1. 准备

首先在 menuconfig 时开启 debugfs
Kernel hacking --->
Generic Kernel Debugging Instruments --->
[*] Debug Filesystem
Debugfs default access (Access normal) --->

挂载debugfs

yangxr@vexpress:/ # cat /etc/fstab
proc           /proc      proc    defaults   0     0
tmpfs          /tmp       tmpfs   defaults   0     0
sysfs          /sys       sysfs   defaults   0     0
var            /dev       tmpfs   defaults   0     0
ramfs          /dev       tmpfs   defaults   0     0
debugfs        /debug     debugfs defaults   0     0

2. 示例

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>

static struct dentry *hello_dentry;
static u32 hello_u32;
static u16 hello_u16;
static u32 hello_arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9};

static struct debugfs_u32_array arr_info = {
        .array = hello_arr,
        .n_elements = 9,
};

static struct debugfs_blob_wrapper mem_info;

#define HELLO_MAX_SIZE 32
static char hello_buf[HELLO_MAX_SIZE];

static ssize_t hello_read (struct file *filp, char __user *to,
                size_t count, loff_t *ppos)
{
        return simple_read_from_buffer(to, count, ppos, hello_buf, HELLO_MAX_SIZE);
}

static ssize_t hello_write (struct file *filp, const char __user *from,
                size_t count, loff_t *ppos)
{
        if (*ppos == HELLO_MAX_SIZE)
                return count;
        return simple_write_to_buffer(hello_buf, HELLO_MAX_SIZE, ppos,
                from, count);
}

static struct file_operations hello_fops = {
        .owner = THIS_MODULE,
        .read = hello_read,
        .write = hello_write,
};

static int __init hello_init(void)
{
        if ((hello_dentry = debugfs_create_dir("hello", NULL)) == NULL) {
                printk("Create /debug/hello failed !\n");
                return -1;
        }
        printk("Create /debug/hello succeed !\n");

        // 创建u32节点，使用 10进制显示
        debugfs_create_u32("u32", 0666, hello_dentry, &hello_u32);
        // 创建u16节点，使用 16进制显示
        debugfs_create_x16("u16", 0666, hello_dentry, &hello_u16);
        // 创建u32数组 (只读)
        debugfs_create_u32_array("u32_arr", 0666, hello_dentry, &arr_info);

        // 显示一片内存 (只读)
        mem_info.data = (void *)hello_arr;
        mem_info.size = sizeof(hello_arr);
        debugfs_create_blob("mem", 0666, hello_dentry, &mem_info);

        if (debugfs_create_file("hello_fops", 0666,
                                hello_dentry, hello_buf, &hello_fops) == NULL) {
                printk("Create /debug/hello_fops failed\n");
                return -1;
        }

        return 0;
}

static void __exit hello_exit(void)
{
        if (hello_dentry) {
                // 递归删除/debug/hello
                debugfs_remove_recursive(hello_dentry);
                printk("Remove /debug/hello succeed !\n");
        }
}

module_init(hello_init);
module_exit(hello_exit);

MODULE_LICENSE("GPL");