NeuSoft(4)编写字符设备驱动

1、要求：实现简单的字符设备驱动程序

2、源码清单

#include <linux/module.h>

#include <linux/types.h>

#include <linux/fs.h>

#include <linux/errno.h>

#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/init.h>

#include <linux/cdev.h>

#include <asm/io.h>

#include <asm/system.h>

#include <asm/uaccess.h>

#include <linux/slab.h>

#define GLOBALMEM_SIZE 0x1000 /*全局内存最大4K字节*/

#define MEM_CLEAR 0x1 /*清0全局内存*/

#define GLOBALMEM_MAJOR 254 /*预设的globalmem的主设备号*/

static globalmem_major = GLOBALMEM_MAJOR;

/*globalmem设备结构体*/

struct globalmem_dev

{

struct cdev cdev; /*cdev结构体*/

unsigned char mem[GLOBALMEM_SIZE]; /*全局内存*/

struct semaphore sem; /*并发控制用的信号量*/

};

struct globalmem_dev *globalmem_devp; /*设备结构体指针*/

/*文件打开函数*/

int globalmem_open(struct inode *inode, struct file *filp)

{

/*将设备结构体指针赋值给文件私有数据指针*/

filp->private_data = globalmem_devp;

return 0;

}

/*文件释放函数*/

int globalmem_release(struct inode *inode, struct file *filp)

{

return 0;

}

/* ioctl设备控制函数 */

static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned int cmd, unsigned long arg)

{

struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/

switch (cmd)

{

case MEM_CLEAR:

if (down_interruptible(&dev->sem))

{

return - ERESTARTSYS;

}

memset(dev->mem, 0, GLOBALMEM_SIZE);

up(&dev->sem); //释放信号量

printk(KERN_INFO "globalmem is set to zero\n");

break;

default:

return - EINVAL;

}

return 0;

}

/*读函数*/

static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)

{

unsigned long p = *ppos;

unsigned int count = size;

int ret = 0;

struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/

/*分析和获取有效的写长度*/

if (p >= GLOBALMEM_SIZE)

return count ? - ENXIO: 0;

if (count > GLOBALMEM_SIZE - p)

count = GLOBALMEM_SIZE - p;

if (down_interruptible(&dev->sem))

{

return - ERESTARTSYS;

}

/*内核空间->用户空间*/

if (copy_to_user(buf, (void*)(dev->mem + p), count))

{

ret = - EFAULT;

}

else

{

*ppos += count;

ret = count;

printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);

}

up(&dev->sem); //释放信号量

return ret;

}

/*写函数*/

static ssize_t globalmem_write(struct file *filp, const char __user *buf,

size_t size, loff_t *ppos)

{

unsigned long p = *ppos;

unsigned int count = size;

int ret = 0;

struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/

/*分析和获取有效的写长度*/

if (p >= GLOBALMEM_SIZE)

return count ? - ENXIO: 0;

if (count > GLOBALMEM_SIZE - p)

count = GLOBALMEM_SIZE - p;

if (down_interruptible(&dev->sem))//获得信号量

{

return - ERESTARTSYS;

}

/*用户空间->内核空间*/

if (copy_from_user(dev->mem + p, buf, count))

ret = - EFAULT;

else

{

*ppos += count;

ret = count;

printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);

}

up(&dev->sem); //释放信号量

return ret;

}

/* seek文件定位函数 */

static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig)

{

loff_t ret = 0;

switch (orig)

{

case 0: /*相对文件开始位置偏移*/

if (offset < 0)

{

ret = - EINVAL;

break;

}

if ((unsigned int)offset > GLOBALMEM_SIZE)

{

ret = - EINVAL;

break;

}

filp->f_pos = (unsigned int)offset;

ret = filp->f_pos;

break;

case 1: /*相对文件当前位置偏移*/

if ((filp->f_pos + offset) > GLOBALMEM_SIZE)

{

ret = - EINVAL;

break;

}

if ((filp->f_pos + offset) < 0)

{

ret = - EINVAL;

break;

}

filp->f_pos += offset;

ret = filp->f_pos;

break;

default:

ret = - EINVAL;

break;

}

return ret;

}

/* http://blog.csdn.net/zhou1232006/article/details/6867584*/

/*文件操作结构体*/

static const struct file_operations globalmem_fops =

{

.owner = THIS_MODULE,

.llseek = globalmem_llseek,

.read = globalmem_read,

.write = globalmem_write,

//.compat_ioctl = globalmem_ioctl,

.unlocked_ioctl = globalmem_ioctl,

.open = globalmem_open,

.release = globalmem_release,

};

/*初始化并注册cdev*/

static void globalmem_setup_cdev(struct globalmem_dev *dev, int index)

{

int err, devno = MKDEV(globalmem_major, index);

cdev_init(&dev->cdev, &globalmem_fops);

dev->cdev.owner = THIS_MODULE;

dev->cdev.ops = &globalmem_fops;

err = cdev_add(&dev->cdev, devno, 1);

if (err)

printk(KERN_NOTICE "Error %d adding LED%d", err, index);

}

/*设备驱动模块加载函数*/

int globalmem_init(void)

{

int result;

dev_t devno = MKDEV(globalmem_major, 0);

/* 申请设备号*/

/*if (globalmem_major)

result = register_chrdev_region(devno, 1, "globalmem");

else /* 动态申请设备号 */

{*/

result = alloc_chrdev_region(&devno, 0, 1, "globalmem");

globalmem_major = MAJOR(devno);

//}

if (result < 0)

return result;

/* 动态申请设备结构体的内存*/

globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);

if (!globalmem_devp) /*申请失败*/

{

result = - ENOMEM;

goto fail_malloc;

}

memset(globalmem_devp, 0, sizeof(struct globalmem_dev));

globalmem_setup_cdev(globalmem_devp, 0);

sema_init(&globalmem_devp->sem,1); /*初始化信号量*/

return 0;

fail_malloc: unregister_chrdev_region(devno, 1);

return result;

}

/*模块卸载函数*/

void globalmem_exit(void)

{

cdev_del(&globalmem_devp->cdev); /*注销cdev*/

kfree(globalmem_devp); /*释放设备结构体内存*/

unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); /*释放设备号*/

}

MODULE_AUTHOR("Zhao guohui");

MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);

module_exit(globalmem_exit);

3、编译用Makefile

obj-m := globalmem.o

KERNELBUILD :=/usr/src/linux-headers-3.2.0-23-generic-pae

default:

make -C $(KERNELBUILD) M=$(shell pwd) modules

clean:

rm -rf *.o *.ko *.mod.c

1）error: unknown field ‘ioctl’ specified in initializer

这是由于跨版本移植的时候由于内核提供的函数变化而引起的错误：

解决：http://blog.csdn.net/zhou1232006/article/details/6867584

2）error:implicit declaration of function ‘kmalloc’ [-Werror=implicit-function-declaration]

解决：http://blog.csdn.net/liukun321/article/details/6785608

3）error: ‘globalfifo_devp’ undeclared (first use in this function)

参考：http://www.tuicool.com/articles/6r2M3a

error: implicit declaration of function ‘init_MUTEX’ [-Werror=implicit-function-declaration]

4、验证

首先加载内核模块insmod gllobalmem.ko

设备忙的解决方法

让程序一直寻找可以使用的设备号。

终端输入 cat /proc/devices

找到globalmem的设备号

建立设备文件：mknod /dev/globalmem c 你找到的设备号 0

[root@localhost driver_study]# echo 'hello world' > /dev/globalmem

[root@localhost driver_study]# cat /dev/globalmem

hello world