Linux设备驱动学习(1) 全局内存空间“设备”驱动程序globalmem

分手后的思念是犯贱 2022-06-13 06:48 203阅读 0赞

此“设备”是一个在内存中恒久的空间，在模块初始化时便已分配。

使用modinfo查看编译出来的模块信息

$modinfo ./globalmem.ko

将自定义的主设备号作为参数插入到模块中，使用

$sudo insmod ./globalmem.ko globalmem\_major=xxx

来分配。

/*======================================================================
        A globalmem driver as an example of char device drivers  
       
        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>
    #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 200    /*预设的globalmem的主设备号*/
    
    
    static int 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*/
      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:
          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;             //这里的p是*ppos的一份拷贝，表示已经读取了的字节数目
      unsigned int count = size;		//需要读取的字节数
      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)//GLOBALMEM_SIZE - p 表示还剩下的可读字节数
        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                                //假设分配了0x1~0x9共9个字节的空间，读之前p=5表示已读了5个字节，count=5表示需要读6个字节，在函数中count被置9-5=4，因为只能读剩下的4个字节。
      {                                   //读完之后，*ppos = 5 + 4 ，下次再读就返回0了。写和读类似。。。
        *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)//index为次设备号
    {
      int err, devno = MKDEV(globalmem_major, index);//得到总设备号
    
    
      cdev_init(&dev->cdev, &globalmem_fops);//将字符设备和对设备操作的函数相关联
      dev->cdev.owner = THIS_MODULE;
      dev->cdev.ops = &globalmem_fops;
      err = cdev_add(&dev->cdev, devno, 1);//将字符设备和内核相关联
      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); /*初始化并注册cdev*/
      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("Song Baohua");
    MODULE_LICENSE("Dual BSD/GPL");
    
    
    module_param(globalmem_major, int, S_IRUGO);
    
    
    module_init(globalmem_init);
    module_exit(globalmem_exit);

与设备号相关的宏位于

/usr/src/linux-headers-2.6.35-22/include/linux/kdev\_t.h

总设备号，主设备号，次设备号
      1 #ifndef _LINUX_KDEV_T_H
      2 #define _LINUX_KDEV_T_H
      3 #ifdef __KERNEL__					//若已定义__KERNEL__符号则MAJOR
      4 #define MINORBITS       20
      5 #define MINORMASK       ((1U << MINORBITS) - 1)
      6 
      7 #define MAJOR(dev)      ((unsigned int) ((dev) >> MINORBITS))//左移20位得到高12为作为主设备号
      8 #define MINOR(dev)      ((unsigned int) ((dev) & MINORMASK))//MINORMASK为20个1（二进制），取低20位作为次设备号
      9 #define MKDEV(ma,mi)    (((ma) << MINORBITS) | (mi))	//将ma放在高12位，mi放在低20位
    
    
     90 #else /* __KERNEL__ *///未定义__KERNEL__符号
     91 
     92 /*
     93 Some programs want their definitions of MAJOR and MINOR and MKDEV
     94 from the kernel sources. These must be the externally visible ones.
     95 */
     96 #define MAJOR(dev)      ((dev)>>8)			//这里就是左移8位
     97 #define MINOR(dev)      ((dev) & 0xff)		//取低8位作为次设备号
     98 #define MKDEV(ma,mi)    ((ma)<<8 | (mi))		//ma左移8位并上mi
     99 #endif /* __KERNEL__ */
    100 #endif

Makefile如下，稍微加了一点改进

OBJ     = globalmem
    obj-m += $(OBJ).o
    MAJOR   = 200 
    MINOR   = 0
    #generate the path
    CURRENT_PATH:=$(shell pwd)
    #the current kernel version number
    LINUX_KERNEL:=$(shell uname -r)
    #the absolute path
    LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)
    #complie object
    all:
            make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules
    
    install:
            sudo insmod ./$(OBJ).ko
            sudo mknod /dev/my_$(OBJ) c $(MAJOR) $(MINOR)
    
    uninstall:
            sudo rmmod $(OBJ)
            sudo rm -rf /dev/my_$(OBJ)
    #clean
    clean:
            make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean

可以使用命令来测试设备

\#ls > /dev/my\_globalmem

\#cat /dev/my\_globalmem

或者用测试程序

这里的程序是从设备中读取数据，测试之前要先向设备中写入数据。

\#cat file > /dev/my\_globalmem

/*main.c*/
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <string.h>
     
     
    int main(void)
    {
            int testdev;
            int i,rf=0;
            char buf[100];
     
            memset(buf, 0, sizeof(buf));
            testdev = open("/dev/my_globalmem",O_RDWR); //open the device 
            if ( testdev == -1 )
            {   
            perror("open\n");
            exit(0);
            }   
            for(i=0;i<10;i++)
            {   
                    rf=read(testdev,buf,100);               //read some bytes from the device and put the data to buf
                    if(rf<0)
                    perror("read error\n");
                    printf("times %d ,Read:\n%s", i, buf);
                    printf("\ntimes %d ,Read finish\n", i); 
            }   
            close(testdev);                         //close the device 
            return 0;

这是有两个globalmem“设备”的驱动程序，只需要更改设备初始化函数和卸载函数

/*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");//申请使用两个总设备号
      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);//从设备号为0
      globalmem_setup_cdev(&globalmem_devp[1], 1);//从设备号为1
      return 0;
    
      fail_malloc: unregister_chrdev_region(devno, 2);
      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*/
    }

我们可以看到以上程序是没有加锁的，在对设备的read，write，ioctl操作中会产生竞态，多个进程同时访问的话，驱动极易崩溃。