s3c2440 usb host device controller驱动分析（七）-----class driver_classdriver定义

      这里开始分析我们第一节贴的图中的class driver。class driver就是负责实现具体功能的driver，像usb-skeleton和usb鼠标的驱动。我认为class driver的功能应该是两个：一个是具体的操作usb device，实现具体的功能；二是像用户态提供dev的文件操作接口。

我们也用usb-skeleton为例进行分析。在这一层，还把usb device抽象成了一个设备 struct usb_skel dev。

/* Structure to hold all of our device specific stuff */
struct usb_skel {
	struct usb_device	*udev;			/* the usb device for this device */
	struct usb_interface	*interface;		/* the interface for this device */
	struct semaphore	limit_sem;		/* limiting the number of writes in progress */
	struct usb_anchor	submitted;		/* in case we need to retract our submissions */
	struct urb		*bulk_in_urb;		/* the urb to read data with */
	unsigned char      *bulk_in_buffer;	/* the buffer to receive data */
	size_t			bulk_in_size;		/* the size of the receive buffer */
	size_t			bulk_in_filled;		/* number of bytes in the buffer */
	size_t			bulk_in_copied;		/* already copied to user space */
	__u8			bulk_in_endpointAddr;	/* the address of the bulk in endpoint */
	__u8			bulk_out_endpointAddr;	/* the address of the bulk out endpoint */
	int			errors;			/* the last request tanked */
	int			open_count;		/* count the number of openers */
	bool			ongoing_read;		/* a read is going on */
	bool			processed_urb;		/* indicates we haven't processed the urb */
	spinlock_t		err_lock;		/* lock for errors */
	struct kref		kref;
	struct mutex		io_mutex;		/* synchronize I/O with disconnect */
	struct completion	bulk_in_completion;	/* to wait for an ongoing read */
};

我们看到，在class driver这一层，需要用到的gadget的信息就包含在udev、interface、bulk_in_endpointAddr、bulk_out_endpointAddr中，其实主要还是在interface中。

usb-skeleton.c中实现了两个driver。struct usb_driver skel_driver，struct usb_class_driver skel_class。