《韦东山新视频 — hello驱动（不涉及硬件）》

int open(const char *pathname, int flags, mode_t mode);

#include <linux/module.h>

#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>

/* 1. 确定主设备号                                                                 */
static int major = 0;
static char kernel_buf[1024];
static struct class *hello_class;


#define MIN(a, b) (a < b ? a : b)

/* 3. 实现对应的open/read/write等函数，填入file_operations结构体                   */
static ssize_t hello_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
    int err;
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    err = copy_to_user(buf, kernel_buf, MIN(1024, size));
    return MIN(1024, size);
}

static ssize_t hello_drv_write (struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
    int err;
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    err = copy_from_user(kernel_buf, buf, MIN(1024, size));
    return MIN(1024, size);
}

static int hello_drv_open (struct inode *node, struct file *file)
{
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    return 0;
}

static int hello_drv_close (struct inode *node, struct file *file)
{
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    return 0;
}

/* 2. 定义自己的file_operations结构体                                              */
static struct file_operations hello_drv = {
    .owner     = THIS_MODULE,
    .open    = hello_drv_open,
    .read    = hello_drv_read,
    .write   = hello_drv_write,
    .release = hello_drv_close,
};

/* 4. 把file_operations结构体告诉内核：注册驱动程序                                */
/* 5. 谁来注册驱动程序啊？得有一个入口函数：安装驱动程序时，就会去调用这个入口函数 */
static int __init hello_init(void)
{
    int err;
    
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    major = register_chrdev(0, "hello", &hello_drv);  /* /dev/hello */


    hello_class = class_create(THIS_MODULE, "hello_class");
    err = PTR_ERR(hello_class);
    if (IS_ERR(hello_class)) {
        printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
        unregister_chrdev(major, "hello");
        return -1;
    }
    
    device_create(hello_class, NULL, MKDEV(major, 0), NULL, "hello"); /* /dev/hello */
    
    return 0;
}

/* 6. 有入口函数就应该有出口函数：卸载驱动程序时，就会去调用这个出口函数           */
static void __exit hello_exit(void)
{
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    device_destroy(hello_class, MKDEV(major, 0));
    class_destroy(hello_class);
    unregister_chrdev(major, "hello");
}


/* 7. 其他完善：提供设备信息，自动创建设备节点                                     */

module_init(hello_init);
module_exit(hello_exit);

MODULE_LICENSE("GPL");

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

/*
 * ./hello_drv_test -w abc
 * ./hello_drv_test -r
 */
int main(int argc, char **argv)
{
    int fd;
    char buf[1024];
    int len;
    
    /* 1. 判断参数 */
    if (argc < 2) 
    {
        printf("Usage: %s -w <string>\n", argv[0]);
        printf("       %s -r\n", argv[0]);
        return -1;
    }

    /* 2. 打开文件 */
    fd = open("/dev/hello", O_RDWR);
    if (fd == -1)
    {
        printf("can not open file /dev/hello\n");
        return -1;
    }

    /* 3. 写文件或读文件 */
    if ((0 == strcmp(argv[1], "-w")) && (argc == 3))
    {
        len = strlen(argv[2]) + 1;
        len = len < 1024 ? len : 1024;
        write(fd, argv[2], len);
    }
    else
    {
        len = read(fd, buf, 1024);        
        buf[1023] = ‘\0‘;
        printf("APP read : %s\n", buf);
    }
    
    close(fd);
    
    return 0;
}

# 1. 使用不同的开发板内核时, 一定要修改KERN_DIR
# 2. KERN_DIR中的内核要事先配置、编译, 为了能编译内核, 要先设置下列环境变量:
# 2.1 ARCH,          比如: export ARCH=arm64
# 2.2 CROSS_COMPILE, 比如: export CROSS_COMPILE=aarch64-linux-gnu-
# 2.3 PATH,          比如: export PATH=$PATH:/home/book/100ask_roc-rk3399-pc/ToolChain-6.3.1/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin 
# 注意: 不同的开发板不同的编译器上述3个环境变量不一定相同,
#       请参考各开发板的高级用户使用手册

KERN_DIR = /home/book/100ask_roc-rk3399-pc/linux-4.4

all:
    make -C $(KERN_DIR) M=`pwd` modules 
    $(CROSS_COMPILE)gcc -o hello_drv_test hello_drv_test.c 

clean:
    make -C $(KERN_DIR) M=`pwd` modules clean
    rm -rf modules.order
    rm -f hello_drv_test

obj-m    += hello_drv.o