USB device driver Major No. Minor NO. neccesity?

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http://www.linuxquestions.org – Dear sir, Is it necessary allocate Major no. Minor No. specifically in USB driver code. i have confusion. because even i have example code from net its not allocating any kind of major or Minor nos. Its just giving base minor no. in following kernel struct struct usb_class_driver in usb.h Code: struct usb_class_driver {         char *name;         char *(*devnode)(struct device *dev, mode_t *mode);         const struct file_operations *fops;         int minor_base; }; what is reality what is right? thanks &am (HowTos)