[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>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index 04c5cea47a22..506206ae5755 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/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,
 };