Hello World driver (II) - primary version

hello world drive （ One ） About a simple hello world The implementation of the driver , This time, the implementation and application of file operation interface are added on the original basis .（2022/07/23 21:27）
It's a fantastic dream , Can't resist silly persistence ！

makefile unchanged ,hello demo New file operation interface , as follows

test demo

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#include <linux/init.h> // This header file contains the functions for initializing and clearing your module
#include <linux/module.h> // This header file contains many definitions of symbols and functions , These symbols and functions are mostly related to loading modules
#include <linux/kernel.h>
#include <linux/fs.h>

#ifdef MODULE_NAME
#unfine MODULE_NAME
#endif
#define MODULE_NAME “bgm_str_dev”

static int hello_open(struct inode *inode, struct file *file)
{
printk(“hello open!\n”);
// open You can save your private data in private_data Pointer , So in read_write When , You can also access the corresponding data through this pointer
// Sometimes it is necessary to identify the secondary equipment number
// file->private_data = pdata;
return 0;
}

static ssize_t hello_read(struct file *filp, char __user * buf, size_t size, loff_t * off)
{
printk(“hello read!\n”);
return 0;
}

static ssize_t hello_write (struct file *filp, const char __user *buf, size_t size, loff_t * off)
{
printk(“hello write!\n”);
return 0;
}

static const struct file_operations hello_fops = {
.owner = THIS_MODULE, /* This is a macro , It's automatically created when the module is compiled __this_module Variable */
.open = hello_open,
.read = hello_read,
.write = hello_write,
};

// Set the initialization entry function
static int __init hello_init(void)
{
register_chrdev(4, MODULE_NAME, &hello_fops);/ The parameters are the main equipment number 、 Equipment name 、 Structure /
return 0;
}

// Set exit function
static void __exit hello_exit(void)
{
unregister_chrdev(4, MODULE_NAME);/ The parameters are the main equipment number 、 Equipment name 、 Structure /
}

// Appoint license edition If not specified
MODULE_LICENSE(“GPL”);
MODULE_AUTHOR(“BGM”);
MODULE_DESCRIPTION(“BGM str driver”);

// The above defined init() and exit() Function is defined as module entry / Exit function
module_init(hello_init);
module_exit(hello_exit);

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Device node generation method ：

Above Demo You need to manually generate device nodes , The generation method is as follows ：

mknod /dev/bgm c 4 0  // among bgm Is the node name  4  Main equipment number 

After generating the device node , We can go through cat /dev/bgm or echo Commands operate on nodes . You can think about it before you operate ,cat and echo What actions will be performed ？

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APP test

After the node is generated , Our usual goal is to provide nodes to user mode programs for operation , Here you can put the following demo Used to control the above character device node , The character device can be read / write / open Wait for the action
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
int main(int argc, char **argv)
{
int fd;
int val = 1;
fd = open(“/dev/bgm”, O_RDWR);// According to your own device name
if (fd < 0)
{
printf(“can’t open!\n”);
}
return 0;
}
Come here , Even if a character device is basically completed , Think about it here , Whether it can automatically generate equipment nodes through code ？ How to achieve ？
Reference resources https://blog.csdn.net/zichuanning520/article/details/123962725 Summarize the practice