The sample code of Song Baohua's detailed explanation of Linux device driver development: Basic Character Device Driver

Simplest character device driver code

Scull. c

#include <linux/fs.h>#include <linux/kernel.h>#include <linux/cdev.h>#include <linux/module.h>#include <linux/slab.h>#include <linux/gfp.h>#include <asm/uaccess.h>#defineSCULL_MAJOR252#define SCULL_NAME"scull"#define MAX_DATA0x1000staticint scull_major = SCULL_MAJOR;struct scull_dev {struct cdev cdev;char data[MAX_DATA];struct semaphore sem;};MODULE_LICENSE("Dual BSD/GPL");MODULE_AUTHOR("BG2BKK");structscull_dev *scull_devp;intscull_open(struct inode *inode, struct file *filp){struct scull_dev *dev = container_of(inode->i_cdev, struct scull_dev, cdev);filp->private_data = dev;printk(KERN_ALERT "open the scull device\n");return 0;}intscull_release(struct inode *inode, struct file *filp){printk(KERN_ALERT "close the scull device\n");return 0;}ssize_tscull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_ops){struct scull_dev *dev = filp->private_data;unsigned longp = *f_ops;unsigned intcnt = count;int ret = 0;if(down_interruptible(&dev->sem))return -ERESTARTSYS;if(copy_to_user(buf, dev->data,cnt)){ret = -EFAULT;} else {*f_ops += cnt;ret = cnt;printk(KERN_ALERT "read %u bytes from %lu\n",cnt, p);}up(&dev->sem);printk(KERN_ALERT "read %d bytes\n",count);return ret;}ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_ops){struct scull_dev *dev = filp->private_data;unsigned long p = *f_ops;unsigned int cnt = count;int ret = 0;if(down_interruptible(&dev->sem))return -ERESTARTSYS;if(copy_from_user(dev->data,buf, cnt))ret = -EFAULT;else {*f_ops += cnt;ret = cnt;printk(KERN_ALERT "written %u bytes from %lu\n",cnt, p);}up(&dev->sem);printk(KERN_ALERT "write %d bytes\n",count);return ret;}structfile_operations scull_fops = {.owner=THIS_MODULE,.open=scull_open,.release=scull_release,.write=scull_write,.read=scull_read,};staticvoidscull_setup_cdev(struct scull_dev *dev, int index){int err, devno = MKDEV(scull_major, index);cdev_init(&dev->cdev, &scull_fops);dev->cdev.owner = THIS_MODULE;err = cdev_add(&dev->cdev, devno, 1);if(err)printk(KERN_NOTICE "ERROR %d adding scull_dev %d", err, index);}intscull_init(void){int result;dev_tdevno = MKDEV(scull_major,0);if(scull_major)result = register_chrdev_region(devno, 1, "scull");else {result = alloc_chrdev_region(&devno, 0, 1, "scull");scull_major = MAJOR(devno);}if(result < 0)return result;scull_devp = kmalloc(sizeof(struct scull_dev), GFP_KERNEL);if(!scull_devp){result = -ENOMEM;goto fail_malloc;}memset(scull_devp, 0 , sizeof(struct scull_dev));scull_setup_cdev(scull_devp, 0);init_MUTEX(&scull_devp->sem);printk(KERN_ALERT "init scull device\n");return 0;fail_malloc:unregister_chrdev_region(devno, 1);return result;}voidscull_cleanup(void){cdev_del(&scull_devp->cdev);kfree(scull_devp);unregister_chrdev_region(MKDEV(scull_major, 0), 1);printk(KERN_ALERT "clean scull device\n");}module_init(scull_init);module_exit(scull_cleanup);

Test code

/************************************************************************* *fileName:    test.c *description: test the myscull.c *author:      Hzc *create time: 2007-04-20 *modify info: -*************************************************************************/#include <stdio.h>#include <fcntl.h>#include <sys/ioctl.h>#include <sys/types.h>/* device path */char path[] = "/dev/scull";char buf[10];char rbuf[10];int i;int t = 1;intmain (){  int f = open (path, O_RDWR);   for (i = 0; i < 10; i++)    {      buf[i] = i;      printf("buf[%d] = %d\n",i,buf[i]);    }printf("write %d bytes\n",write (f, buf, 10));//  close (f);//////  f = open (path, O_RDONLY);// if (f == -1)//    {//      printf ("device open error 2!\n");//      return 1;//    }  printf ("Read the string from device...\n");printf("read %d bytes\n",read (f, rbuf, 10));  for (i = 0; i < 10; i++)    {      printf ("%d\n", rbuf[i]);    }  close (f);}

Makefile

#KERNEL_DIR := /home/huang/linux-2.6.18/KERNEL_DIR := /lib/modules/$(shell uname -r)/buildPWD:= $(shell pwd)obj-m := scull.odefault:$(MAKE) -C $(KERNEL_DIR) M=$(PWD) modulestest: test.cgcc $< -o $@.o  -gclean:rm -rf *.o *.ko *~ *.order *.symvers *.markers *.mod.c

Test script

1 load_scull.sh

#!/bin/sh/sbin/insmod scull.komknod /dev/scull c 252 0

2 unload_scull.sh

#!/bin/sh/sbin/rmmod scull.korm /dev/scull -f

3 test. Sh

#!/bin/shmake cleanmake make testsudo ./unload_scullsudo ./load_scullsudo ./test.o