分配内存

//scullc.c
//#include <linux/config.h>
#include <linux/sched.h>
#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/proc_fs.h>
#include <linux/fcntl.h>    /* O_ACCMODE */
#include <linux/seq_file.h>
#include <linux/cdev.h>
#include <linux/slab.h>

#include <asm/system.h>        /* cli(), *_flags */
#include <asm/uaccess.h>    /* copy_*_user */
#include "scullc.h"


/*
 * 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);

MODULE_AUTHOR("Alessandro Rubini, Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
struct kmem_cache *scull_cache;
struct scull_dev *scull_devices;    /* allocated in scull_init_module */

//kmem_cache_t *scull_cache;
//kmem_cache *scull_cache;

/*
 * The proc filesystem: function to read and entry
 */

int scull_read_procmem(char *buf, char **start, off_t offset,
                   int count, int *eof, void *data)
{
    int i, j, len = 0;
    int limit = count - 80; /* Don‘t print more than this */

    for (i = 0; i < scull_nr_devs && len <= limit; i++) {
        struct scull_dev *d = &scull_devices[i];
        struct scull_qset *qs = d->data;
        if (down_interruptible(&d->sem))
            return -ERESTARTSYS;
        len += sprintf(buf+len,"\nDevice %i: qset %i, q %i, sz %li\n",
                i, d->qset, d->quantum, d->size);
        for (; qs && len <= limit; qs = qs->next) { /* scan the list */
            len += sprintf(buf + len, "  item at %p, qset at %p\n",
                    qs, qs->data);
            if (qs->data && !qs->next) /* dump only the last item */
                for (j = 0; j < d->qset; j++) {
                    if (qs->data[j])
                        len += sprintf(buf + len,
                                "    % 4i: %8p\n",
                                j, qs->data[j]);
                }
        }
        up(&scull_devices[i].sem);
    }
    *eof = 1;
    return len;
}


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;
}


/*
 * Data management: read and write
 */

/*
 * 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;
    }
    */
    
    if (!dptr->data[s_pos]){
        dptr->data[s_pos] = kmem_cache_alloc(scull_cache,GFP_KERNEL);
        if (!dptr->data[s_pos])
            goto out;
        memset(dptr->data[s_pos],0,scull_quantum);    
    }
    
    /* 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;
}


/*
 * The "extended" operations -- only seek
 */

loff_t scull_llseek(struct file *filp, loff_t off, int whence)
{
    struct scull_dev *dev = filp->private_data;
    loff_t newpos;

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

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

      case 2: /* SEEK_END */
        newpos = dev->size + off;
        break;

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


/*
 * The ioctl() implementation
 */

int scull_ioctl(struct inode *inode, struct file *filp,
                 unsigned int cmd, unsigned long arg)
{

    int err = 0, tmp;
    int retval = 0;
    
    /*
     * extract the type and number bitfields, and don‘t decode
     * wrong cmds: return ENOTTY (inappropriate ioctl) before access_ok()
     */
    if (_IOC_TYPE(cmd) != SCULL_IOC_MAGIC) return -ENOTTY;
    if (_IOC_NR(cmd) > SCULL_IOC_MAXNR) return -ENOTTY;

    /*
     * the direction is a bitmask, and VERIFY_WRITE catches R/W
     * transfers. `Type‘ is user-oriented, while
     * access_ok is kernel-oriented, so the concept of "read" and
     * "write" is reversed
     */
    if (_IOC_DIR(cmd) & _IOC_READ) /*through access_ok() check the addr is legal userspace address */
        err = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
    else if (_IOC_DIR(cmd) & _IOC_WRITE)
        err =  !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
    if (err) return -EFAULT;

    switch(cmd) {

      case SCULL_IOCRESET:
        scull_quantum = SCULL_QUANTUM;
        scull_qset = SCULL_QSET;
        break;
        
      case SCULL_IOCSQUANTUM: /* Set: arg points to the value */
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        retval = __get_user(scull_quantum, (int __user *)arg);
        break;

      case SCULL_IOCTQUANTUM: /* Tell: arg is the value */
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        scull_quantum = arg;
        break;

      case SCULL_IOCGQUANTUM: /* Get: arg is pointer to result */
        retval = __put_user(scull_quantum, (int __user *)arg);
        break;

      case SCULL_IOCQQUANTUM: /* Query: return it (it‘s positive) */
        return scull_quantum;

      case SCULL_IOCXQUANTUM: /* eXchange: use arg as pointer */
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        tmp = scull_quantum;
        retval = __get_user(scull_quantum, (int __user *)arg);
        if (retval == 0)
            retval = __put_user(tmp, (int __user *)arg);
        break;

      case SCULL_IOCHQUANTUM: /* sHift: like Tell + Query */
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        tmp = scull_quantum;
        scull_quantum = arg;
        return tmp;
        
      case SCULL_IOCSQSET:
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        retval = __get_user(scull_qset, (int __user *)arg);
        break;

      case SCULL_IOCTQSET:
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        scull_qset = arg;
        break;

      case SCULL_IOCGQSET:
        retval = __put_user(scull_qset, (int __user *)arg);
        break;

      case SCULL_IOCQQSET:
        return scull_qset;

      case SCULL_IOCXQSET:
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        tmp = scull_qset;
        retval = __get_user(scull_qset, (int __user *)arg);
        if (retval == 0)
            retval = put_user(tmp, (int __user *)arg);
        break;

      case SCULL_IOCHQSET:
        if (! capable (CAP_SYS_ADMIN))
            return -EPERM;
        tmp = scull_qset;
        scull_qset = arg;
        return tmp;

        /*
         * The following two change the buffer size for scullpipe.
         * The scullpipe device uses this same ioctl method, just to
         * write less code. Actually, it‘s the same driver, isn‘t it?
         */
/*
      case SCULL_P_IOCTSIZE:
        scull_p_buffer = arg;
        break;

      case SCULL_P_IOCQSIZE:
        return scull_p_buffer;
*/

      default:  /* redundant, as cmd was checked against MAXNR */
        return -ENOTTY;
    }
    return retval;

}



struct file_operations scull_fops = { //The function of system call should obtain the semaphore to protect the sharing the resource
    .owner =    THIS_MODULE,      
    .llseek =   scull_llseek,
    .read =     scull_read,
    .write =    scull_write,
    .ioctl =    scull_ioctl,
    .open =     scull_open,
    .release =  scull_release,
};



/*
 * 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);
    }
    if (scull_cache)
        kmem_cache_destroy(scull_cache);
#ifdef SCULL_DEBUG /* use proc only if debugging */
    scull_remove_proc();
#endif
    remove_proc_entry("scullmem", NULL /* parent dir */);

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

    /* and call the cleanup functions for friend devices */


}

/*
 * 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);
    
    cdev_init(&dev->cdev, &scull_fops);
    dev->cdev.owner = THIS_MODULE;
    dev->cdev.ops = &scull_fops;
    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.
 */
    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
     */
    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);    //The semaphore should be initialise before the scull device could be used 
        scull_setup_cdev(&scull_devices[i], i);
    }

        /* At this point call the init function for any friend device */
    dev = MKDEV(scull_major, scull_minor + scull_nr_devs);
/*debug*/
    create_proc_read_entry("scullmem", 0 /* default mode */,
            NULL /* parent dir */, scull_read_procmem,
            NULL /* client data */);

    scull_cache = kmem_cache_create("scullc",scull_quantum,
                    0,SLAB_HWCACHE_ALIGN,NULL);
    if (!scull_cache) {
        scull_cleanup_module();
        return -ENOMEM;    
    }
    return 0; /* succeed */

  fail:
    scull_cleanup_module();
    return result;
}

module_init(scull_init_module);
module_exit(scull_cleanup_module);

//scull.h
#ifndef _SCULL_H_
#define _SCULL_H_

#include <linux/ioctl.h> /* needed for the _IOW etc stuff used later */





#ifndef SCULL_MAJOR
#define SCULL_MAJOR 0   /* dynamic major by default */
#endif

#ifndef SCULL_NR_DEVS
#define SCULL_NR_DEVS 4    /* scull0 through scull3 */
#endif



/*
 * The bare device is a variable-length region of memory.
 * Use a linked list of indirect blocks.
 *
 * "scull_dev->data" points to an array of pointers, each
 * pointer refers to a memory area of SCULL_QUANTUM bytes.
 *
 * The array (quantum-set) is SCULL_QSET long.
 */
#ifndef SCULL_QUANTUM
#define SCULL_QUANTUM 4000
#endif

#ifndef SCULL_QSET
#define SCULL_QSET    1000
#endif


/*
 * Representation of scull quantum sets.
 */
struct scull_qset {
    void **data;
    struct scull_qset *next;
};

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



/*
 * The different configurable parameters
 */
extern int scull_major;     /* main.c */
extern int scull_nr_devs;
extern int scull_quantum;
extern int scull_qset;




/*
 * Prototypes for shared functions
 */


int     scull_access_init(dev_t dev);
void    scull_access_cleanup(void);

int     scull_trim(struct scull_dev *dev);

ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
                   loff_t *f_pos);
ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
                    loff_t *f_pos);
loff_t  scull_llseek(struct file *filp, loff_t off, int whence);
int     scull_ioctl(struct inode *inode, struct file *filp,
                    unsigned int cmd, unsigned long arg);


/*
 * Ioctl definitions
 */

/* Use ‘k‘ as magic number */
#define SCULL_IOC_MAGIC  ‘k‘
/* Please use a different 8-bit number in your code */

#define SCULL_IOCRESET    _IO(SCULL_IOC_MAGIC, 0)

/*
 * S means "Set" through a ptr,
 * T means "Tell" directly with the argument value
 * G means "Get": reply by setting through a pointer
 * Q means "Query": response is on the return value
 * X means "eXchange": switch G and S atomically
 * H means "sHift": switch T and Q atomically
 */
#define SCULL_IOCSQUANTUM _IOW(SCULL_IOC_MAGIC,  1, int)
#define SCULL_IOCSQSET    _IOW(SCULL_IOC_MAGIC,  2, int)
#define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC,   3)
#define SCULL_IOCTQSET    _IO(SCULL_IOC_MAGIC,   4)
#define SCULL_IOCGQUANTUM _IOR(SCULL_IOC_MAGIC,  5, int)
#define SCULL_IOCGQSET    _IOR(SCULL_IOC_MAGIC,  6, int)
#define SCULL_IOCQQUANTUM _IO(SCULL_IOC_MAGIC,   7)
#define SCULL_IOCQQSET    _IO(SCULL_IOC_MAGIC,   8)
#define SCULL_IOCXQUANTUM _IOWR(SCULL_IOC_MAGIC, 9, int)
#define SCULL_IOCXQSET    _IOWR(SCULL_IOC_MAGIC,10, int)
#define SCULL_IOCHQUANTUM _IO(SCULL_IOC_MAGIC,  11)
#define SCULL_IOCHQSET    _IO(SCULL_IOC_MAGIC,  12)

/*
 * The other entities only have "Tell" and "Query", because they‘re
 * not printed in the book, and there‘s no need to have all six.
 * (The previous stuff was only there to show different ways to do it.
 */
#define SCULL_P_IOCTSIZE _IO(SCULL_IOC_MAGIC,   13)
#define SCULL_P_IOCQSIZE _IO(SCULL_IOC_MAGIC,   14)
/* ... more to come */

#define SCULL_IOC_MAXNR 14

#endif /* _SCULL_H_ */

//test.c
#include <stdio.h>
#include <sys/types.h> 
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h> //_exit
#include <stdlib.h> // exit
int main(int argc,char **argv)
{
    int fd,size;
    char s[] = "Hello World";
    char buffer[80] = {"\0"};
    if((fd = open("/dev/scull0",O_RDWR)) < 0 ){
        printf("errno = %d\n",errno);
        exit(0);
    }
    size = write(fd,s,sizeof(s));
    printf("write in %d bytes\n",size);
    close(fd);
    fd = open("/dev/scull0",O_RDWR);
    size = read(fd,buffer,sizeof(buffer));
    printf("read out %d bytes\n",size);
    printf("%s\n",buffer);
    sleep(100);
    close(fd);
    return 0;

}