scsi_dh_alua: do not fail for unknown VPD identification

Not every device will return a useable VPD identification, but still
might support ALUA. Rather than disable ALUA support we should be
allowing the device identification to be empty and attach individual
ALUA device handler to each devices.

[mkp: Fixed typo reported by Bart]

Reported-by: Paul Mackerras <[e-mail]>
Signed-off-by: Hannes Reinecke <[e-mail]>
Tested-by: Paul Mackerras <[e-mail]>
Reviewed-by: Bart Van Assche <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/device_handler/scsi_dh_alua.c

···
 {
 	struct alua_port_group *pg;
 
+	if (!id_str || !id_size || !strlen(id_str))
+		return NULL;
+
 	list_for_each_entry(pg, &port_group_list, node) {
 		if (pg->group_id != group_id)
 			continue;
-		if (pg->device_id_len != id_size)
+		if (!pg->device_id_len || pg->device_id_len != id_size)
 			continue;
 		if (strncmp(pg->device_id_str, id_str, id_size))
 			continue;
···
 					    sizeof(pg->device_id_str));
 	if (pg->device_id_len <= 0) {
 		/*
-		 * Internal error: TPGS supported but no device
-		 * identifcation found. Disable ALUA support.
+		 * TPGS supported but no device identification found.
+		 * Generate private device identification.
 		 */
-		kfree(pg);
 		sdev_printk(KERN_INFO, sdev,
 			    "%s: No device descriptors found\n",
 			    ALUA_DH_NAME);
-		return ERR_PTR(-ENXIO);
+		pg->device_id_str[0] = '\0';
+		pg->device_id_len = 0;
 	}
 	pg->group_id = group_id;
 	pg->tpgs = tpgs;
···
 			return SCSI_DH_NOMEM;
 		return SCSI_DH_DEV_UNSUPP;
 	}
-	sdev_printk(KERN_INFO, sdev,
-		    "%s: device %s port group %x rel port %x\n",
-		    ALUA_DH_NAME, pg->device_id_str, group_id, rel_port);
+	if (pg->device_id_len)
+		sdev_printk(KERN_INFO, sdev,
+			    "%s: device %s port group %x rel port %x\n",
+			    ALUA_DH_NAME, pg->device_id_str,
+			    group_id, rel_port);
+	else
+		sdev_printk(KERN_INFO, sdev,
+			    "%s: port group %x rel port %x\n",
+			    ALUA_DH_NAME, group_id, rel_port);
 
 	/* Check for existing port group references */
 	spin_lock(&h->pg_lock);