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

#

#endif

 

#ifndef MEMDEV_NR_DEVS

#

#endif

 

#ifndef MEMDEV_SIZE

#

#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" );

      ;

}

 

/*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 );

 

   /* 静态申请设备号*/

    result , "memdev" );

   if (result
< )

     return result;

 

   /*初始化cdev结构*/

  cdev_init( & cdev,
& mem_fops);

 

   /* 注册字符设备 */

  cdev_add( ), 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, ), );
/*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
-;

    }

}

 

 

 

 

 

 

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。