Linux设备驱动——简单的字符驱动

本文介绍Linux字符设备的静态注册方法，

其中涉及到的模块加载，不了解的可以先参考

构建和运行模块

1. 还是线上源代码：

//memdev.h
# ifndef _MEMDEV_H_
# define _MEMDEV_H_
 
# ifndef MEMDEV_MAJOR
# define MEMDEV_MAJOR 200
# endif
 
# ifndef MEMDEV_NR_DEVS
# define MEMDEV_NR_DEVS 2
# endif
 
# ifndef MEMDEV_SIZE
# define MEMDEV_SIZE 4096
# endif
 
struct mem_dev{
     char * data;
     unsigned long size;
 
};
 
# endif

 

//memdev.c  
# 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 / wait.h >
# include < linux / completion.h >
 
# include "memdev.h"
 
MODULE_LICENSE( "Dual BSD/GPL" );
 
static int   mem_major = MEMDEV_MAJOR;
 
struct mem_dev * mem_devp; /*设备结构体指针*/
 
struct cdev cdev;
 
/*文件打开函数*/
int mem_open( struct inode * inode, struct file * filp)
{
printk( "open own file\n" );
      return 0 ;
}
 
/*文件操作结构体*/
static const struct file_operations mem_fops =
{
  .owner = THIS_MODULE,
  .open = mem_open,
};
 
/*设备驱动模块加载函数*/
static int memdev_init( void )
{
    int result;
    int i;
 
  dev_t devno = MKDEV(mem_major, 0 );
 
    /* 静态申请设备号*/
    result = register_chrdev_region(devno, 2 , "memdev" );
    if (result < 0 )
      return result;
 
    /*初始化cdev结构*/
  cdev_init( & cdev, & mem_fops);
 
    /* 注册字符设备 */
  cdev_add( & cdev, MKDEV(mem_major, 0 ), MEMDEV_NR_DEVS);
 
    return result;
}
 
/*模块卸载函数*/
static void memdev_exit( void )
{
  cdev_del( & cdev);     /*注销设备*/
  unregister_chrdev_region(MKDEV(mem_major, 0 ), 2 ); /*释放设备号*/
}
 
module_init(memdev_init);
module_exit(memdev_exit);

 

#Makefile
ifneq ($(KERNELRELEASE),)
    obj -m : = memdev.o
else
    KERNELDIR ? = /lib /modules /$(shell uname -r) /build
    PWD = $(shell pwd)
default :
    $(MAKE) -C $(KERNELDIR) M =$(PWD) modules
clean :
    rm memdev.mod *  module * memdev.o memdev.ko Module. *
endif
 

 

2. 测试

    首先先make下，生成memdev.ko

    然后insmod memdev.ko生成memdev模块

    创建设备节点：sudo mknod /dev/memdev_t c 200 0

    接下开使用设备文件

    下面是一个测试程序

   // memusr.c
# include <stdio.h >
# include <string.h >
 
int main()
{
    FILE *fp0;
     /*打开设备文件*/
    fp0 = fopen( "/dev/memdev_t", "r+");
     if (fp0 == NULL) {
        printf( "Open Memdev0 Error!\n");
         return - 1;
    }
}
 
 
 
 
 
 

编译运行，然后使用dmesg可以看到日志文件里输出

[38439.741816] Hello World!

[38657.654345] Goodbye

[40393.039520] open own file

 

记得要使用sudo 运行memusr   否则会显示设备打开失败。

 

转载于:https://www.cnblogs.com/Windeal/p/4284680.html