flag ALUA_OPTIMIZE_STPG.
This flag is used to optimize the STPG behaviour. There is no change in
behaviour by default.

For example, to set the flag pass the following parameters from multipath.conf
hardware_handler        "2 alua 1"
Signed-off-by: Babu Moger <babu.moger@netapp.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/device_handler/scsi_dh_alua.c

@@ -55,11 +55,15 @@
 #define ALUA_FAILOVER_TIMEOUT		(60 * HZ)
 #define ALUA_FAILOVER_RETRIES		5
 
+/* flags passed from user level */
+#define ALUA_OPTIMIZE_STPG		1
+
 struct alua_dh_data {
 	int			group_id;
 	int			rel_port;
 	int			tpgs;
 	int			state;
+	unsigned		flags; /* used for optimizing STPG */
 	unsigned char		inq[ALUA_INQUIRY_SIZE];
 	unsigned char		*buff;
 	int			bufflen;
@@ -621,6 +625,37 @@ static int alua_initialize(struct scsi_device *sdev, struct alua_dh_data *h)
 out:
 	return err;
 }
+/*
+ * alua_set_params - set/unset the optimize flag
+ * @sdev: device on the path to be activated
+ * params - parameters in the following format
+ *      "no_of_params\0param1\0param2\0param3\0...\0"
+ * For example, to set the flag pass the following parameters
+ * from multipath.conf
+ *     hardware_handler        "2 alua 1"
+ */
+static int alua_set_params(struct scsi_device *sdev, const char *params)
+{
+	struct alua_dh_data *h = get_alua_data(sdev);
+	unsigned int optimize = 0, argc;
+	const char *p = params;
+	int result = SCSI_DH_OK;
+
+	if ((sscanf(params, "%u", &argc) != 1) || (argc != 1))
+		return -EINVAL;
+
+	while (*p++)
+		;
+	if ((sscanf(p, "%u", &optimize) != 1) || (optimize > 1))
+		return -EINVAL;
+
+	if (optimize)
+		h->flags |= ALUA_OPTIMIZE_STPG;
+	else
+		h->flags &= ~ALUA_OPTIMIZE_STPG;
+
+	return result;
+}
 
 /*
  * alua_activate - activate a path
@@ -698,6 +733,7 @@ static struct scsi_device_handler alua_dh = {
 	.prep_fn = alua_prep_fn,
 	.check_sense = alua_check_sense,
 	.activate = alua_activate,
+	.set_params = alua_set_params,
 	.match = alua_match,
 };