linux驱动：[3]高级字符设备驱动之ioctl

测试平台： x86 PC linux-4.4.0

1.实验目的：

学习并编写ioctl linux高级字符设备驱动程序。

编写驱动 scull ，使用5个指令实现对设备数据的清零，读取，写入操作。

2.驱动代码：(解析见下方)

scull.c:

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           #include "scull.h"//设备私有数据struct scull_dev { int data; struct cdev cdev;} dev;//最大IOCTL命令号#define SCULL_IOC_MAXNR 4//默认自动分配主设备号#define SCULL_DEV_MAJOR 0static int scull_major = SCULL_DEV_MAJOR;module_param(scull_major, int, S_IRUGO);struct class *scull_class;struct cdev cdev;long scull_ioctl(struct file *filp, unsigned int cmd, unsigned long arg){ int err = 0, retval = 0;//判断命令幻数是否匹配 if (_IOC_TYPE(cmd) != SCULL_IOC_MAGIC) return -ENOTTY;//判断命令序号是否非法 if (_IOC_NR(cmd) > SCULL_IOC_MAXNR) return -ENOTTY;//判断空间是否可访问 /* VERIFY_WRITE 是 VERIFY_READ 超集 */ if (_IOC_DIR(cmd) & _IOC_READ) err = !access_ok(VERIFY_WRITE, (void *)arg, _IOC_SIZE(cmd)); else if (_IOC_DIR(cmd) & _IOC_WRITE) err = !access_ok(VERIFY_READ, (void *)arg, _IOC_SIZE(cmd)); if (err) return -EFAULT; switch (cmd) { case SCULL_IOC_CLEAR://数据清零 dev.data = 0; printk("SCULL_IOC_CLEAR data: 0\n"); break; case SCULL_IOC_GET://获取数据(通过指针) retval = __put_user(dev.data, (int __user *)arg); printk("SCULL_IOC_GET data: %d\n", dev.data); break; case SCULL_IOC_QUERY://获取数据(通过返回值) printk("SCULL_IOC_QUERY data: %d\n", dev.data); retval = dev.data; break; case SCULL_IOC_SET://设置数据(通过指针) retval = __get_user(dev.data, (int __user *)arg); printk("SCULL_IOC_SET data: %d\n", dev.data); break; case SCULL_IOC_TELL://设置数据(通过直接引用参数值) dev.data = arg; printk("SCULL_IOC_TELL data: %d\n", arg); break; default: retval = -EINVAL; break; } return retval;}static const struct file_operations scull_fops = { .owner = THIS_MODULE, .unlocked_ioctl = scull_ioctl,//linux 2.6.36内核之后unlocked_ioctl取代ioctl};static int scull_init(void){ //设备号 dev_t devno = MKDEV(scull_major, 0); int result; if (scull_major)//静态分配设备号 result = register_chrdev_region(devno, 1, "scull"); else { //动态分配设备号 result = alloc_chrdev_region(&devno, 0, 1, "scull"); scull_major = MAJOR(devno); } if (result < 0) return result;//用于udev/mdev自动创建节点 scull_class = class_create(THIS_MODULE, "scull"); device_create(scull_class, NULL, devno, NULL, "scull");//静态添加cdev cdev_init(&cdev, &scull_fops); cdev.owner = THIS_MODULE; cdev_add(&cdev, devno, 1); printk("scull init success\n"); return 0;}static void scull_exit(void){ cdev_del(&cdev); device_destroy(scull_class, MKDEV(scull_major, 0)); class_destroy(scull_class); unregister_chrdev_region(MKDEV(scull_major, 0), 1); printk("scull exit success\n");}MODULE_AUTHOR("Ziping Chen 
           
            ");MODULE_LICENSE("GPL");module_init(scull_init);module_exit(scull_exit);

scull.h:

#ifndef SCULL_H_#define SCULL_H_//定义幻数#define SCULL_IOC_MAGIC '$'//定义命令->//数据清零#define SCULL_IOC_CLEAR _IO(SCULL_IOC_MAGIC, 0)//获取数据(通过指针)#define SCULL_IOC_GET   _IOR(SCULL_IOC_MAGIC, 1, int)//获取数据(通过返回值)#define SCULL_IOC_QUERY _IO(SCULL_IOC_MAGIC, 2)//设置数据(通过指针)#define SCULL_IOC_SET   _IOW(SCULL_IOC_MAGIC, 3, int)//设置数据(通过直接引用参数值)#define SCULL_IOC_TELL  _IO(SCULL_IOC_MAGIC, 4)#endif

Makefile:

obj-m := scull.o #编译进模块KERNELDIR := /lib/modules/4.4.0-59-generic/build #此处为linux内核库目录PWD := $(shell pwd) #获取当前目录OUTPUT := $(obj-m) $(obj-m:.o=.ko) $(obj-m:.o=.mod.o) $(obj-m:.o=.mod.c) modules.order Module.symversmodules:    $(MAKE) -C $(KERNELDIR) M=$(PWD) modulesclean:    rm -rf $(OUTPUT)

linux c应用程序测试：

#include 
   
    #include 
    
     #include 
     
      #include "scull.h"int main(void){    int fd;    int data;//打开设备    fd = open("/dev/scull", O_RDWR);    if (fd == -1) {        printf("open scull device failed!\n");        return -1;    }//数据清零      ioctl(fd, SCULL_IOC_CLEAR);//直接传值测试    data = ioctl(fd, SCULL_IOC_QUERY);    printf("app data %d\n", data);    data = 100;    ioctl(fd, SCULL_IOC_TELL, data);//指针传值测试    ioctl(fd, SCULL_IOC_GET, &data);    data = 122;    ioctl(fd, SCULL_IOC_SET, &data);    return 0;}

测试结果：

result

3.代码解析：

代码的大部分解析都位于上面测试，这里我只是提一下程序编写过程中可能出现的问题：

error: unknown field 'ioctl' specified in initializer

这个错误是因为在linux 2.6.36内核之后，去掉了原来的ioctl，添加两个新的成员：

long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);

将scull_fops中.ioctl替换为.unlocked_ioctl，另外scull_ioctl()要去掉inode参数，返回类型为long。