Linux Device Drivers | Char Drivers

<linux/types.h>

dev_t

dev_t is the type used to represent device numbers within the kernel.

int MAJOR(dev_t dev);
int MINOR(dev_t dev);

Macros that extract the major and minor numbers from a device number.

dev_t MKDEV(unsigned int major, unsigned int minor);

Macro that builds a dev_t data item from the major and minor numbers.

<linux/fs.h>

The “filesystem” header is the header required for writing device drivers. Many important functions and data structures are declared in here.

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

Functions that allow a driver to allocate and free ranges of device numbers. register_chrdev_region should be used when the desired major number is known in advance; for dynamic allocation, use alloc_chrdev_region instead.

int register_chrdev(unsigned int major, const char *name, struct file_operations *fops);

The old (pre-2.6) char device registration routine. It is emulated in the 2.6 kernel but should not be used for new code. If the major number is not 0, it is used unchanged; otherwise a dynamic number is assigned for this device.

int unregister_chrdev(unsigned int major, const char *name);

Function that undoes a registration made with register_chrdev. Both major and the name string must contain the same values that were used to register the driver.

struct file_operations;
struct file;
struct inode;

Three important data structures used by most device drivers. The file_operations structure holds a char driver’s methods; struct file represents an open file, and struct inode represents a file on disk.

<linux/cdev.h>

struct cdev *cdev_alloc(void);
void cdev_init(struct cdev *dev, struct file_operations *fops);
int cdev_add(struct cdev *dev, dev_t num, unsigned int count);
void cdev_del(struct cdev *dev);

Functions for the management of cdev structures, which represent char devices within the kernel.

<linux/kernel.h>

container_of(pointer, type, field);

A convenience macro that may be used to obtain a pointer to a structure from a pointer to some other structure contained within it.

<asm/uaccess.h>

This include file declares functions used by kernel code to move data to and from user space.

unsigned long copy_from_user (void *to, const void *from, unsigned long count);
unsigned long copy_to_user (void *to, const void *from, unsigned long count);

Copy data between user space and kernel space.