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字符设备驱动开发

1. 相关头文件与函数

1.1 fs.h

在文件 include/linux/fs.h 中，内核提供了三个函数来注册一组字符设备编号：

• register_chrdev_region()
• alloc_chrdev_region()
• register_chrdev()

（1）register_chrdev_region

int register_chrdev_region(dev_t from, unsigned count, const char *name)

• from：要分配的设备编号范围的初始值，这组连续设备号的起始设备号。
• count：连续编号范围，是这组设备号的大小（也是次设备号的个数）。
• name：编号相关联的设备名称（/proc/devices），本组设备的驱动名称。

（2）alloc_chrdev_region

int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)

• dev：alloc_chrdev_region函数向内核申请下来的设备号。
• baseminor：次设备号的起始。
• count：申请次设备号的个数。
• name：执行 cat /proc/devices 显示的名称。

（3）register_chrdev（老版本的字符设备申请函数）

int register_chrdev(unsigned int major, const char *name, const struct file_operations *fops)

• major：主设备号，当用户设置为0时，内核会动态分配一个设备号。
• name：设备名称。
• fops：文件系统的接口指针。

1.2 kdev_t.h

头文件位置 include/linux/kdev_t.h，定义了以下宏：

#define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS))#define MINOR(dev) ((unsigned int) ((dev) & MINORMASK))#define MKDEV(ma, mi) (((ma) << MINORBITS) | (mi))

• MKDEV：将主设备号和次设备号组合成一个 dev_t 类型的设备编号。
• dev_t 类型是 unsigned int，高12位为主设备号，低20位为次设备号。

1.3 cdev.h

头文件位置 include/linux/cdev.h，定义了 cdev 结构体：

struct cdev {    struct kobject kobj;    struct module *owner;    const struct file_operations *ops;    struct list_head list;    dev_t dev;    unsigned int count;}

• cdev.dev：设备号，高12位为主设备号，低20位为次设备号。

2. 静态申请字符类设备号

2.1 代码示例

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #define DEVICE_NAME "scdev"#define DEVICE_MINOR_NUM 2#define DEV_MAJOR 0#define DEV_MINOR 0MODULE_LICENSE("Dual BSD/GPL");MODULE_AUTHOR("iTOPEET_dz");int numdev_major = DEV_MAJOR;int numdev_minor = DEV_MINOR;module_param(numdev_major, int, S_IRUSR);module_param(numdev_minor, int, S_IRUSR);static int scdev_init(void) { int ret = 0; dev_t num_dev; printk(KERN_EMERG "numdev_major is %d!\n", numdev_major); printk(KERN_EMERG "numdev_minor is %d!\n", numdev_minor); if (numdev_major) { num_dev = MKDEV(numdev_major, numdev_minor); ret = register_chrdev_region(num_dev, DEVICE_MINOR_NUM, DEVICE_NAME); } else { printk(KERN_EMERG "numdev_major %d is failed!\n", numdev_major); } if (ret < 0) { printk(KERN_EMERG "register_chrdev_region req %d is failed!\n", numdev_major); } printk(KERN_EMERG "scdev_init!\n"); return 0;}static void scdev_exit(void) { printk(KERN_EMERG "scdev_exit!\n"); unregister_chrdev_region(MKDEV(numdev_major, numdev_minor), DEVICE_MINOR_NUM);}module_init(scdev_init);module_exit(scdev_exit);
        
       
      
     
    
   

2.2 Makefile

#!/bin/bashobj-m += request_cdev_num.oKDIR := /home/topeet/iTop4412_Kernel_3.0PWD := $(shell pwd)all:    make -C $(KDIR) M=$(PWD) modulesclean:    rm -rf *.mod.c *.o *.order *.ko *.mod.o *.symvers

3. 动态申请字符类设备号

3.1 驱动代码

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #define DEVICE_NAME "acdev"#define DEVICE_MINOR_NUM 2#define DEV_MAJOR 0#define DEV_MINOR 0MODULE_LICENSE("Dual BSD/GPL");MODULE_AUTHOR("iTOPEET_dz");int numdev_major = DEV_MAJOR;int numdev_minor = DEV_MINOR;module_param(numdev_major, int, S_IRUSR);module_param(numdev_minor, int, S_IRUSR);static int acdev_init(void) { int ret = 0; dev_t num_dev; printk(KERN_EMERG "numdev_major is %d!\n", numdev_major); printk(KERN_EMERG "numdev_minor is %d!\n", numdev_minor); if (numdev_major) { num_dev = MKDEV(numdev_major, numdev_minor); ret = register_chrdev_region(num_dev, DEVICE_MINOR_NUM, DEVICE_NAME); } else { ret = alloc_chrdev_region(&num_dev, numdev_minor, DEVICE_MINOR_NUM, DEVICE_NAME); numdev_major = MAJOR(num_dev); printk(KERN_EMERG "adev_region req %d !\n", numdev_major); } if (ret < 0) { printk(KERN_EMERG "register_chrdev_region req %d is failed!\n", numdev_major); } printk(KERN_EMERG "acdev_init!\n"); return 0;}static void acdev_exit(void) { printk(KERN_EMERG "acdev_exit!\n"); unregister_chrdev_region(MKDEV(numdev_major, numdev_minor), DEVICE_MINOR_NUM);}module_init(acdev_init);module_exit(acdev_exit);
        
       
      
     
    
   

3.2 代码调试

[root@iTOP-4412]# insmod request_acdev_num.ko[root@iTOP-4412]# rmmod request_acdev_num

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