Whats this major/minor device number thing?
• (REG) Device numbers are the traditional Unix way to provide a mapping between the filesystem and device drivers. A device number is a combination of a major number and a minor number. Currently Linux has 8 bit majors and minors. When you open a device file (character or block device) the kernel takes the major number from the inode and indexes into a table of driver structure pointers. The specific driver structure is then used to call the driver open() method, which in turn may interpret the minor number. There are two tables: one for character devices and one for block devices, each are 256 entries maximum. Obviously, there must be agreement between device numbers used in a driver and files in /dev. The kernel source has the file Documentation/devices.tex which lists all the official major and minor numbers. H. Peter Anvin (HPA) maintains this list. If you write a new driver (for public consumption), you will need to get a major number allocated by HPA. See the Q/A on devfs for an
