Linux操作系统内核和设备文件对话(1)(5)

/* Module Declarations *************************** */

/* This structure will hold the functions to be called

* when a process does something to the device we

* created. Since a pointer to this structure is kept in

* the devices table, it cant be local to

* init_module. NULL is for unimplemented functions. */

struct file_operations Fops = {

NULL, /* seek */

device_read,

device_write,

NULL, /* readdir */

NULL, /* select */

device_ioctl, /* ioctl */

NULL, /* mmap */

device_open,

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

NULL, /* flush */

#endif

device_release /* a.k.a. close */

};

/* Initialize the module - Register the character device */

int init_module()

{

int ret_val;

/* Register the character device (atleast try) */

ret_val = module_register_chrdev(MAJOR_NUM,

DEVICE_NAME,

&Fops);

/* Negative values signify an error */

if (ret_val < 0) {

printk ("%s failed with %d\n",

"Sorry, registering the character device ",

ret_val);

return ret_val;

}

printk ("%s The major device number is %d.\n",

"Registeration is a success",

MAJOR_NUM);

printk ("If you want to talk to the device driver,\n");

printk ("youll have to create a device file. \n");

printk ("We suggest you use:\n");

printk ("mknod %s c %d 0\n", DEVICE_FILE_NAME,

MAJOR_NUM);

printk ("The device file name is important, because\n");

printk ("the ioctl program assumes thats the\n");

printk ("file youll use.\n");

return 0;

}

/* Cleanup - unregister the appropriate file from /proc */

void cleanup_module()

{

int ret;

/* Unregister the device */

ret = module_unregister_chrdev(MAJOR_NUM, DEVICE_NAME);

/* If theres an error, report it */

if (ret < 0)

printk("Error in module_unregister_chrdev: %d\n", ret);

}

ex chardev.h

/* chardev.h - the header file with the ioctl definitions.

*

* The declarations here have to be in a header file,

* because they need to be known both to the kernel

* module (in chardev.c) and the process calling ioctl

* (ioctl.c)

*/

#ifndef CHARDEV_H

#define CHARDEV_H

#include

/* The major device number. We cant rely on dynamic

* registration any more, because ioctls need to know

* it. */

#define MAJOR_NUM 100

/* Set the message of the device driver */

#define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *)

/* _IOR means that were creating an ioctl command

* number for passing information from a user process

* to the kernel module.