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看了linux驱动开发详解书上的例子,网上找了代码,然后用这种方式一直是对的:- #include <linux/module.h>
- #include <linux/types.h>
- #include <linux/fs.h>
- #include <linux/errno.h>
- #include <linux/mm.h>
- #include <linux/sched.h>
- #include <linux/init.h>
- #include <linux/cdev.h>
- #include <asm/io.h>
- #include <asm/system.h>
- #include <asm/uaccess.h>
-
-
- #define MEMDEV_MAJOR 251 /*预设的mem的主设备号*/
- #define MEMDEV_NUM 2 /*设备数*/
- #define MEMDEV_SIZE 1024 //分配的内存大小
-
- struct mem_dev
- {
- unsignedint size;
- char*data;
- structsemaphore sem;
- };
-
- static int mem_major = MEMDEV_MAJOR; /*预设的mem的主设备号*/
- struct cdev mem_cdev;
- struct mem_dev *mem_devp; /*设备结构体指针*/
- /*文件打开函数*/
- static int mem_open(struct inode *inode,struct file *filp)
- {
- struct mem_dev *dev;
- unsignedint num;
-
- printk("mem_open.\n");
-
- num= MINOR(inode->i_rdev);//获得次设备号
- if(num> (MEMDEV_NUM -1)) //检查次设备号有效性
- return-ENODEV;
-
- dev= &mem_devp[num];
- filp->private_data= dev; //将设备结构保存为私有数据
-
- return0;
- }
-
- static int mem_release(struct inode *inode,struct file *filp)
- {
- printk("mem_release.\n");
- return0;
- }
-
- static ssize_t mem_read(struct file *filp,char __user *buf, size_t size, loff_t *ppos)
- {
- intret = 0;
- structmem_dev *dev;
- unsignedlong p;
- unsignedlong count;
-
- printk("mem_read.\n");
-
- dev= filp->private_data;//获得设备结构
- count= size;
- p= *ppos;
-
- //检查偏移量和数据大小的有效性
- if(p> MEMDEV_SIZE)
- return0;
- if(count> (MEMDEV_SIZE-p))
- count= MEMDEV_SIZE - p;
-
- if(down_interruptible(&dev->sem))//锁定互斥信号量
- return -ERESTARTSYS;
-
- //读取数据到用户空间
- if(copy_to_user(buf,dev->data+p, count)){
- ret= -EFAULT;
- printk("copyfrom user failed\n");
- }
- else{
- *ppos+= count;
- ret= count;
- printk("read%d bytes from dev\n", count);
- }
-
- up(&dev->sem);//解锁互斥信号量
-
- returnret;
- }
-
- static ssize_t mem_write(struct file *filp,const char __user *buf, size_t size, loff_t *ppos)//注意:第二个参数和read方法不同
- {
- intret = 0;
- structmem_dev *dev;
- unsignedlong p;
- unsignedlong count;
-
- printk("mem_write.\n");
-
- dev= filp->private_data;
- count= size;
- p= *ppos;
- printk("count : %d",count);
- if(p> MEMDEV_SIZE)
- return0;
- if(count> (MEMDEV_SIZE-p))
- count= MEMDEV_SIZE - p;
-
- if(down_interruptible(&dev->sem))//锁定互斥信号量
- return-ERESTARTSYS;
-
- if(copy_from_user(dev->data+p,buf, count)){
- ret= -EFAULT;
- printk("copyfrom user failed\n");
- }
- else{
- *ppos+= count;
- ret= count;
- printk("write%d bytes to dev\n", count);
- }
-
- up(&dev->sem);//解锁互斥信号量
-
- returnret;
- }
-
- static loff_t mem_llseek(struct file *filp,loff_t offset, int whence)
- {
- intnewpos;
-
- printk("mem_llseek.\n");
-
- switch(whence)
- {
- case0:
- newpos= offset;
- break;
-
- case1:
- newpos= filp->f_pos + offset;
- break;
-
- case2:
- newpos= MEMDEV_SIZE - 1 + offset;
- break;
-
- default:
- return-EINVAL;
- }
-
- if((newpos<0)|| (newpos>(MEMDEV_SIZE - 1)))
- return-EINVAL;
-
- filp->f_pos= newpos;
- returnnewpos;
- }
-
- /*文件操作结构体*/
- static const struct file_operations mem_fops = {
- .owner= THIS_MODULE,
- .open= mem_open,
- .write= mem_write,
- .read= mem_read,
- .release= mem_release,
- .llseek= mem_llseek,
- };
- /*设备驱动模块加载函数*/
- static int __init memdev_init(void)
- {
- int result;
- int err;
- int i;
-
- //申请设备号
- dev_t devno = MKDEV(mem_major, 0);
-
- if(mem_major)
- result= register_chrdev_region(devno, MEMDEV_NUM, "memdev");//注意静态申请的dev_t参数和动态dev_t参数的区别
- else{ //静态直接传变量,动态传变量指针
- result= alloc_chrdev_region(&devno, 0, MEMDEV_NUM, "memdev");
- mem_major= MAJOR(devno);
- }
-
- if(result< 0){
- printk("can'tget major devno:%d\n", mem_major);
- returnresult;
- }
-
- //注册设备驱动
- cdev_init(&mem_cdev,&mem_fops); /*初始化cdev结构*/
- mem_cdev.owner= THIS_MODULE;
-
- /* 注册字符设备 */
-
- err= cdev_add(&mem_cdev, MKDEV(mem_major, 0), MEMDEV_NUM);//如果有N个设备就要添加N个设备号
- if(err)
- printk("addcdev faild,err is %d\n", err);
-
- //分配设备内存
- mem_devp= kmalloc(MEMDEV_NUM*(sizeof(struct mem_dev)), GFP_KERNEL);
- if(!mem_devp){
- result = - ENOMEM;
- goto fail_malloc;
- }
- memset(mem_devp,0, MEMDEV_NUM*(sizeof(struct mem_dev)));
-
-
- for(i=0;i<MEMDEV_NUM; i++){
- mem_devp[i].size= MEMDEV_SIZE;
- mem_devp[i].data= kmalloc(MEMDEV_SIZE, GFP_KERNEL);
- memset(mem_devp[i].data,0, MEMDEV_SIZE);
- sema_init(&mem_devp[i].sem,1);//初始化互斥锁
- }
-
- returnresult;
-
- fail_malloc:
- unregister_chrdev_region(MKDEV(mem_major,0), MEMDEV_NUM);
- returnresult;
- }
-
- static void memdev_exit(void)
- {
- cdev_del(&mem_cdev);
- unregister_chrdev_region(MKDEV(mem_major,0), MEMDEV_NUM);//注意释放的设备号个数一定要和申请的设备号个数保存一致
- //否则会导致设备号资源流失
- printk("memdev_exit\n");
- }
-
- module_init(memdev_init);
- module_exit(memdev_exit);
-
- MODULE_AUTHOR("Y-Kee");
- MODULE_LICENSE("GPL");
复制代码 echo 'dddd'>/dev/memdev
cat /dev/memdev
但是用了自己写的测试程序就不行了:- #include <stdio.h>
- int main()
- {
- FILE *fp0 = NULL;
- char Buf[4096];
-
- /*初始化Buf*/
- strcpy(Buf,"Mem is char dev!");
- printf("BUF: %s\n",Buf);
-
- /*打开设备文件*/
- fp0 = fopen("/dev/memdev0","r+");
- if (fp0 == NULL)
- {
- printf("Open Memdev0 Error!\n");
- return -1;
- }
-
- /*写入设备*/
- fwrite(Buf, sizeof(Buf), 1, fp0);
-
- /*重新定位文件位置(思考没有该指令,会有何后果)*/
- fseek(fp0,0,SEEK_SET);
-
- /*清除Buf*/
- strcpy(Buf,"Buf is NULL!");
- printf("BUF: %s\n",Buf);
-
-
- /*读出设备*/
- fread(Buf, sizeof(Buf), 1, fp0);
-
- /*检测结果*/
- printf("BUF: %s\n",Buf);
-
- return 0;
- }
复制代码 不停打映出log :
[ 3721.809411] write 0 bytes to dev
[ 3721.809413] mem_write.
[ 3721.809615] count= 3072
[ 3721.809816] write 0 bytes to dev
[ 3721.809817] mem_write.
[ 3721.810018] count= 3072
[ 3721.810219] write 0 bytes to dev
[ 3721.810221] mem_write.
[ 3721.810422] count= 3072
为什么用fwrite的方式,count会这么大?3072 ?但是为什么会反复打印出log 、write()函数按道理只会执行一次的。 |
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