linux驱动5--一个非常简单的字符设备

1. ldd3上的scull太难了，俺一个新手怎么能看得懂呢？没办法，自己写一个非常非常简单的字符设备。

#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/cdev.h>

dev_t scull_dev_num;
struct cdev* p_scull_dev;

static int scull_open(struct inode* node, struct file *filp)
{
    printk(KERN_ALERT "scull open!\n");
    return 0;
}

static ssize_t scull_read(struct file* filp, char __user *buf, size_t count, loff_t *f_pos)
{
    printk(KERN_ALERT "scull read!\n");
    return 0;
}

static ssize_t scull_write(struct file* filp, const char __user *buf, size_t count, loff_t *f_pos)
{
    printk(KERN_ALERT "scull write!\n");
    return 0;
}

static int scull_release(struct inode *node, struct file* filp)
{
    printk(KERN_ALERT "scull release!\n");
    return 0;
}

static const struct file_operations scull_fops =
{
    .owner = THIS_MODULE,
    .open = scull_open,
    .read = scull_read,
    .write = scull_write,
    .release = scull_release,
};

static int __init scull_init(void)
{
    int ret;
    printk(KERN_ALERT "in scull driver\n");
    //动态分配一个设备号，从0开始分配一个从设备号
    ret = alloc_chrdev_region(&scull_dev_num, 0, 1, "scull");
    if(ret < 0)
    {
        printk(KERN_ALERT "alloc_chrdev_region error!\n");
    }

    //字符设备注册
    p_scull_dev = cdev_alloc();
    p_scull_dev->owner = THIS_MODULE;
    p_scull_dev->ops = &scull_fops;
    cdev_add(p_scull_dev, scull_dev_num, 1);

    return 0;
}

static void __exit scull_exit(void)
{
    printk(KERN_ALERT "goodbye scull dirver\n");
    unregister_chrdev_region(scull_dev_num, 1);
    cdev_del(p_scull_dev);
    return ;
}

MODULE_LICENSE("GPL");

module_init(scull_init);
module_exit(scull_exit);

2. Makefile

ARCH=x86
ifeq ($(ARCH), x86)
    CROSS_COMPILE=
    KDIR = /lib/modules/$(shell uname -r)/build
else
    CROSS_COMPILE= /opt/EmbedSky/4.3.3/bin/arm-none-linux-gnueabi-
    KDIR =/root/kernel/linux-2.6.30.4
endif
PWD = $(shell pwd)

obj-m := scull.o
all:
    make -C $(KDIR) SUBDIRS=$(PWD) modules
clean:
    rm -f *.ko *.o *.mod.o *.mod.c .*.cmd *.symvers *.order

3. test程序

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main ( int argc, char *argv[] )
{
    int fd;
    fd = open("/dev/scull", O_RDWR);
    if(fd < 0)
    {
        perror("open");
    }
    return EXIT_SUCCESS;
}

4. 测试

4.1 创建设备文件

     root@ubuntu:~/driver/2scull# cat /proc/devices | grep "scull" 

     250 scull

     root@ubuntu:~/driver/2scull# mknod /dev/scull c 250 0  //动态分配的主设备号250

     root@ubuntu:~/driver/2scull/test# ll /dev/scull

     crw-r--r-- 1 root root 250, 0 2012-08-28 15:19 /dev/scull

4.2  运行测试程序

     root@ubuntu:~/driver/2scull/test# ./scull_test

     root@ubuntu:~/driver# dmesg 

     [ 2110.894651] in scull driver

     [ 2114.160516] scull open!

     [ 2114.160679] scull release!

 2scull.zip   (下载后改名为: 2scull.tar.gz)