字符设备驱动不停打log 好像死循环了
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;
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.size= MEMDEV_SIZE;
mem_devp.data= kmalloc(MEMDEV_SIZE, GFP_KERNEL);
memset(mem_devp.data,0, MEMDEV_SIZE);
sema_init(&mem_devp.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");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;
/*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;
}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。 你程序中：/*写入设备*/
fwrite(Buf, sizeof(Buf), 1, fp0);应改为/*写入设备*/
fwrite(Buf, strlen(Buf), 1, fp0); ice2000feng 发表于 2012-03-06 11:23 static/image/common/back.gif
你程序中：应改为
是的 我也发觉了 但是我研究不出来 为什么sizeof（buf），也就是4096，可以导致驱动write函数不停的像死循环一样？
我直接把copy_from_user()的count数设置为4096也不会有这种效果的，为什么会不停打印出log ？谢谢 回复 3# win1naruto
第一次写了1024个字节，后面每次count先初始化为剩余的3072，但是又被改成mem_size-offset=0了，每次写0个字节，就写不完了。
因为没写完，又没出错，所以write一直被调用。代码只能保存1024个字节的内容，多了应该返回错误。
read读的字节可以比要求的少，write不一样。
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