linux block framework(3) - ramdisk driver

• 案例ramdisk 源码

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

#include <linux/fs.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/vmalloc.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>

#define RAMHD_NAME              "ramhd"
#define RAMHD_MAX_DEVICE        2
#define RAMHD_MAX_PARTITIONS    4

#define RAMHD_SECTOR_SIZE       512
#define RAMHD_SECTORS           16
#define RAMHD_HEADS             4
#define RAMHD_CYLINDERS         256

#define RAMHD_SECTOR_TOTAL      (RAMHD_SECTORS * RAMHD_HEADS * RAMHD_CYLINDERS)
#define RAMHD_SIZE              (RAMHD_SECTOR_SIZE * RAMHD_SECTOR_TOTAL) //8MB

typedef struct{
    unsigned char *data;
    struct request_queue *queue;
    struct gendisk  *gd;
}RAMHD_DEV;

char *sdisk[RAMHD_MAX_DEVICE] = {NULL,};
EXPORT_SYMBOL_GPL(sdisk);

static RAMHD_DEV *rdev[RAMHD_MAX_DEVICE] = {NULL,};

static dev_t ramhd_major;

static int ramhd_space_init(void)
{
    int i;
    int err = 0;
    for(i = 0; i < RAMHD_MAX_DEVICE; i++){
        sdisk[i] = vmalloc(RAMHD_SIZE);
        if(!sdisk[i]){
            printk("vmalloc failed!");
            err = -ENOMEM;
            return err;
        }
        printk("sdisk[%d]=%p\n", i, sdisk[i]);
        memset(sdisk[i], 0, RAMHD_SIZE);
    }

    return err;
}

static void ramhd_space_clean(void)
{
    int i;
    for(i = 0; i < RAMHD_MAX_DEVICE; i++){
        vfree(sdisk[i]);
    }
}

static int ramhd_open(struct block_device *bdev, fmode_t mode)
{
    return 0;
}

static int ramhd_release(struct gendisk *gd, fmode_t mode)
{   
    return 0;
}

static int ramhd_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg)
{
    int err;
    struct hd_geometry geo;

    switch(cmd)
    {
        case HDIO_GETGEO:
            err = !access_ok(VERIFY_WRITE, arg, sizeof(geo));
            if(err) return -EFAULT;
        
            geo.cylinders = RAMHD_CYLINDERS;
            geo.heads = RAMHD_HEADS;
            geo.sectors = RAMHD_SECTORS;
            geo.start = get_start_sect(bdev);
            if(copy_to_user((void *)arg, &geo, sizeof(geo)))
                return -EFAULT;
            return 0;
    }
            
    return -ENOTTY;
}

static struct block_device_operations ramhd_fops =
{   .owner = THIS_MODULE,
    .open = ramhd_open,
    .release = ramhd_release,
    .ioctl = ramhd_ioctl,
};

static int ramhd_make_request(struct request_queue *q, struct bio *bio)
{
    char *pRHdata;
    char *pBuffer;
    struct bio_vec *bvec;
    int i;
    int err = 0;
    
    struct block_device *bdev = bio->bi_bdev;
	RAMHD_DEV *pdev = bdev->bd_disk->private_data;
    
    if(((bio->bi_sector * RAMHD_SECTOR_SIZE) + bio->bi_size) > RAMHD_SIZE){
        err = -EIO;
        goto out;
    }
    
    pRHdata = pdev->data + (bio->bi_sector * RAMHD_SECTOR_SIZE);
    
    bio_for_each_segment(bvec, bio, i) {
        pBuffer = kmap(bvec->bv_page) + bvec->bv_offset;
		switch(bio_data_dir(bio))
        {
            case READ:
                memcpy(pBuffer, pRHdata, bvec->bv_len);
                flush_dcache_page(bvec->bv_page);
                break;
            case WRITE:
                flush_dcache_page(bvec->bv_page);
                memcpy(pRHdata, pBuffer, bvec->bv_len);
                break;
            default:
                kunmap(bvec->bv_page);
                goto out;
        }
        kunmap(bvec->bv_page);
        pRHdata += bvec->bv_len;
	}
out:
	bio_endio(bio, err);
    return 0;      
}

static int alloc_ramdev(void)
{
    int i;
    for(i = 0; i < RAMHD_MAX_DEVICE; i++){
        rdev[i] = kzalloc(sizeof(RAMHD_DEV), GFP_KERNEL);
        if(!rdev[i])
            return -ENOMEM;
    }
    return 0;
}

static void clean_ramdev(void)
{
    int i;
    for(i = 0; i < RAMHD_MAX_DEVICE; i++){
        if(rdev[i])
            kfree(rdev[i]);
    }   
}       

static int __init ramhd_init(void)
{
    int i;
    int err;
    
    err = ramhd_space_init();
    if(err)
        return err;
    alloc_ramdev();
    
    ramhd_major = register_blkdev(0, RAMHD_NAME);
    
    for(i = 0; i < RAMHD_MAX_DEVICE; i++)
    {  
        rdev[i]->data = sdisk[i];
        rdev[i]->queue = blk_alloc_queue(GFP_KERNEL);
        blk_queue_make_request(rdev[i]->queue, ramhd_make_request);
        rdev[i]->gd = alloc_disk(RAMHD_MAX_PARTITIONS);
        rdev[i]->gd->major = ramhd_major;
        rdev[i]->gd->first_minor = i * RAMHD_MAX_PARTITIONS;
        rdev[i]->gd->fops = &ramhd_fops;
        rdev[i]->gd->queue = rdev[i]->queue;
        rdev[i]->gd->private_data = rdev[i];
        sprintf(rdev[i]->gd->disk_name, "ramhd%c", 'a'+i);
        rdev[i]->gd->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
        set_capacity(rdev[i]->gd, RAMHD_SECTOR_TOTAL);
        add_disk(rdev[i]->gd);
    }
    return 0;
}

static void __exit ramhd_exit(void)
{
    int i;
    
    for(i = 0; i < RAMHD_MAX_DEVICE; i++)
    {
        del_gendisk(rdev[i]->gd);
        put_disk(rdev[i]->gd);
        blk_cleanup_queue(rdev[i]->queue);  
    } 
    clean_ramdev();
    ramhd_space_clean();
    unregister_blkdev(ramhd_major,RAMHD_NAME);    
}

module_init(ramhd_init);
module_exit(ramhd_exit);

MODULE_AUTHOR("dennis chen @AMDLinuxFGL");
MODULE_DESCRIPTION("The ramdisk implementation with request function");
MODULE_LICENSE("GPL");

  编译，执行insmod ramhd_mkreq.ko。

• cat /proc/devices，发现生成 253 ramhd。

Block devices:
  1 ramdisk
259 blkext
  7 loop
  8 sd
 65 sd
134 sd
135 sd
179 mmc
253 ramhd

• cd /dev/block (发现在/dev下新增两个结点)

ls -l ramh*
brw------- root     root     253,   0 2012-01-01 08:20 ramhda
brw------- root     root     253,   4 2012-01-01 08:20 ramhdb

  两个块设备ramhda，ramhdb被加入系统中，主设备号为253，次设备号分别是0和4。

a）make 一下，生成ramdisk.ko；

b）编译好了之后，就可以安装驱动了，在linux下是这么做的，sudo insmod ramdisk.ko；

c）安装好了，利用ls /dev/ramhd*， 就会发现在/dev下新增两个结点，即/dev/ramhda和/dev/ramhdb；

d）不妨选择其中一个节点进行分区处理， sudo fdisk /dev/ramhda，简单处理的话就建立一个分区， 生成/dev/ramhda1；

e）创建文件系统，sudo mkfs.ext3 /dev/ramhda1；

f）有了上面的文件系统，就可以进行mount处理，不妨sudo mount /dev/ramhda1 /mnt；

g）上面都弄好了，大家就可以copy、delete文件试试了，是不是很简单。