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;
}
#p#副标题#e#
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);
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