5.3.2. Device numbers

• major and minor numbers
• used by kernel to identify driver that handles request
• many statically assigned (Documentation/devices.txt) (but no new ones will be)
• need to be allocated (=claimed)
• static or dynamic allocation
• mapping number -> device can vary (1:1, n:1)

API: Device numbers

type:

dev_t

include/linux/types.h

creation, accessors:

MKDEV(int major, int minor)
MAJOR(dev_t dev)
MINOR(dev_t dev)

include/linux/kdev_t.h

register a (known) range of numbers:

int register_chrdev_region(dev_t first, unsigned int count, char *name);

• first: first number in range
• count: how many minor numbers?
• name: name of device

allocate a range of free numbers:

int alloc_chrdev_region(dev_t *dev, unsigned int firstminor, unsigned int count, char *name);

• dev: pointer to existing dev_t, will contain allocated major/minor
• firstminor: usually 0 (but not required)
• name: name of device

free allocated or registered range of numbers:

void unregister_chrdev_region(dev_t first, unsigned int count);

include/linux/fs.h