scull—字符设备之总结

1.scull character driver program
/*
 * Filename:scull.c
 * Function:the character test driver
 * Author:dengwei
 * Time:2010-4-20
 */
#include
#include
#include

#include     /*size_t, dev_t*/
#include       /* register_chrdev_region*/
#include
#include
#include     /* O_ACCMODE */
#include      /*struct cdev*/
#include     /*kfree*/
#include   /*contander_of*/
#include     /* error codes */
#include         /* cli(), *_flags */
#include     /* copy_*_user */

#include"scull.h"

static dev_t dev;
static int scull_major = SCULL_MAJOR;
static int scull_minor = SCULL_MINOR;
static int scull_nr_devs = SCULL_NR_DEVS;
static int scull_quantum = SCULL_QUANTUM;
static int scull_qset = SCULL_QSET;
//static int result = -1;
static char __initdata info[] = "This is the character test driver!\n";
static struct class *scull_class;

static struct scull_dev *scull_devices;  /*allocated in scull_init_module*/

/*
 * Empty out the scull device; must be called with the device
 * semaphore held.scull_dev
 */
int scull_trim(struct scull_dev *dev)
{
    struct scull_qset *next, *dptr;
    int qset = dev->qset; /* "dev  非空" */
    int i;
    for (dptr = dev->data; dptr; dptr = next )
    {
        if (dptr->data){
            for (i = 0; i < qset; i++)
                kfree(dptr->data[i]);
            kfree(dptr->data);
            dptr->data = NULL;
        }
        next = dptr->next;
        kfree(dptr);
    }
    dev->size = 0;
    dev->quantum = scull_quantum;
    dev->qset = scull_qset;
    dev->data = NULL;
    return 0;
}
/*
 * open and close
 */
int scull_open(struct inode *inode, struct file *filp)
{
    struct scull_dev *dev; /*device infomation*/
    dev = container_of(inode->i_cdev, struct scull_dev, cdev);
    filp->private_data = dev;  /*for other methods*/

    /* now trim to 0 the length of the device if open was write_only */
    if ( (filp->f_flags & O_ACCMODE) == O_WRONLY){
        scull_trim(dev);
    }
    return 0;
}

int scull_release(struct inode *inode, struct file *filp)
{
    return 0;
}

/*
 *Follow the list
 */
struct scull_qset *scull_follow(struct scull_dev *dev, int n)
{
    struct scull_qset *qs = dev->data;

        /* Allocate first qset explicitly if need be */
    if (! qs) {
        qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
        if (qs == NULL)
            return NULL;  /* Never mind */
        memset(qs, 0, sizeof(struct scull_qset));
    }

    /* Then follow the list */
    while (n--) {
        if (!qs->next) {
            qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
            if (qs->next == NULL)
                return NULL;  /* Never mind */
            memset(qs->next, 0, sizeof(struct scull_qset));
        }
        qs = qs->next;
        continue;
    }
    return qs;
}



/*
 * read and write
 */
ssize_t scull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
    struct scull_dev *dev = filp->private_data;
    struct scull_qset *dptr; /*第一个链表项*/
    int quantum = dev->quantum, qset = dev->qset;
    int itemsize = quantum * qset;  /* 该链表项有多少字节*/
    int item, s_pos, q_pos, rest;
    ssize_t retval = 0;

    if (down_interruptible(&dev->sem))
        return -ERESTARTSYS;
    if (*f_pos >= dev->size)
        goto  out;
    if (*f_pos + count >= dev->size )
        count = dev->size - *f_pos;

    /*在量子集中寻找链表项目、qset索引以及偏移量*/
    item = (long)*f_pos / itemsize;
    rest = (long)*f_pos % itemsize;
    s_pos = rest / quantum; q_pos = rest % quantum;

    dptr = scull_follow(dev, item);

    if (dptr == NULL || !dptr->data || !dptr->data[s_pos])
        goto  out;  /* don't fill holes*/

    /*  读取该量子的数据直到结尾 */
    if (count > quantum - q_pos)
        count = quantum - q_pos;

    if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)){
        retval = -EFAULT;
        goto out;
    }
    *f_pos += count;
    retval = count;

  out:
    up(&dev->sem);
    return retval;
}

ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
{
    struct scull_dev *dev = filp->private_data;
    struct scull_qset *dptr;
    int quantum = dev->quantum, qset = dev->qset;
    int itemsize = quantum * qset;
    int item, s_pos, q_pos, rest;
    ssize_t retval = -ENOMEM; /* value used in "goto out" statements */

    if (down_interruptible(&dev->sem))
        return -ERESTARTSYS;

    /* find listitem, qset index and offset in the quantum */
    item = (long)*f_pos / itemsize;
    rest = (long)*f_pos % itemsize;
    s_pos = rest / quantum; q_pos = rest % quantum;

    /* follow the list up to the right position */
    dptr = scull_follow(dev, item);
    if (dptr == NULL)
        goto out;
    if (!dptr->data) {
        dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);
        if (!dptr->data)
            goto out;
        memset(dptr->data, 0, qset * sizeof(char *));
    }
    if (!dptr->data[s_pos]) {
        dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);
        if (!dptr->data[s_pos])
            goto out;
    }
    /* write only up to the end of this quantum */
    if (count > quantum - q_pos)
        count = quantum - q_pos;

    if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) {
        retval = -EFAULT;
        goto out;
    }
    *f_pos += count;
    retval = count;

        /* update the size */
    if (dev->size < *f_pos)
        dev->size = *f_pos;

  out:
    up(&dev->sem);
    return retval;
}

/* 关联file_operations */
struct file_operations scull_fops = {
        .owner = THIS_MODULE,
        .read = scull_read,
        .write = scull_write,
        .open = scull_open,
        .release = scull_release
};

static int scull_setup_cdev(struct scull_dev *scull_dev, int index)
{
    int err;
    dev_t devno = MKDEV(scull_major,scull_minor + index);
//    int major = MAJOR(dev), minor = MINOR(dev);
//    dev_t devno = MKDEV(major, minor + index);   /* 利用已经获得的设备号 */

    cdev_init(&scull_dev->cdev, &scull_fops);   /*cdev 的初始化*/
    scull_dev->cdev.owner = THIS_MODULE;
    scull_dev->cdev.ops = &scull_fops;
    err = cdev_add(&scull_dev->cdev, devno, 1);
    if (err)
    {
        printk(KERN_NOTICE "Error %d adding scull!", err);
        return err;
    }
    return 0;
}   /*scull 设备注册*/

static int __init scull_init(void)
{
    int ret = -1;
    int i;
    printk(info);
    /* 动态分配设备号*/
    if (scull_major){
        dev = MKDEV(scull_major,scull_minor );
        ret = register_chrdev_region(dev, scull_nr_devs, "scull");
    }
    else{
        ret = alloc_chrdev_region(&dev, scull_minor,scull_nr_devs,"scull");
        scull_major = MAJOR(dev);
    }
    if (ret < 0){
        printk(KERN_WARNING  "scull: can't get major %d\n",scull_major);
        return ret;
    }
    else{
        printk(DEVICE_NAME "major = %d\n",scull_major);
    }
    //    struct cdev *sdev = cdev_alloc();   /*分配一个独立得cdev结构*/
    scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);
    if (!scull_devices) {
        ret = -ENOMEM;
        return ret;  /* Make this more graceful */
    }
    memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));
    /* void *memset(void *s,int c,size_t n)总的作用：将已开辟内存空间 s 的首 n 个字节的值设为值 c */


    /* Initialize each device. */
    for (i = 0; i < scull_nr_devs; i++) {
        scull_devices[i].quantum = scull_quantum;
        scull_devices[i].qset = scull_qset;
        init_MUTEX(&scull_devices[i].sem);
        ret = scull_setup_cdev(&scull_devices[i], i);
        if (ret < 0){
            printk(DEVICE_NAME "can't register major module!\n");
            return ret;
        }
}
    /*注册一个类，使得mdev能在/dev下创建设备节点？？？？？？*/
    scull_class = class_create(THIS_MODULE,DEVICE_NAME);
    if(IS_ERR(scull_class))
    {
        printk(KERN_ALERT "Err:faile in scull_class!\n");
        return -1;
    }
    /*创建设备节点，名字为DEVICE_NAME ，主设备号用上面动态生成的dev*/
    device_create(scull_class, NULL, dev, NULL, DEVICE_NAME);
    printk(DEVICE_NAME"initializa\n");
    return 0;
}

static void __exit scull_exit(void)
{
       printk(KERN_ALERT "Moudle exit! Charater Device Driver End!\n");
       unregister_chrdev_region(dev,scull_nr_devs);
       device_destroy(scull_class, dev);
       class_destroy(scull_class);
}
module_init(scull_init);
module_exit(scull_exit);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_DESCRIPTION("CHARACTER DEVICE DRVER");
MODULE_AUTHOR("dengwei");
//scull.c
-------------------------------------------------------------------
#define SCULL_MAJOR         0
#define SCULL_MINOR         0
#define SCULL_NR_DEVS         1
#define DEVICE_NAME       "scull"

#define SCULL_QUANTUM  4000
#define SCULL_QSET      1000

/* Representation of scull quantum qset */
struct scull_qset{
    void **data;
    struct scull_qset *next;
};
struct scull_dev{
    struct scull_qset *data;
    int quantum;
    int qset;
    unsigned long size;
    unsigned int access_key;
    struct semaphore sem;
    struct cdev cdev;
};
//scull.h
-------------------------------------------------------------
ifneq    ($(KERNELRELEASE),)
obj-m    :=scull.o

else
KDIR    :=/lib/modules/$(shell uname -r)/build
PWD    := $(shell pwd)

default:
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
clean:
    rm -r -f .tmp_versions *.mod.c .*.cmd *.o  Modules.symvers
endif
//Makefile
=============================================================
2.测试程序
#include
#include
#include
#include
#include
 
int main()
{
    char buffer1[20]={0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};
    char buffer2[20]={0};
    int sculltest;
    int code,i;
     
    sculltest = open("/dev/scull",O_WRONLY );
 
    for ( i=20 ; i>0 ; i-=code)        {  
        if ((code=write(sculltest , &buffer1[20-i] , i)) != i) printf("write error! code=%d \n",code);
        else   printf("write ok! code=%d \n",code);
    }
 
    close(sculltest);
 
 
    sculltest = open("/dev/scull",O_RDONLY );
 
    for ( i=20 ; i>0 ; i-=code)        {  
        if ((code=read(sculltest , &buffer2[20-i] , i)) != i) printf("read error! code=%d \n",code);
        else   printf("read ok! code=%d \n",code);
    }
     
    for(i=0;i<20;i+=5) 
        printf("[%d]=%d [%d]=%d [%d]=%d [%d]=%d [%d]=%d\n",i,buffer2[i],i+1,buffer2[i+1],i+2,buffer2[i+2],i+3,buffer2[i+3],i+4,buffer2[i+4]);
 
    printf("\n"); 
 
    close(sculltest);
  exit(0);
}
//scull-test.c
-------------------------------------------------------------------
#CROSS_COMPILE    =/home/tekkaman/working/crosstool-gcc410-k26222/gcc-4.1.0-glibc-2.3.2/arm-9tdmi-linux-gnu/bin/arm-9tdmi-linux-gnu-
#CC    = $(CROSS_COMPILE)gcc
CC = gcc


all : scull_test.o
        $(CC)  -o scull_test scull_test.o

clean:
        rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions

//Makefile
==============================================================
3,result:
root@dw:/home/dengwei/eclipse_workspace/scull_driver_test# cat /proc/devices |grep sc
 10 misc
251 scull
//驱动挂载
-------------------------------------------------------------
root@dw:/home/dw/scull-test# ./scull_test
write ok! code=20
read ok! code=20
[0]=0 [1]=1 [2]=2 [3]=3 [4]=4
[5]=5 [6]=6 [7]=7 [8]=8 [9]=9
[10]=10 [11]=11 [12]=12 [13]=13 [14]=14
[15]=15 [16]=16 [17]=17 [18]=18 [19]=19
//测试成功
==========================================================
总结：
1，
struct cdev 和dev_t 的联系。
dev_t:包含设备号，用来表示设备；
cdev:设备的结构
怎样把两者联系起来呢？
通过这个函数：
int cdev_add(struct cdev *dev, dev_t num, unsigned int count)
argument *dev:表示要注册的设备结构；
argument num:表示要注册的设备号；//书上说是设备对应的第一个编号？？
argument count:表示应该和该设备关联的设备号的数量。
2，class_create(THIS_MODULE, DEVICE_NAME)
   device_create 
    见下一章（在驱动模块初始化函数中实现设备节点的自动创建）

3,字符设备的执行流程：
获取设备号->注册设备->关联file_operations结构->open->write->read->release资源->close(设备)
=========================================================
参考资料：http://blog.chinaunix.net/u1/34474/showart_404278.html