LDD-LinuxDeviceDrivers/study/debug/debugfs/my_debug/my_debugfs.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/debugfs.h> /* this is for DebugFS libraries */
#include <linux/fs.h>

// http://opensourceforu.com/2010/10/debugging-linux-kernel-with-debugfs/
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Surya Prabhakar <surya_prabhakar@dell.com>");
MODULE_DESCRIPTION("sample code for DebugFS functionality");

#define len 200

u64                 intvalue,hexvalue;
struct dentry       *dirret,*fileret,*u64int,*u64hex;
char                ker_buf[len];
int                 filevalue;


/* read file operation */
static ssize_t myreader(struct file *fp,
                        char __user *user_buffer,
                        size_t count,
                        loff_t *position)
{
     return simple_read_from_buffer(user_buffer, count, position, ker_buf, len);
}

/* write file operation */
static ssize_t mywriter(struct file *fp, const char __user *user_buffer,
                                size_t count, loff_t *position)
{
        if(count > len)
                return -EINVAL;

        return simple_write_to_buffer(ker_buf, len, position, user_buffer, count);
}

static const struct file_operations fops_debug = {
        .read = myreader,
        .write = mywriter,
};

static int __init init_debug(void)
{
    /* create a directory by the name dell in /sys/kernel/debugfs */
    dirret = debugfs_create_dir("gatieme_mydebug", NULL);

    /* create a file in the above directory
    This requires read and write file operations */
    fileret = debugfs_create_file("text", 0644, dirret, &filevalue, &fops_debug);

    /* create a file which takes in a int(64) value */
    u64int = debugfs_create_u64("number", 0644, dirret, &intvalue);
    if (!u64int) {
        printk("error creating int file");
        return (-ENODEV);
    }
    /* takes a hex decimal value */
    u64hex = debugfs_create_x64("hexnum", 0644, dirret, &hexvalue );
    if (!u64hex) {
        printk("error creating hex file");
        return (-ENODEV);
    }

    return (0);
}
module_init(init_debug);

static void __exit exit_debug(void)
{
    /* removing the directory recursively which
    in turn cleans all the file */
    debugfs_remove_recursive(dirret);
}
module_exit(exit_debug);