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    <[e-mail]>. 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_SIZE0x1000/*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