Linux设备驱动开发详解-第6章字符设备驱动(二)-支持2个globalmem

1 支持两个globalmem设备的驱动程序

1.1 globalmem_two.c

上一篇中globalmem仅仅作为使用private_data 的范例，直接访问全局变量globalmem_devp会更加结构清晰。如果globalmem不只包括一个设备，而是同时包括两个或两个以上的设备，采用private_data 的优势就会显现出来。

在不对上一篇中代码的globalmem_read()、globalmem_write()、 globalmem_ioctl()等重要函数及 globalmem_fops结构体等数据结构进行任何修改的前提下，只是简单地修改 globalmem_init()、globalmem_exit()和 globalmem_open()，就可以轻松地让globalmem驱动中包含两个同样的设备（次设备号分别为0和1） ，如下代码所示：

/*======================================================================
A globalmem driver as an example of char device drivers
There are two same globalmems in this driver
This example is to introduce the function of file->private_data

The initial developer of the original code is Baohua Song
<author@linuxdriver.cn>. All Rights Reserved.
======================================================================*/
#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>

#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 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*/
struct globalmem_dev *dev;

dev = container_of(inode->i_cdev,struct globalmem_dev,cdev);
filp->private_data = dev;
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:
memset(dev->mem, 0, GLOBALMEM_SIZE);
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;

/*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);
}

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;

/*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);
}

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;
}

/*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,
.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, 2, "globalmem");
else  /* 动态申请设备号 */
{
result = alloc_chrdev_region(&devno, 0, 2, "globalmem");
globalmem_major = MAJOR(devno);
}
if (result < 0)
return result;

/* 动态申请2个设备结构体的内存*/
globalmem_devp = kmalloc(2*sizeof(struct globalmem_dev), GFP_KERNEL);
if (!globalmem_devp)    /*申请失败*/
{
result =  - ENOMEM;
goto fail_malloc;
}
memset(globalmem_devp, 0, 2*sizeof(struct globalmem_dev));

globalmem_setup_cdev(&globalmem_devp[0], 0);
globalmem_setup_cdev(&globalmem_devp[1], 1);
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[0].cdev));
cdev_del(&(globalmem_devp[1].cdev));   /*注销cdev*/
kfree(globalmem_devp);     /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(globalmem_major, 0), 2); /*释放设备号*/
}

MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);

container_of()的作用是通过结构体成员的指针找到对应结构体的指针，这个技巧在 Linux 内核编程中十分常用。在container_of（inode->i_cdev,structglobalmem_dev,cdev）语句中，传给container_of()的第1个参数是结构体成员的指针，第2 个参数为整个结构体的类型，第3 个参数为传入的第1 个参数即结构体成员的类型，container_of()返回值为整个结构体的指针。

2 测试应用程序

//gmen_two_test.c
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>

#define MEM_CLEAR 0x1  /*清0全局内存*/
int main(int argc, char **argv)
{
int fd0 = 0;
int fd1 = 0;

int ret = 0;
int length = 0;
char buffer[1024];

fd0 = open("/dev/globalmem_two0",O_RDWR);	//以读写的方式打开
if(fd0<0)
{
printf("Can not open /dev/leds\n");
close(fd0);
return 0;
}

//写入字符
memset(buffer, 0, 1024);
strcpy(buffer,"test globalmem\n");
length = strlen(buffer);
printf("0 写入的字符length = %d, %s", length, buffer);
ret = lseek(fd0, 0, SEEK_SET);	//定位为相对文件开头0处
ret = write(fd0, buffer, length);

//读取字符
memset(buffer, 0, 1024);
ret = lseek(fd0, 0, SEEK_SET);	//定位为相对文件开头0处
ret = read(fd0, buffer, length);
if(ret>0)
{
printf("0 清除内存前读出的字符length = %d, %s", ret, buffer);
}

//清除字符
memset(buffer, 0, 1024);
ret = lseek(fd0, 0, SEEK_SET);	//定位为相对文件开头0处
ret = ioctl(fd0, MEM_CLEAR, 0);
ret = read(fd0, buffer, length);
if(ret>0)
{
printf("0 清除内存后读出的字符length = %d, %s", ret, buffer);
}

close(fd0);

//
fd1 = open("/dev/globalmem_two1",O_RDWR);	//以读写的方式打开
if(fd1<0)
{
printf("Can not open /dev/leds\n");
close(fd1);
return 0;
}

//写入字符
memset(buffer, 0, 1024);
strcpy(buffer,"test globalmem\n");
length = strlen(buffer);
printf("\n\n1 写入的字符length = %d, %s", length, buffer);
ret = lseek(fd1, 0, SEEK_SET);	//定位为相对文件开头0处
ret = write(fd1, buffer, length);

//读取字符
memset(buffer, 0, 1024);
ret = lseek(fd1, 0, SEEK_SET);	//定位为相对文件开头0处
ret = read(fd1, buffer, length);
if(ret>0)
{
printf("1 清除内存前读出的字符length = %d, %s", ret, buffer);
}

//清除字符
memset(buffer, 0, 1024);
ret = lseek(fd1, 0, SEEK_SET);	//定位为相对文件开头0处
ret = ioctl(fd1, MEM_CLEAR, 0);
ret = read(fd1, buffer, length);
if(ret>0)
{
printf("1 清除内存后读出的字符length = %d, %s", ret, buffer);
}

close(fd1);

return 0;
}

3 globalmem驱动在用户空间的验证

3.1 编译加载globalmem驱动

[root@localhostglobalmem_two]# make

[root@localhostglobalmem_two]# insmod globalmem_two.ko

3.2 globalmem驱动设备节点

[root@localhostglobalmem_two]# mknod /dev/globalmem_two0 c 247 0

[root@localhostglobalmem_two]# mknod /dev/globalmem_two1 c 247 1

3.3 编译执行测试应用程序

[root@localhostglobalmem_two]# gcc -o gmen_two_test gmen_two_test.c

[root@localhostglobalmem_two]# ./gmen_two_test

0 写入的字符length = 15, test globalmem

0 清除内存前读出的字符length = 15, test globalmem

0 清除内存后读出的字符length = 15,

1 写入的字符length = 15, test globalmem

1 清除内存前读出的字符length = 15, test globalmem

1 清除内存后读出的字符length = 15, [root@localhost globalmem_two]#

4 扩展

源码地址：点击打开链接

5 参考文献

[1] 宋宝华.Linux设备驱动开发详解