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/* https://cirosantilli.com/linux-kernel-module-cheat#debugfs */

#include <linux/debugfs.h>

#include <linux/kernel.h>

#include <linux/module.h>

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

static struct dentry *dir, *toplevel_file;

static u32 value = 42;

/* This basically re-implents the write operation of debugfs_create_u32,

* it is just an excuse to illustrate a fop. */

static ssize_t write(struct file *filp, const char __user *buf, size_t len, loff_t *off)

{

int ret;

unsigned long long res;

/* https://stackoverflow.com/questions/6139493/how-convert-char-to-int-in-linux-kernel */

ret = kstrtoull_from_user(buf, len, 10, &res);

if (ret) {

/* Negative error code. */

return ret;

} else {

value = res;

*off= len;

return len;

}

}

static const struct file_operations fops = {

.owner = THIS_MODULE,

.write = write,

};

static int myinit(void)

{

struct dentry *file;

dir = debugfs_create_dir("lkmc_debugfs", 0);

if (!dir) {

pr_alert("debugfs_create_dir failed");

return -1;

}

file = debugfs_create_u32("myfile", S_IRUSR | S_IWUSR, dir, &value);

if (!file) {

pr_alert("debugfs_create_u32 failed");

return -1;

}

/* Created on the toplevel of the debugfs mount,

* and with explicit fops instead of a fixed integer value.

*/

toplevel_file = debugfs_create_file(

"lkmc_debugfs_file", S_IWUSR, NULL, NULL, &fops);

if (!toplevel_file) {

return -1;

}

return 0;

}

static void myexit(void)

{

debugfs_remove_recursive(dir);

debugfs_remove(toplevel_file);

}

module_init(myinit)

module_exit(myexit)

MODULE_LICENSE("GPL");