字符设备驱动框架

scull from 《Linux设备驱动程序》

memdev.c

/*
 * memdev.c
 * create at 2015/01/07
 * 字符设备驱动程序框架
 */
#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/slab.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/uaccess.h>

#include "memdev.h"

static mem_major = MEMDEV_MAJOR;

module_param(mem_major, int, S_IRUGO);

/* 设备结构体指针 */
struct mem_dev *mem_devp;

struct cdev cdev;

/* 文件打开函数 */
int mem_open(struct inode *inode, struct file *filp)
{
    struct mem_dev *dev;

    /* 获取次设备号 */
    int num = MINOR(inode->i_rdev);

    if (num > MEMDEV_NR_DEVS)
    return -ENODEV;
    dev = &mem_devp[num];

    filp->private_data = dev;

    return 0;
}

/* 文件释放函数 */
int mem_release(struct inode *inode, struct file *filp)
{
    return 0;
}

/* 读函数 */
static ssize_t mem_read(struct file *filp, char __user *buf, size size, loff_t *ppos)
{
    unsigned long p = *ppos;
    unsigned int count = size;
    int ret = 0;
    struct mem_dev *dev = filp->private_data;

    /* 判断读位置是否有效 */
    if (p >= MEMDEV_SIZE)
    return 0;
    if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

    /*读数据到用户空间*/
    if (copy_to_user(buf, (void*)(dev->data + p), count))
    {
    ret = - EFAULT;
    }
    else
    {
    *ppos += count;
    ret = count;

    printk(KERN_INFO "read %u bytes(s) from %lu\n", count, p);
    }

    return ret;
}

/*写函数*/
static ssize_t mem_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 mem_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 >= MEMDEV_SIZE)
    return 0;
    if (count > MEMDEV_SIZE - p)
    count = MEMDEV_SIZE - p;

    /*从用户空间写入数据*/
    if (copy_from_user(dev->data + p, buf, count))
    ret = - EFAULT;
    else
    {
    *ppos += count;
    ret = count;

    printk(KERN_INFO "written %u bytes(s) from %lu\n", count, p);
    }

    return ret;
}

/* seek文件定位函数 */
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{
    loff_t newpos;

    switch(whence) {
    case 0: /* SEEK_SET */
        newpos = offset;
        break;

    case 1: /* SEEK_CUR */
        newpos = filp->f_pos + offset;
        break;

    case 2: /* SEEK_END */
        newpos = MEMDEV_SIZE -1 + offset;
        break;

    default: /* can‘t happen */
        return -EINVAL;
    }
    if ((newpos<0) || (newpos>MEMDEV_SIZE))
    return -EINVAL;

    filp->f_pos = newpos;
    return newpos;
}

/*文件操作结构体*/
static const struct file_operations mem_fops =
{
    .owner   = THIS_MODULE,
    .llseek  = mem_llseek,
    .read    = mem_read,
    .write   = mem_write,
    .open    = mem_open,
    .release = mem_release,
};

/*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*/
    if (mem_major)
    result = register_chrdev_region(devno, 2, "memdev");
    else /* 动态分配设备号 */
    {
    result = alloc_chrdev_region(&devno, 0, 2, "memdev");
    mem_major = MAJOR(devno);
    }

    if (result < 0)
    return result;

    /*初始化cdev结构*/
    cdev_init(&cdev, &mem_fops);
    cdev.owner = THIS_MODULE;
    cdev.ops = &mem_fops;

    /* 注册字符设备 */
    cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);

    /* 为设备描述结构分配内存*/
    mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
    if (!mem_devp) /*申请失败*/
    {
    result = - ENOMEM;
    goto fail_malloc;
    }
    memset(mem_devp, 0, sizeof(struct mem_dev));

    /*为设备分配内存*/
    for (i=0; i < MEMDEV_NR_DEVS; i++)
    {
        mem_devp[i].size = MEMDEV_SIZE;
        mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
        memset(mem_devp[i].data, 0, MEMDEV_SIZE);
    }

    return 0;

fail_malloc:
    unregister_chrdev_region(devno, 1);

    return result;
}

/*模块卸载函数*/
static void memdev_exit(void)
{
    cdev_del(&cdev); /*注销设备*/
    kfree(mem_devp); /*释放设备结构体内存*/
    unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
}

MODULE_AUTHOR("Elvalad");
MODULE_LICENSE("GPL");

module_init(memdev_init);
module_exit(memdev_exit);

memdev.h

/*
 * memdev.h
 * create at 2015/01/07
 */

#ifndef _MEMDEV_H_
#define _MEMDEV_H_

#ifndef MEMDEV_MAJOR
#define MEMDEV_MAJOR 260 /*预设的mem的主设备号*/
#endif

#ifndef MEMDEV_NR_DEVS
#define MEMDEV_NR_DEVS 2 /*设备数*/
#endif

#ifndef MEMDEV_SIZE
#define MEMDEV_SIZE 4096
#endif

/*mem设备描述结构体*/
struct mem_dev
{
  char *data;
  unsigned long size;
};

#endif /* _MEMDEV_H_ */

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 -rf *.o *.mod.c *.mod.o *.ko
endif

memdevtest.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <linux/i2c.h>
#include <linux/fcntl.h>

int main()
{
    int fd;
    //写入memdev设备的内容
    char buf[]="it‘s funny!!!";
    //memdev设备的内容读入到该buf中
    char buf_read[4096]; 

    if((fd=open("/dev/memdev",O_RDWR))==-1) //打开memdev设备
    printf("open memdev ERROR\n");
    else
    printf("open memdev SUCCESS!\n");

    printf("buf is %s\n",buf);
    write(fd,buf,sizeof(buf)); //把buf中的内容写入memdev设备
    lseek(fd,0,SEEK_SET); //把文件指针重新定位到文件开始的位置
    read(fd,buf_read,sizeof(buf)); //把memdev设备中的内容读入到buf_read中
    printf("buf_read is %s\n",buf_read);

    return 0;
}

编译字符驱动之后会产生一个memdev.ko文件，然后执行

sudo insmod memdev.ko
lsmod 或者 cat /proc/devices 查看ko是否插入

创建设备节点

sudo mknod memdev c 260 0

编译memdevtest.c程序测试这个字符设备驱动

gcc -o memdevtest memdevtest.c

执行此测试程序，因为设备文件建立在/dev目录下，在执行此程序时因为要打开设备文件，所以需要root权限下执行。