char drivers

scull : 只是一段开辟的内存，我们把他当作设备，来为之开发驱动

流程：

1.  注册主设备号
2.  开辟内存， 将内核中注册的设备信息和他的相关操作进行绑定

3. 对相关操作进行编码

4. 退出对数据进行清空。

数据结构：

dev_t : 整形， 设备编号
file_operations  :结构体,对文件的一些操作，里面的元素大多是函数指针
例如：
struct file_operations scull_fops = {
    .owner =    THIS_MODULE,
    .read =     scull_read,
    .write =    scull_write,
    .open =     scull_open,
    .release =  scull_release,
};
file : 结构体，内核中文件的信息，重要的包括mode_t f_mode（文件模式，读写） loff_t f_pos : 当前的读/写位置，private_date (保存任何信息)

inode : 结构体 重要的包括 dev_t i_rdev 设备编号  struct cdev *i_cdev 设备在内核中的结构

cdev : 结构体 设备在内核中的结构，内核有封装好的初始化函数

scull 特有的数据结构

struct scull_dev {
    struct cdev cdev;      /* Char device structure        */

    struct scull_qset *data;  /* Pointer to first quantum set */
    int quantum;              /* the current quantum size */
    int qset;                 /* the current array size */
    unsigned long size;       /* amount of data stored here */
    unsigned int access_key;  /* used by sculluid and scullpriv */
    struct semaphore sem;     /* mutual exclusion semaphore     */
};
类似于实现一个父类是struct cdev的子类。

内存开辟的方式：
struct scull_qset {
    void **data;
    struct scull_qset *next;
};
单链表，每个节点是一个量子集，每个量子集里由多个量子组成

读写方式：每次仅对一个量子进行读写，完成最底层的组件。

测试方法： 在/dev 中 用mknod创建节点，然后对其进行读写
 cat /proc/devices | grep scull  
找到 scull 的main 设备号

mknod /dev/scull c 250 0

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>

#include <linux/kernel.h>    /* printk() */
#include <linux/slab.h>        /* kmalloc() */
#include <linux/fs.h>        /* everything... */
#include <linux/errno.h>    /* error codes */
#include <linux/types.h>    /* size_t */
#include <linux/fcntl.h>    /* O_ACCMODE */
#include <linux/cdev.h>
#include <asm/system.h>        /* cli(), *_flags */
#include <asm/uaccess.h>    /* copy_*_user */
#include "scull.h"        /* local definitions */

/*
 * Our parameters which can be set at load time.
 */
int scull_major = SCULL_MAJOR;
int scull_minor = 0;
int scull_nr_devs = SCULL_NR_DEVS;    /* number of bare scull devices */
int scull_quantum = SCULL_QUANTUM;
int scull_qset = SCULL_QSET;

module_param(scull_major, int, S_IRUGO);
module_param(scull_minor, int, S_IRUGO);
module_param(scull_nr_devs, int, S_IRUGO);
module_param(scull_quantum, int, S_IRUGO);
module_param(scull_qset, int, S_IRUGO);

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

/*
 * Empty out the scull device; must be called with the device
 * semaphore held.
 */
int scull_trim(struct scull_dev *dev)
{
    struct scull_qset *next, *dptr;
    int qset = dev->qset; /* "dev" is not-null */
    int i;

    for (dptr = dev->data; dptr; dptr = next) { /* all the list items */
        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 information */

    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) {
        if (down_interruptible(&dev->sem))
            return -ERESTARTSYS;
        scull_trim(dev); /* ignore errors */
        up(&dev->sem);
    }
    return 0; /* success */
}

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;
}

/*
 * Data management: 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;    /* the first listitem */
    int quantum = dev->quantum, qset = dev->qset;
    int itemsize = quantum * qset; /* how many bytes in the listitem */
    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;

    /* 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 (defined elsewhere) */
    dptr = scull_follow(dev, item);

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

    /* read only up to the end of this quantum */
    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;
}

int scull_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
    int err = 0;
    int retval;
    
    if(_IOC_TYPE(cmd) != SCULL_IOC_MAGIC )
        return -ENOTTY;

    if(_IOC_NR(cmd) > SCULL_IOC_MAXNR )
        return -ENOTTY;

    if(_IOC_DIR(cmd) & _IOC_READ)
    {
        err = !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
    }

    if(_IOC_DIR(cmd) & _IOC_WRITE)
    {
        err = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
    }
    if(err)
    {
        return -EFAULT;
    }

    printk("correct command \n");
    
    switch(cmd)
    {
        case SCULL_IOCGQUANTUM:
            printk("IOCGQUANTUM\n");
            retval = __put_user(scull_quantum, (int __user*)arg);
            break;
        case SCULL_IOCSQUANTUM:
            retval = __get_user(scull_quantum, (int __user*)arg);
            break;
    }
}

struct file_operations scull_fops = {
    .owner = THIS_MODULE,
    .read = scull_read,
    .write = scull_write,
    .open = scull_open,
    .release = scull_release,
    .ioctl = scull_ioctl,
};

/*
 * Finally, the module stuff
 */

/*
 * The cleanup function is used to handle initialization failures as well.
 * Thefore, it must be careful to work correctly even if some of the items
 * have not been initialized
 */
void scull_cleanup_module(void)
{
    int i;
    dev_t devno = MKDEV(scull_major, scull_minor);

    /* Get rid of our char dev entries */
    if (scull_devices) {
        for (i = 0; i < scull_nr_devs; i++) {
            scull_trim(scull_devices + i);
            cdev_del(&scull_devices[i].cdev);
        }
        kfree(scull_devices);
    }

    /* cleanup_module is never called if registering failed */
    unregister_chrdev_region(devno, scull_nr_devs);
}


/*
 * Set up the char_dev structure for this device.
 */
static void scull_setup_cdev(struct scull_dev *dev, int index)
{
    int err, devno = MKDEV(scull_major, scull_minor + index);
    

// 初始化设备
    cdev_init(&dev->cdev, &scull_fops);
    dev->cdev.owner = THIS_MODULE;
//    dev->cdev.ops = &scull_fops;



// 激活设备  链接到内核


    err = cdev_add (&dev->cdev, devno, 1);
    /* Fail gracefully if need be */
    if (err)
        printk(KERN_NOTICE "Error %d adding scull%d", err, index);
}


int scull_init_module(void)
{
    int result, i;
    dev_t dev = 0;

/*
 * Get a range of minor numbers to work with, asking for a dynamic
 * major unless directed otherwise at load time.
 */

// 得到 设备号
     printk("%x\n", SCULL_IOCGQUANTUM);
    if (scull_major) {
        dev = MKDEV(scull_major, scull_minor);
        result = register_chrdev_region(dev, scull_nr_devs, "scull");
    } else {
        result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs,
                "scull");
        scull_major = MAJOR(dev);
    }
    if (result < 0) {
        printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
        return result;
    }

     /*
     * allocate the devices -- we can't have them static, as the number
     * can be specified at load time
     */

//  开辟空间


    scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);
    
    if (!scull_devices) {
        result = -ENOMEM;
        goto fail; /* Make this more graceful */
    }
    
    memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));

        /* 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);
        scull_setup_cdev(&scull_devices[i], i);
    }
    printk("succeed install scrull dev\n");
    return 0; /* succeed */

  fail:
    scull_cleanup_module();
    return result;
}



module_init(scull_init_module);
module_exit(scull_cleanup_module);

MODULE_AUTHOR("Tekkamanninja");
MODULE_LICENSE("Dual BSD/GPL");