内核直接读取硬盘固定扇区的代码

块缓存 struct buffer_head 用来保存从磁盘读取到的数据，而 struct page 是文件的缓存，在文件层面上的数据会缓存到page里，所以内核里直接读取某个固定的扇区可以利用 struct buffer_head，读取的速度会快一些；以下是实现的代码：

 

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/msdos_fs.h>
#include <linux/fcntl.h>
#include <linux/delay.h>

static int set_size = 512;
static int nr = -1;
static char *devn = "/dev/sda";

module_param(set_size,int,S_IRUGO);
MODULE_PARM_DESC(set_size,"how many bytes you want to read,not more than 4096");
module_param(nr,long,S_IRUGO);
MODULE_PARM_DESC(nr,"which sectors you want to read");
module_param(devn,charp,S_IRUGO);
MODULE_PARM_DESC(devn,"which device");
MODULE_LICENSE("GPL");

static struct block_device *bdev;
static char *usage = "You can change the value:set_size nr devn";

static int __init init_read(void)
{
    struct buffer_head *bh = NULL;
    int size;
    if(nr == -1)
    {
        printk("Using this programm,you need set \"nr\"\n");
        printk("%s\n",usage);
        return -1;
    }
    printk("read disk\n");
    bdev = open_bdev_excl(devn,0x8000,NULL);
    if(IS_ERR(bdev))
    {
        printk("open failed\n");
        return PTR_ERR(bdev);
    }
    
    size = bdev_hardsect_size(bdev);
    printk("size = %d\n",size);
    
    if(set_blocksize(bdev,set_size)){
        printk("set block size error\n");
        return -1;
    }
    /* read disk */
    bh = __bread(bdev,nr,set_size);
    if(bh == NULL)
        return 0;
    //if you want to modify the disk contents,do this operations

    memset(bh->b_data,0x30,set_size);
    set_buffer_uptodate(bh);
    /* write disk */
    mark_buffer_dirty(bh);
    if(bh)
        brelse(bh);
    return 0;
}


static void __exit exit_read(void)
{
    printk("exit\n");
    close_bdev_excl(bdev);
}

module_init(init_read);
module_exit(exit_read);