linux device driver 3rd (kernel 2.6.x) 笔记1

(chapter 3)

The internal representation of Device number

type: dev_t (define in <linux/types.h>)

dev_t: 32bit total whit 12 bit for major number, 20 bit for minor number.

some macros define in <linux/kdev_t.h>:

MAJOR(dev_t dev);

MINOR(dev_t dev);

// return major/minor number of a devt.

MKDEV(int major, int minor); // This funtion turn major num and minor num into dev_t.

Allocating and freeing device number

To obtain one or more device number

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

//declared in <linux/fs.h>

allocate device number from first to first+count-1

int alloc_chrdev_region(dev_t *dev, unsigned int firstminor,

unsigned int count, char *name);

void unregister_chrdev_region(dev_t first, unsigned int count);

Dynomic allocation of major number

Some major device numbers are statically assigned to the most common devices.

A list of those device can be found in Documentation/devices.txt