linux驱动_开发字符型设备驱动-优快云博客

本文链接：https://blog.youkuaiyun.com/huuuerli/article/details/127947614

首先我们得有一个注册函数和一个注销函数。代表着设备的注册与注销。

我们分别使用以下两个函数进行实现。

        static inline int register_chrdev(unsigned int major, const char *name,
                                                                const struct file_operations *fops)

        static inline void unregister_chrdev(unsigned int major, const char *name)

通过调用这两个函数来实现我们的注册与注销。

static int __init chrdevbase_init(void)
{
        int ret = 0;
        ret = register_chrdev(CHRDEVBASE_MAJOR,CHRDEVBASE_NAME, &chrdevbase_fops);
        if (ret<0)
        {
        printk("register devices failed\r\n");
          return -1;
          }
          else
          {
          printk("register devices success\r\n");
          }
          return 0 ;
}

static void __exit chrdevbase_exit(void)
{
unregister_chrdev(CHRDEVBASE_MAJOR,CHRDEVBASE_NAME);
printk("unregister devices success\r\n");
}

/* 将上面两个函数指定为驱动的入口和出口函数 */

module_init(chrdevbase_init);
module_exit(chrdevbase_exit);

还需要定义两个变量，一个是设备号，一个是设备名

#define CHRDEVBASE_MAJOR 201
#define CHRDEVBASE_NAME "chrdevbase"

通过这个 file_operations 结构体我们去实现我们自己的操作函数。

比如我们要实现读、写、开、关。

struct file_operations {
            struct module *owner;
            loff_t (*llseek) (struct file *, loff_t, int);
            ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
            ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
            ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
            ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
           int (*iopoll)(struct kiocb *kiocb, bool spin);
           int (*iterate) (struct file *, struct dir_context *);
           int (*iterate_shared) (struct file *, struct dir_context *);
           __poll_t (*poll) (struct file *, struct poll_table_struct *);
           long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
           long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
           int (*mmap) (struct file *, struct vm_area_struct *);
           unsigned long mmap_supported_flags;
           int (*open) (struct inode *, struct file *);
           int (*flush) (struct file *, fl_owner_t id);
            int (*release) (struct inode *, struct file *);
           int (*fsync) (struct file *, loff_t, loff_t, int datasync);
           int (*fasync) (int, struct file *, int);
           int (*lock) (struct file *, int, struct file_lock *);
           ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
            unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
           int (*check_flags)(int);
           int (*flock) (struct file *, int, struct file_lock *);
           ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
           ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
           int (*setlease)(struct file *, long, struct file_lock **, void **);
           long (*fallocate)(struct file *file, int mode, loff_t offset,
           loff_t len);
           void (*show_fdinfo)(struct seq_file *m, struct file *f);

实现上方功能我们就需要创建自己的一个结构体。其中开关读写的函数都需要我们自己来实现。

static struct file_operations chrdevbase_fops = {
        .owner = THIS_MODULE,
          .open = chrdevbase_open,
          .read = chrdevbase_read,
          .write = chrdevbase_write,
          .release = chrdevbase_release,
};

下方函数就是我们需要来实现的，printk后面一定要跟 \r\n 不然会出错 printk是内核态中的打印函数。

static int chrdevbase_open(struct inode *inode, struct file *file)
{
printk("chrdevbase_open\r\n");//内核态打印函数
return 0;
}

static ssize_t chrdevbase_read(struct file *file, char __user *buf, size_t count, loff_t *offt)
{
printk("chrdevbase_read\r\n");//内核态打印函数
return 0;
}

static ssize_t chrdevbase_write(struct file *file, const char __user *buf, size_t count, loff_t *offt)
{
printk("chrdevbase_write\r\n");//内核态打印函数
return 0;
}

static int chrdevbase_release(struct inode *inode, struct file *file)
{
printk("chrdevbase_release\r\n");//内核态打印函数
return 0;
}

编写完成后就要编译，在编译之前需要编写Makefile文件

KERNELDIR := /home/huerli/linux/atk-mp1/linux/y_linux/linux-5.4.31/
CURRENT_PATH := $(shell pwd)

obj-m := chrdevbase.o

build: kernel_modules

kernel_modules:
$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modules
clean:
$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean

KERNELDIR是linux源码目录。需要修改为自己的源码目录。

编译