ipmi: Add a sysfs interface to view the number of users

A count of users is kept for each interface, allow it to be viewed.

Based on work by Chen Guanqiao <chen.chenchacha@foxmail.com>

Cc: Chen Guanqiao <chen.chenchacha@foxmail.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>

drivers/char/ipmi/ipmi_msghandler.c

@@ -457,6 +457,8 @@ struct ipmi_smi {
 	struct list_head users;
 	struct srcu_struct users_srcu;
 	atomic_t nr_users;
+	struct device_attribute nr_users_devattr;
+
 
 	/* Used for wake ups at startup. */
 	wait_queue_head_t waitq;
@@ -3506,6 +3508,17 @@ void ipmi_poll_interface(struct ipmi_user *user)
 }
 EXPORT_SYMBOL(ipmi_poll_interface);
 
+static ssize_t nr_users_show(struct device *dev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	struct ipmi_smi *intf = container_of(attr,
+			 struct ipmi_smi, nr_users_devattr);
+
+	return sysfs_emit(buf, "%d\n", atomic_read(&intf->nr_users));
+}
+static DEVICE_ATTR_RO(nr_users);
+
 static void redo_bmc_reg(struct work_struct *work)
 {
 	struct ipmi_smi *intf = container_of(work, struct ipmi_smi,
@@ -3628,6 +3641,12 @@ int ipmi_add_smi(struct module         *owner,
 	if (rv)
 		goto out_err_bmc_reg;
 
+	intf->nr_users_devattr = dev_attr_nr_users;
+	sysfs_attr_init(&intf->nr_users_devattr.attr);
+	rv = device_create_file(intf->si_dev, &intf->nr_users_devattr);
+	if (rv)
+		goto out_err_bmc_reg;
+
 	/*
 	 * Keep memory order straight for RCU readers.  Make
 	 * sure everything else is committed to memory before
@@ -3727,6 +3746,8 @@ void ipmi_unregister_smi(struct ipmi_smi *intf)
 
 	/* At this point no users can be added to the interface. */
 
+	device_remove_file(intf->si_dev, &intf->nr_users_devattr);
+
 	/*
 	 * Call all the watcher interfaces to tell them that
 	 * an interface is going away.