What Special Files Are

The ChorusOS system requires you to use special(7S) device driver files to access the hardware devices where file systems reside. This means that disk labeling and other operations on uninitialized and unmounted file systems must be done using special files.

Each disk partition corresponds to at least one special file. Unless you plan to use a raw partition directly -- without a file system-- you must be able to access each partition in both block (buffered) mode and raw (character) mode, so you must create not just one special file per partition, but two. Each special file:

• Refers to either a block or a raw device. Block devices are used by file systems. Raw devices are used primarily for file system administration.

• Has a major number. Major numbers are used by the system to select the corresponding device driver when several devices are configured. Major numbers are the same for all devices managed by a given device driver and a given access method (raw or block). For example, all devices corresponding to hard disk partitions using raw mode have the same major number.

• Has a minor number. Minor numbers are not used directly by the system, but by the selected device driver. Minor numbers are different for each partition on a device. Their scope is limited to the device described by the major number, so special files with different major numbers may share the same minor number. One minor number corresponds to one partition.