linux驱动例子

• Makefile

obj-m := test.o
KERNELDIR := /lib/modules/$(shell uname -r)/build
PWD       := $(shell pwd)
default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

• test.c

#include <linux/types.h> /*基本的类型定义*/
#include <linux/fs.h> /*文件系统使用相关的头文件*/
#include <linux/mm.h>
#include <linux/errno.h>
#include <asm/segment.h>
#include <asm/uaccess.h>
#include <linux/module.h>
unsigned int test_major = 0;
static int read_test(struct file *file, const char __user *buf,size_t count, loff_t *ppos){
printk(KERN_INFO "test read\n"); 
  int left=0;
  if (access_ok(VERIFY_WRITE, buf, count)){
  for(left=count;left>0;left--){
    __put_user('a', buf);
    buf++;
   }
}
  return count;
}
static int write_test(struct file *file, const char __user *buf,size_t count, loff_t *ppos)//(struct inode *inode, struct file *file, const char *buf,int*count)
{ //33
    printk(KERN_INFO "test write %d\n",count); 
  return count; 
} 
static int open_test(struct inode *inode, struct file *file ){ //36
  //MOD_INC_USE_COUNT; /*模块计数加1，表示当前内核有个设备加载内核当中去*/
printk(KERN_INFO "test open\n"); 
   try_module_get(THIS_MODULE);
   return 0; 
} 
static void release_test(struct inode *inode, struct file *file ){ //41
  //MOD_DEC_USE_COUNT; 
printk(KERN_INFO "test release\n"); 
  module_put(THIS_MODULE);
} 
struct file_operations test_fops=
{
 .owner    = THIS_MODULE,
 .read     = read_test,
 .write    = write_test,
 .open     = open_test,
 .release  = release_test,
};


int init_module(void){ 
    printk(KERN_INFO "test driver\n"); 
  int result;  
  result = register_chrdev(0, "test", &test_fops);/*对设备操作的整个接口*/
  if (result < 0){ 
    printk(KERN_INFO "test: can't get major number\n"); 
    return result; 
  } 
  if (test_major == 0)
    test_major = result; /* dynamic */ 
    return 0; 
}



void cleanup_module(void){ 
printk(KERN_INFO "test driver 88\n"); 
  unregister_chrdev(test_major, "test"); 
}



insmod -f test.ko

sudo insmod -f test.ko
cat /proc/devices (获得250的值)
sudo mknod /dev/test c 250 0

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
void main ()
{
    int sdc=open("/dev/test",O_RDWR);
    char buf[512]={0};
    int count=0;
    count=read(sdc,buf,512);
    printf("%d %s %d",sdc,buf,count);

//    lseek(sdc,0 ,SEEK_SET);
    count =  write(sdc,buf,512);
    printf("write %d %x\n",count,buf[0]);
    close(sdc);}