linux-kernel-module-cheat/kernel_module/debugfs.c

/*
Adapted from: https://github.com/chadversary/debugfs-tutorial/blob/47b3cf7ca47208c61ccb51b27aac6f9f932bfe0b/example1/debugfs_example1.c

Usage:

	/debugfs.sh

Requires `CONFIG_DEBUG_FS=y`.

Only the more basic fops can be implemented in debugfs, e.g. mmap is never called:

- https://patchwork.kernel.org/patch/9252557/
- https://github.com/torvalds/linux/blob/v4.9/fs/debugfs/file.c#L212
*/

#include <linux/debugfs.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <uapi/linux/stat.h> /* S_IRUSR */

static struct dentry *dir;
static u32 value = 42;

static int myinit(void)
{
	struct dentry *file;
	dir = debugfs_create_dir("lkmc_debugfs", 0);
	if (!dir) {
		printk(KERN_ALERT "debugfs_create_dir failed");
		return -1;
	}
	file = debugfs_create_u32("myfile", S_IRUSR, dir, &value);
	if (!file) {
		printk(KERN_ALERT "debugfs_create_u32 failed");
		return -1;
	}
	return 0;
}

static void myexit(void)
{
	debugfs_remove_recursive(dir);
}

module_init(myinit)
module_exit(myexit)
MODULE_LICENSE("GPL");