Linux字符设备驱动
一、首先列出程序的全部源码
/root/drivers/freg
----freg.c
----freg.h
----Makefile
freg.h
#ifndef _FAKE_REG_H_
#define _FAKE_REG_H_
#include <linux/cdev.h>
#include <linux/semaphore.h>
#define FREG_DEVICE_NODE_NAME "freg"
#define FREG_DEVICE_FILE_NAME "freg"
#define FREG_DEVICE_PROC_NAME "freg"
#define FREG_DEVICE_CLASS_NAME "freg"
struct fake_reg_dev {
int val;
struct semaphore sem;
struct cdev dev;
};
#endif
freg.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/proc_fs.h>
#include <linux/device.h>
#include <asm/uaccess.h>
#include "freg.h"
static int freg_major = 0;
static int freg_minor = 0;
static struct class* freg_class = NULL;
static struct fake_reg_dev* freg_dev = NULL;
static int freg_open(struct inode* inode, struct file* filp);
static int freg_release(struct inode* inode, struct file* filp);
static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos);
static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos);
static struct file_operations freg_fops = {
.owner = THIS_MODULE,
.open = freg_open,
.release = freg_release,
.read = freg_read,
.write = freg_write,
};
static int freg_open(struct inode* inode, struct file* filp) {
struct fake_reg_dev* dev;
dev = container_of(inode->i_cdev, struct fake_reg_dev, dev);
filp->private_data = dev;
return 0;
}
static int freg_release(struct inode* inode, struct file* filp) {
return 0;
}
static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos) {
ssize_t err = 0;
struct fake_reg_dev* dev = filp->private_data;
if(down_interruptible(&(dev->sem))) {
return -ERESTARTSYS;
}
if(count < sizeof(dev->val)) {
goto out;
}
if(copy_to_user(buf, &(dev->val), sizeof(dev->val))) {
err = -EFAULT;
goto out;
}
err = sizeof(dev->val);
out:
up(&(dev->sem));
return err;
}
static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos) {
struct fake_reg_dev* dev = filp->private_data;
ssize_t err = 0;
if(down_interruptible(&(dev->sem))) {
return -ERESTARTSYS;
}
if(count != sizeof(dev->val)) {
goto out;
}
if(copy_from_user(&(dev->val), buf, count)) {
err = -EFAULT;
goto out;
}
err = sizeof(dev->val);
out:
up(&(dev->sem));
return err;
}
static int __freg_setup_dev(struct fake_reg_dev* dev) {
int err;
dev_t devno = MKDEV(freg_major, freg_minor);
memset(dev, 0, sizeof(struct fake_reg_dev));
cdev_init(&(dev->dev), &freg_fops);
dev->dev.owner = THIS_MODULE;
dev->dev.ops = &freg_fops;//回调函数
err = cdev_add(&(dev->dev),devno, 1);
if(err) {
return err;
}
init_MUTEX(&(dev->sem));//信号量
dev->val = 0;
return 0;
}
static int __init freg_init(void) {
int err = -1;
dev_t dev = 0;/一个32位的数，其中12位用来表示主设备号，而其余20位用来表示次设备号
struct device* temp = NULL;
printk(KERN_ALERT"Initializing freg device.\n");
err = alloc_chrdev_region(&dev, 0, 1, FREG_DEVICE_NODE_NAME);//动态分配主设备号和次设备号
if(err < 0) {
printk(KERN_ALERT"Failed to alloc char dev region.\n");
goto fail;
}
freg_major = MAJOR(dev);//获取主设备号
freg_minor = MINOR(dev);//获取次设备号
freg_dev = kmalloc(sizeof(struct fake_reg_dev), GFP_KERNEL);
if(!freg_dev) {
err = -ENOMEM;
printk(KERN_ALERT"Failed to alloc freg device.\n");
goto unregister;
}
err = __freg_setup_dev(freg_dev);
if(err) {
printk(KERN_ALERT"Failed to setup freg device: %d.\n", err);
goto cleanup;
}
freg_class = class_create(THIS_MODULE, FREG_DEVICE_CLASS_NAME);
if(IS_ERR(freg_class)) {
err = PTR_ERR(freg_class);
printk(KERN_ALERT"Failed to create freg device class.\n");
goto destroy_cdev;
}
temp = device_create(freg_class, NULL, dev, "%s", FREG_DEVICE_FILE_NAME);
if(IS_ERR(temp)) {
err = PTR_ERR(temp);
printk(KERN_ALERT"Failed to create freg device.\n");
goto destroy_class;
}
printk(KERN_ALERT"Succedded to initialize freg device.\n");
return 0;
destroy_class://错误处理机制
class_destroy(freg_class);
destroy_cdev:
cdev_del(&(freg_dev->dev));
cleanup:
kfree(freg_dev);
unregister:
unregister_chrdev_region(MKDEV(freg_major, freg_minor), 1);
fail:
return err;
}
static void __exit freg_exit(void) {
dev_t devno = MKDEV(freg_major, freg_minor);//获取dev_t变量
printk(KERN_ALERT"Destroy freg device.\n");
if(freg_class) {
device_destroy(freg_class, MKDEV(freg_major,freg_minor));//删除/dev/freg文件
class_destroy(freg_class);
}
if(freg_dev) {//删除字符设备
cdev_del(&(freg_dev->dev));
kfree(freg_dev);
}
unregister_chrdev_region(devno, 1);//取消原来申请的主设备号和次设备号
}
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Fake Register Driver");//如果是android内核源码中,make menuconfig出现的界面会有此项
module_init(freg_init);//insmod执行这个函数
module_exit(freg_exit);//rmmod执行这个函数
Makefile
obj-m :=freg.o
第1步：建立Linux驱动骨架（装载和卸载Linux驱动）
任何类型的程序都需要一个开始执行的函数，比如C语言需要一个main函数，Linux提供两个函数module_init和module_exit来分别处理驱动程序的初始化和退出。module_init相当于C语言的main函数。
module_init(freg_init); module_exit(freg_exit);
第2步：注册和注销设备文件
注册设备文件在本程序中分为3小步：
1、动态分配主设备号和次设备号；
dev_t dev = 0; err = alloc_chrdev_region(&dev, 0, 1, FREG_DEVICE_NODE_NAME);//动态分配主设备号和次设备号dev_t是一个32位的数，其中12位用来表示主设备号，而其余20位用来表示次设备号。
MAJOR(dev_t dev)用来获取主设备号，MINOR(dev_t dev)用来获取次设备号。
MKDEV(int major,int minor)将主设备号和次设备号转换成dev_t类型。
2、根据得到的主设备号和次设备号注册字符设备；
static int __freg_setup_dev(struct fake_reg_dev* dev) {
int err;
dev_t devno = MKDEV(freg_major, freg_minor);
memset(dev, 0, sizeof(struct fake_reg_dev));
cdev_init(&(dev->dev), &freg_fops);
dev->dev.owner = THIS_MODULE;
dev->dev.ops = &freg_fops;
err = cdev_add(&(dev->dev),devno, 1);
if(err) {
return err;
}
init_MUTEX(&(dev->sem));
dev->val = 0;
return 0;
}
3、为驱动程序建立文件/dev/freg，来操作字符设备驱动。
freg_class = class_create(THIS_MODULE, FREG_DEVICE_CLASS_NAME);
if(IS_ERR(freg_class)) {
err = PTR_ERR(freg_class);
printk(KERN_ALERT"Failed to create freg device class.\n");
goto destroy_cdev;
}
temp = device_create(freg_class, NULL, dev, "%s", FREG_DEVICE_FILE_NAME);
if(IS_ERR(temp)) {
err = PTR_ERR(temp);
printk(KERN_ALERT"Failed to create freg device.\n");
goto destroy_class;
}
前面3步的逆操作。
static void __exit freg_exit(void) {
dev_t devno = MKDEV(freg_major, freg_minor);
printk(KERN_ALERT"Destroy freg device.\n");
if(freg_class) {
device_destroy(freg_class, MKDEV(freg_major,freg_minor));
class_destroy(freg_class);
}
if(freg_dev) {
cdev_del(&(freg_dev->dev));
kfree(freg_dev);
}
unregister_chrdev_region(devno, 1);
}
第3步：指定与驱动相关信息
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Fake Register Driver");
static int freg_open(struct inode* inode, struct file* filp);
static int freg_release(struct inode* inode, struct file* filp);
static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos);
static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos);
static struct file_operations freg_fops = {
.owner = THIS_MODULE,
.open = freg_open,
.release = freg_release,
.read = freg_read,
.write = freg_write,
};
static int freg_open(struct inode* inode, struct file* filp) {
struct fake_reg_dev* dev;
dev = container_of(inode->i_cdev, struct fake_reg_dev, dev);
filp->private_data = dev;
return 0;
}
static int freg_release(struct inode* inode, struct file* filp) {
return 0;
}
static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos) {
ssize_t err = 0;
struct fake_reg_dev* dev = filp->private_data;
if(down_interruptible(&(dev->sem))) {
return -ERESTARTSYS;
}
if(count < sizeof(dev->val)) {
goto out;
}
if(copy_to_user(buf, &(dev->val), sizeof(dev->val))) {
err = -EFAULT;
goto out;
}
err = sizeof(dev->val);
out:
up(&(dev->sem));
return err;
}
static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos) {
struct fake_reg_dev* dev = filp->private_data;
ssize_t err = 0;
if(down_interruptible(&(dev->sem))) {
return -ERESTARTSYS;
}
if(count != sizeof(dev->val)) {
goto out;
}
if(copy_from_user(&(dev->val), buf, count)) {
err = -EFAULT;
goto out;
}
err = sizeof(dev->val);
out:
up(&(dev->sem));
return err;
} 可能有的读者注意到了。freg.c中的所有函数、变量都声明成了static。这是因为在C语言中用static声明函数、变量等资源，系统会将这些函数和变量单独放在内存的某一个区域，直到程序完全退出，否则这些资源不会被释放。Linux驱动一旦装载，除非手动卸载或关机，驱动会一直驻留内存，因此这些函数和变量资源会一直在内存中。也就是说多次调用这些资源不用再进行压栈、出栈操作了。有利于提高驱动的运行效率。
第5步：编写MakeFile文件
obj-m :=freg.o
第6步：编译Linux驱动模块
sudo su 进入root模式
make -C /usr/src/linux-headers-2.6.32-21-generic/ M=/root/drivers/freg/
第7步：安装和卸载Linux驱动
安装freg驱动：
cd /root/drivers/freg/
insmod freg.ko
查看freg是否成功安装：
lsmod | grep freg
显示如下：
freg 2188 0
查看/dev/freg信息
ls -l /dev/freg
显示如下：
crw-rw---- 1 root root 248, 0 2014-06-06 23:50 /dev/freg
卸载Linux驱动
rmmod freg
查看由Linux驱动输出的日志信息
dmesg | grep freg
最后三行，显示如下：
[ 7722.273680] Initializing freg device. [ 7722.274095] Succedded to initialize freg device. [10766.282006] Destroy freg device.
三、编写C语言程序验证freg驱动程序
/root/drivers/freg
----hello.c
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#define DEVICE_NAME "/dev/freg"
int main(int argc, char** argv)
{
int fd = -1;
int val = 0;
fd = open(DEVICE_NAME, O_RDWR);
if(fd == -1) {
printf("Failed to open device %s.\n", DEVICE_NAME);
return -1;
}
printf("Read original value:\n");
read(fd, &val, sizeof(val));
printf("%d.\n\n", val);
val = 5;
printf("Write value %d to %s.\n\n", val, DEVICE_NAME);
write(fd, &val, sizeof(val));
printf("Read the value again:\n");
read(fd, &val, sizeof(val));
printf("%d.\n\n", val);
close(fd);
return 0;
}
编译gcc hello.c -o hello
运行./hello，结果如下：
Read original value: 0. Write value 5 to /dev/freg. Read the value again: 5.