scull内存驱动（3）

billycatcat

               
               
                /*
* main.c -- the bare scull char module
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files.  The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates.   No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
*/
/*#include */
#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 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;    /*全局主设备号，为了动态分配，初始化为SCULL_MAJOR*/
int scull_minor =   0;            /*全局次设备号*/
int scull_nr_devs = SCULL_NR_DEVS;    /*全局的设备个数*/
int scull_quantum = SCULL_QUANTUM;    /*全局量子数目*/
int scull_qset =    SCULL_QSET;        /*全局量子集数目*/
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);
/*模块参数声明，允许在insmod或modprobe装载模块时对参数进行赋值*/
MODULE_AUTHOR("Alessandro Rubini, Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
struct scull_dev *scull_devices;    /* 指向设备结构的全局指针，在scull_init_module中才分配空间 */
/*
* Empty out the scull device; must be called with the device
* semaphore held.
   释放整个数据区，并且以写入方式打开时由scull_open调用，在模块清除函数中也会被调用。
*/
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) { /* 遍历链表，释放内存 */
        if (dptr->data) {
            for (i = 0; i  qset; i++)    /*释放量子*/
                kfree(dptr->data);
            kfree(dptr->data);
            dptr->data = NULL;
        }
        next = dptr->next;
        kfree(dptr);
    }
    dev->size = 0;    /*重设scull_devices*/
    dev->quantum = scull_quantum;
    dev->qset = scull_qset;
    dev->data = NULL;
    return 0;
}
/*
scull_trim的实现相当于遍历了链表，先用dptr指针作为游标，指向每一个scull_qset,再通过量子集的大小dev->qset，在for循环中对dptr->data中的每一个量子进行释放。dptr->data是一个指针数组，所以kfree的参数为dptr->data。把量子集释放后再释放dptr->data.接着通过next指针移动游标，再释放当前的dptr。完整的内存释放后再对scull_devices初始化。
*/
以下是scull_trim函数的图解

待续....


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