cciss: Add usage_count attribute to each logical drive in /sys

Add usage_count attribute to each logical drive at
/sys/devices/<dev>/ccissX/cXdY/usage_count for controller X,
logical drive Y.  The usage count is the number of times
the device has currently been opened.
Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Documentation/ABI/testing/sysfs-bus-pci-devices-cciss

@@ -52,3 +52,10 @@ Kernel Version: 2.6.31
 Contact:	iss_storagedev@hp.com
 Description:	Displays the RAID level of logical drive Y of
 		controller X.
+
+Where:		/sys/bus/pci/devices/<dev>/ccissX/cXdY/usage_count
+Date:		August 2009
+Kernel Version: 2.6.31
+Contact:	iss_storagedev@hp.com
+Description:	Displays the usage count (number of opens) of logical drive Y
+		of controller X.

drivers/block/cciss.c

@@ -626,6 +626,25 @@ static ssize_t cciss_show_raid_level(struct device *dev,
 }
 DEVICE_ATTR(raid_level, S_IRUGO, cciss_show_raid_level, NULL);
 
+static ssize_t cciss_show_usage_count(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	drive_info_struct *drv = dev_get_drvdata(dev);
+	struct ctlr_info *h = to_hba(drv->dev->parent);
+	unsigned long flags;
+	int count;
+
+	spin_lock_irqsave(CCISS_LOCK(h->ctlr), flags);
+	if (h->busy_configuring) {
+		spin_unlock_irqrestore(CCISS_LOCK(h->ctlr), flags);
+		return -EBUSY;
+	}
+	count = drv->usage_count;
+	spin_unlock_irqrestore(CCISS_LOCK(h->ctlr), flags);
+	return snprintf(buf, 20, "%d\n", count);
+}
+DEVICE_ATTR(usage_count, S_IRUGO, cciss_show_usage_count, NULL);
+
 static struct attribute *cciss_host_attrs[] = {
 	&dev_attr_rescan.attr,
 	NULL
@@ -653,6 +672,7 @@ static struct attribute *cciss_dev_attrs[] = {
 	&dev_attr_rev.attr,
 	&dev_attr_lunid.attr,
 	&dev_attr_raid_level.attr,
+	&dev_attr_usage_count.attr,
 	NULL
 };