Simple Misc Driver Example

Makefile

# Simple Makefile to build a simple misc driver
# Nick Glynn <Nick.Glynn@feabhas.com>
#

obj-m += misc_example.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

CC := $(CROSS_COMPILE)gcc

all:
        $(MAKE) -C $(KDIR) M=${shell pwd} modules
        
clean:
        -$(MAKE) -C $(KDIR) M=${shell pwd} clean || true
        -rm *.o *.ko *.mod.{c,o} modules.order Module.symvers || true

misc_sample.c

#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/module.h>

static int sample_open(struct inode *inode, struct file *file)
{
    pr_info("I have been awoken\n");
    return 0;
}

static int sample_close(struct inode *inodep, struct file *filp)
{
    pr_info("Sleepy time\n");
    return 0;
}

static ssize_t sample_write(struct file *file, const char __user *buf,
		       size_t len, loff_t *ppos)
{
    pr_info("Yummy - I just ate %d bytes\n", len);
    return len; /* But we don't actually do anything with the data */
}

static const struct file_operations sample_fops = {
    .owner			= THIS_MODULE,
    .write			= sample_write,
    .open			= sample_open,
    .release		= sample_close,
    .llseek 		= no_llseek,
};

struct miscdevice sample_device = {
    .minor = MISC_DYNAMIC_MINOR,
    .name = "simple_misc",
    .fops = &sample_fops,
};

static int __init misc_init(void)
{
    int error;

    error = misc_register(&sample_device);
    if (error) {
        pr_err("can't misc_register :(\n");
        return error;
    }

    pr_info("I'm in\n");
    return 0;
}

static void __exit misc_exit(void)
{
    misc_deregister(&sample_device);
    pr_info("I'm out\n");
}

module_init(misc_init)
module_exit(misc_exit)

MODULE_DESCRIPTION("Simple Misc Driver");
MODULE_AUTHOR("Nick Glynn <n.s.glynn@gmail.com>");
MODULE_LICENSE("GPL");