C - 字符驱动程序节点未打开

Question

我为我的 beaglebone 内核编写了一个简单的字符驱动程序

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/fs.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("[e-mail]");

#define  DEVICE_NAME "experm"
#define  CLASS_NAME  "exp"
static struct class*  myclass  = NULL; ///< The device-driver class struct pointer
static struct device* mychardevice = NULL; ///< The device-driver device struct pointer
static int myopen(struct inode *, struct file *);
static int release(struct inode *, struct file *);
static int myioctl(struct inode *, struct file *, unsigned int cmd, unsigned long arg);
static size_t myread(struct file *,char * , size_t,  loff_t *);
static size_t mywrite(struct file *,char * , size_t,  loff_t *);

static dev_t mydev;
static int myopen(struct inode *nd, struct file *fp)
{
printk(KERN_INFO "myopenn");
return 0;
}
static int myrelease(struct inode *nd, struct file *fp)
{
printk(KERN_INFO "myreleasen");
return 0;
}
static int myioctl(struct inode *nd, struct file *fp, unsigned int cmd, unsigned long arg)
{
printk(KERN_INFO "myioctln");
return 0;
}
static size_t myread(struct file *fp, char *buf, size_t len, loff_t *ofs)
{
printk(KERN_INFO "myreadn");
return 0;
}
static size_t mywrite(struct file *fp, char *buf, size_t len, loff_t *ofs)
{
printk(KERN_INFO "mywriten");
return 0;
}

static struct file_operations fops = {
.open = myopen,
.release = myrelease,
.read = myread,
.write = mywrite,
.unlocked_ioctl = myioctl,
};
static int __init myinit(void)
{
int err;
//extern int alloc_chrdev_region(dev_t *, unsigned minor number, unsigned total, const char *);
err = alloc_chrdev_region(&mydev, 0, 1, "expermdev");
if(err<0)
{
printk(KERN_INFO "major and minor can't be created, err = %dn", err);
return err;
}
//struct class * class_create ( struct module *owner, const char *name);
myclass = class_create(THIS_MODULE, CLASS_NAME);
if(IS_ERR(myclass))
{
unregister_chrdev(MAJOR(mydev), "expermdev");
printk(KERN_ALERT "Failed to register device classn");
return PTR_ERR(myclass); 
}
//struct device *device_create(struct class *cls, struct device *parent, dev_t devt, void *drvdata, const char *fmt, ...);
//This function can be used by char device classes. A struct device will be created in sysfs, registered to the specified class. 
mychardevice = device_create(myclass, NULL, mydev, NULL, "expermdev");
if(IS_ERR(mychardevice))
{
class_destroy(myclass);
unregister_chrdev(MAJOR(mydev), "expermdev");
printk(KERN_ALERT "Failed to create the devicen");
return PTR_ERR(mychardevice);
}
printk(KERN_INFO "my device created correctlyn");
return 0;
}
static void __exit myexit(void)
{
device_destroy(mychardevice, mydev);
class_unregister(myclass);
class_destroy(myclass);
unregister_chrdev(MAJOR(mydev), "expermdev");
printk(KERN_INFO "exitedn");
}
module_init(myinit);
module_exit(myexit);

和应用程序文件

#include <stdio.h>
#include<fcntl.h>
int main()
{
int fp;
fp = open ("/dev/expermdev", O_RDWR);
if(fp < 0)
printf("file can't be openedn");
else
printf("file openedn");
return 0;
}

我正在将驱动程序编译为模块并对其进行insmod，还使用相同的交叉编译器编译了 app.c，并将此二进制文件放在 bin 目录中。我运行了这个 bin 文件，但它说

file can't be opened

我做错了什么？

Answer 1

知道了。我没有使用 cdev 结构并向其添加了 fops。之后我必须告诉内核。

cdev = cdev_alloc();//allocate memory to Char Device structure
cdev->ops = &fops;//link our file operations to the char device
result=cdev_add(cdev,mydev,1);//Notify the kernel abt the new device

在取消注册驱动程序之前，还要在退出功能中删除此 CDV。 在register_chrdev_region我们同时做这两件事，但在主要和次要数字的动态分配中，我们必须使用 cdev 来完成其余的工作。