device: added register_class_devname() API

this allows drivers to register generic device names for a device
class, with automatic class instance handling

src/drivers/device/cdev.cpp

@@ -108,6 +108,42 @@ CDev::~CDev()
 		unregister_driver(_devname);
 }
 
+int
+CDev::register_class_devname(const char *class_devname)
+{
+	if (class_devname == nullptr) {
+		return -EINVAL;
+	}
+	int class_instance = 0;
+	int ret = -ENOSPC;
+	while (class_instance < 4) {
+		if (class_instance == 0) {
+			ret = register_driver(class_devname, &fops, 0666, (void *)this);
+			if (ret == OK) break;
+		} else {
+			char name[32];
+			snprintf(name, sizeof(name), "%s%u", class_devname, class_instance);
+			ret = register_driver(name, &fops, 0666, (void *)this);
+			if (ret == OK) break;
+		}
+		class_instance++;
+	}
+	if (class_instance == 4)
+		return ret;
+	return class_instance;
+}
+
+int
+CDev::unregister_class_devname(const char *class_devname, unsigned class_instance)
+{
+	if (class_instance > 0) {
+		char name[32];
+		snprintf(name, sizeof(name), "%s%u", class_devname, class_instance);
+		return unregister_driver(name);
+	}
+	return unregister_driver(class_devname);
+}
+
 int
 CDev::init()
 {

src/drivers/device/device.h

@@ -396,6 +396,25 @@ protected:
 	 */
 	virtual int	close_last(struct file *filp);
 
+        /**
+	 * Register a class device name, automatically adding device
+	 * class instance suffix if need be.
+	 *
+	 * @param class_devname   Device class name
+	 * @return class_instamce Class instance created, or -errno on failure
+	 */
+	virtual int register_class_devname(const char *class_devname);
+
+        /**
+	 * Register a class device name, automatically adding device
+	 * class instance suffix if need be.
+	 *
+	 * @param class_devname   Device class name
+	 * @param class_instance  Device class instance from register_class_devname()
+	 * @return		  OK on success, -errno otherwise
+	 */
+	virtual int unregister_class_devname(const char *class_devname, unsigned class_instance);
+
 private:
 	static const unsigned _max_pollwaiters = 8;
 
@@ -488,4 +507,7 @@ private:
 
 } // namespace device
 
+// class instance for primary driver of each class
+#define CLASS_DEVICE_PRIMARY 0
+
 #endif /* _DEVICE_DEVICE_H */