块设备驱动1--自编ramdisk(在linux-3.2.36上的新接口)

来源：互联网发布：软件防破解编辑：程序博客网时间：2024/06/05 20:18

这是块设备驱动的第一期，我们就从ldd3的sbull开始吧，但是ldd3用的linux版本太老了，你直接用它的例子在linux-3.2.x上是很麻烦的。

我主要做的就是在高版本上的移植。

里面有个NOQUEUE宏，可以选择不用一个请求队列。

自己对着ldd3中的讲解看看吧

/*********************************** Copyright(C), 2013 LDP FileName:  bdev.c Author:     Date:           Description:   History:        Author       Date            Desc************************************/#include <linux/module.h>//MODULE_*#include <linux/fs.h>//fops#include <linux/init.h>//printk#include <linux/slab.h>//kzalloc() kfree()#include <linux/blkdev.h>//register_blkdev#include <linux/bio.h>//strucut bio#include <linux/spinlock.h>//spinlock#include <linux/hdreg.h>    //HDIO_GETGEO#include <asm/uaccess.h>//copy_to_user#define DEV_NAME "vDisk"#define NOQUEUE//不用一个请求队列 #define vDisk_MINORS 1 //磁盘分区数#define HARDSECT_SIZE       512 //硬件的扇区大小#define KERNEL_SECTOR_SIZE    512 //内核与快设备驱动交互的扇区单位#define SECTOR_CNT         1024 //扇区数    /*****************************************************              module description *****************************************************/MODULE_LICENSE("GPL");//GPL, GPL v2, GPL and additional rights, Dual BSD/GPL, Dual MPL/GPL, Proprietary.MODULE_AUTHOR("...");MODULE_DESCRIPTION("...");MODULE_VERSION("...");MODULE_ALIAS("...");/****************************************************/static int vDisk_major = 0;module_param(vDisk_major, int, 0);/***************************************************/struct LDP_vDisk{    int size;    u8 *data;    struct gendisk *gd;    struct request_queue *queue;     bool media_change;    spinlock_t lock;};/****************************************************               request operation****************************************************/static void vDisk_transfer(struct LDP_vDisk *dev, unsigned long sector,        unsigned long nsect, char *buffer, int write){    unsigned long offset = sector * KERNEL_SECTOR_SIZE;    unsigned long nbytes = nsect * KERNEL_SECTOR_SIZE;    if ((offset + nbytes) > dev->size)     {        printk (KERN_NOTICE "Beyond-end write (%ld %ld)\n", offset, nbytes);        return;    }    if (write)    {        memcpy(dev->data + offset, buffer, nbytes);    }    else    {        memcpy(buffer, dev->data + offset, nbytes);    }}static int vDisk_xfer_bio(struct LDP_vDisk *dev, struct bio *bio){    int i;    struct bio_vec *bvec;    sector_t sector = bio->bi_sector;    char *buffer;    /* Do each segment independently. */    bio_for_each_segment(bvec, bio, i)     {        buffer = __bio_kmap_atomic(bio, i, KM_USER0);        vDisk_transfer(dev, sector, bio_cur_bytes(bio) >> 9, buffer, bio_data_dir(bio) == WRITE);        sector += bio_cur_bytes(bio) >> 9;        __bio_kunmap_atomic(bio, KM_USER0);    }    return 0; /* Always "succeed" */}#ifdef NOQUEUEstatic void vDisk_make_request(struct request_queue *q, struct bio *bio){    struct LDP_vDisk *dev = q->queuedata;    int status;    status = vDisk_xfer_bio(dev, bio);    bio_endio(bio, status);  }#elsestatic void vDisk_request(struct request_queue *q){    struct request *req;    //int sectors_xferred = 0;    struct bio *bio;    struct LDP_vDisk *dev = q->queuedata;    req = blk_fetch_request(q);    while (req != NULL)    {        if (req->cmd_type != REQ_TYPE_FS)//文件系统请求        {             __blk_end_request_all(req, 1);             continue;        }                __rq_for_each_bio(bio, req)        {            vDisk_xfer_bio(dev, bio);        }        if (!__blk_end_request_cur(req, 0)) //通知设备层，        {            //add_disk_randomness(req->rq_disk);//for random            req = blk_fetch_request(q);        }    }}#endif/***************************************************//* * Open and close. */static int vDisk_open(struct block_device *bdevice, fmode_t fmt){    return 0;}static int vDisk_release(struct gendisk * gdisk, fmode_t fmt){    return 0;}static struct gendisk *vdisk_gendisk;static struct kobject *vdisk_find(dev_t dev, int *part, void *data){        *part = 0;        return get_disk(vdisk_gendisk);}/* * The device operations structure. */static struct block_device_operations vDisk_ops = {    .owner           = THIS_MODULE,    .open            = vDisk_open,    .release         = vDisk_release,};static struct LDP_vDisk *vDisk_dev = NULL;static int __init vDisk_init(void){    int ret = 0;    vDisk_dev = kzalloc(sizeof(struct LDP_vDisk), GFP_KERNEL);    if (vDisk_dev == NULL)    {        ret = -ENOMEM;        goto fail5;    }    vDisk_dev->size = SECTOR_CNT * HARDSECT_SIZE;    vDisk_dev->data = kzalloc(vDisk_dev->size, GFP_KERNEL);    if (vDisk_dev->data == NULL)    {        ret = -ENOMEM;        goto fail4;     }      spin_lock_init(&vDisk_dev->lock);    vDisk_dev->media_change = 0;    vdisk_gendisk = vDisk_dev->gd = alloc_disk(vDisk_MINORS);    if (vDisk_dev->gd == NULL)    {         ret = -1;        goto fail3;    }    vDisk_major = register_blkdev(vDisk_major, DEV_NAME);    if (vDisk_major <= 0)    {        ret = -EIO;        goto fail2;    }#ifdef NOQUEUE    vDisk_dev->queue = blk_alloc_queue(GFP_KERNEL);    if (vDisk_dev->queue == NULL)    {        ret = -1;        goto fail1;    }       blk_queue_make_request(vDisk_dev->queue, vDisk_make_request);#else    vDisk_dev->queue = blk_init_queue(vDisk_request, &vDisk_dev->lock);    if (vDisk_dev->queue == NULL)    {        ret = -1;        goto fail1;    }#endif    //blk_queue_logical_block_size(vDisk_dev->queue, HARDSECT_SIZE);    blk_queue_max_hw_sectors(vDisk_dev->queue, SECTOR_CNT);    vDisk_dev->queue->queuedata = vDisk_dev;    vDisk_dev->gd->major = vDisk_major;    vDisk_dev->gd->first_minor = 0;    vDisk_dev->gd->fops = &vDisk_ops;    vDisk_dev->gd->queue = vDisk_dev->queue;    vDisk_dev->gd->private_data = vDisk_dev;    snprintf (vDisk_dev->gd->disk_name, 32, DEV_NAME);    set_capacity(vDisk_dev->gd, SECTOR_CNT * (HARDSECT_SIZE / KERNEL_SECTOR_SIZE));    add_disk(vDisk_dev->gd);    blk_register_region(MKDEV(vDisk_major, 0), 1, THIS_MODULE, vdisk_find, NULL, NULL);    return ret;fail1:    unregister_blkdev(vDisk_major, DEV_NAME);fail2:    del_gendisk(vDisk_dev->gd);fail3:    kfree(vDisk_dev->data);fail4:    kfree(vDisk_dev);fail5:    return ret;}static void __exit vDisk_exit(void){    blk_unregister_region(MKDEV(vDisk_major, 0), 1);    if (vDisk_dev->gd)     {        del_gendisk(vDisk_dev->gd);        put_disk(vDisk_dev->gd);    }#ifdef NOQUEUE    blk_put_queue(vDisk_dev->queue);#else    blk_cleanup_queue(vDisk_dev->queue);#endif    unregister_blkdev(vDisk_major, DEV_NAME);    kfree(vDisk_dev->data);    kfree(vDisk_dev);}module_init(vDisk_init);module_exit(vDisk_exit);

我的板子遇到这个问题。

http://blog.chinaunix.net/uid-22731254-id-3948456.html

已解决！

你可以想我的方法执行：

内核中的ramdisk使用的就是不用一个请求队列，原因：ldd3原话

前面, 我们已经讨论了内核所作的在队列中优化请求顺序的工作; 这个工作包括排列请求和, 或许, 甚至延迟队列来允许一个预期的请求到达. 这些技术在
处理一个真正的旋转的磁盘驱动器时有助于系统的性能. 但是, 使用一个象 sbull 的设备它们是完全浪费了. 许多面向块的设备, 例如闪存阵列, 用于数
字相机的存储卡的读取器, 并且 RAM 盘真正地有随机存取的性能, 包含从高级的请求队列逻辑中获益. 其他设备, 例如软件 RAID 阵列或者被逻辑卷管理

者创建的虚拟磁盘, 没有这个块层的请求队列被优化的性能特征. 对于这类设备, 它最好直接从块层接收请求, 并且根本不去烦请求队列.

我顺便说一下，内核中IO调度的电梯算法有：

as(Anticipatory)

cfq(Complete Fairness Queueing)

deadline

noop(No Operation)

看我的虚拟机的

[root@localhost ramdisk]# cat /sys/block/hdc/queue/scheduler
noop anticipatory deadline [cfq]

你可以看一下/sys/block/ram0/下，没有queue。

对于我的例子，你可以选有或没有。

在嵌入式板子上，即使你选择有queue，也不一定涉及电梯算法，因为你还须别的配置。

我的板子就没有

# cat /sys/block/vDisk/queue/scheduler
none