Kernel APIs:
class_device_create Sample Codes:
MMemory.c
/* Necessary includes for device drivers */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/device.h> /* class_creatre */
#include <linux/cdev.h> /* cdev_init */
//---------------------------------------------------------------------------
#define DEVICE_NAME "memory"
MODULE_LICENSE("Dual BSD/GPL");
/* Declaration of memory.c functions */
int __init memory_init(void);
void __exit memory_exit(void);
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos);
/* Structure that declares the usual file */
/* access functions */
struct file_operations memory_fops = {
.read = memory_read,
.write = memory_write,
.open = memory_open,
.release = memory_release
};
/* Global variables of the driver */
/* Buffer to store data */
char *memory_buffer;
struct class *memory_class = 0;
/*static*/ dev_t dev_num;
struct cdev cdev;
//---------------------------------------------------------------------------
int __init memory_init(void)
{
int result;
/* Registering device */
result = alloc_chrdev_region(&dev_num, 0, 0, DEVICE_NAME);
if (result < 0) {
printk( KERN_ALERT "memory: cannot register device\n");
return result;
}
/* Allocating memory for the buffer */
memory_buffer = kmalloc(1, GFP_KERNEL);
if (!memory_buffer) {
result = -ENOMEM;
goto fail;
}
memset(memory_buffer, 0, 1);
/* populate sysfs entry */
memory_class = class_create(THIS_MODULE, DEVICE_NAME);
/*connect the file operations with the cdev */
cdev_init(&cdev, &memory_fops);
cdev.owner = THIS_MODULE;
/* connect the major/minor number to the cdev */
if (cdev_add(&cdev, dev_num, 1)) {
printk(KERN_ALERT "Bad cdev\n");
return 1;
}
/* seend uevents to udev, so it'll create the /dev node*/
class_device_create(memory_class, NULL, dev_num, NULL, "memory%d", 1);
printk(KERN_ALERT "Inserting memory module\n");
return 0;
fail:
memory_exit();
return result;
}
//---------------------------------------------------------------------------
void __exit memory_exit(void)
{
/* remove the cdev*/
cdev_del(&cdev);
/* Freeing the major number */
unregister_chrdev_region(dev_num, 1);
class_device_destroy(memory_class, dev_num);
class_destroy(memory_class);
/* Freeing buffer memory */
if (memory_buffer) {
kfree(memory_buffer);
}
printk(KERN_ALERT "Removing memory module\n");
}
//---------------------------------------------------------------------------
int memory_open(struct inode *inode, struct file *filp)
{
/* Success */
return 0;
}
//---------------------------------------------------------------------------
int memory_release(struct inode *inode, struct file *filp)
{
/* Success */
return 0;
}
//---------------------------------------------------------------------------
ssize_t memory_read(struct file *filp, char *buf,
size_t count, loff_t *f_pos)
{
/* Transfering data to user space */
copy_to_user(buf,memory_buffer,1);
/* Changing reading position as best suits */
if (*f_pos == 0) {
*f_pos+=1;
return 1;
}
else {
return 0;
}
}
//---------------------------------------------------------------------------
ssize_t memory_write( struct file *filp, const char *buf,
size_t count, loff_t *f_pos)
{
const char *tmp;
tmp = buf + count - 1;
copy_from_user(memory_buffer, tmp, 1);
return 1;
}
//---------------------------------------------------------------------------
/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);
Makefile
obj-m := memory.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KDIR) M=$(PWD) clean
