#include <linux/fs.h>
#include <linux/version.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/blkdev.h>

#define BD_MAJOR 242
#define SIZE_IN_KBYTES (8*1024)

MODULE_LICENSE("GPL");

static struct gendisk *disk;
static struct request_queue *bdqueue;
static char *DiscSpace;
static struct block_device_operations bdops = {
  .owner           = THIS_MODULE,
};

static int bdMakeRequest( request_queue_t *q, struct bio *bio )
{
  char *kaddr, *maddr;
  struct bio_vec *bvec;
  int segnr, BytesTransferred=0;

  blk_queue_bounce( q, &bio );
  bio_for_each_segment( bvec, bio, segnr ) {
    kaddr = bio_data(bio);
    maddr = DiscSpace + (512 * bio->bi_sector);
    BytesTransferred += bio->bi_size;
    if( bio_data_dir( bio )==READ || bio_data_dir( bio )==READA ) {
      memcpy( kaddr, maddr, bio->bi_size );
    } else {
      memcpy( maddr, kaddr, bio->bi_size );
    }
  }
  bio_endio( bio, BytesTransferred, 0 );
  return 0;
}

static int __init ModInit(void)
{
  if( register_blkdev(BD_MAJOR, "bdsample" )) {
    printk("blockdevice: Majornummer %d not free.", BD_MAJOR);
    return -EIO;
  }
  if( !(DiscSpace=vmalloc(SIZE_IN_KBYTES*1024)) ) {
    printk("vmalloc failed ...\n");
    goto out_no_mem;
  }
  bdqueue = blk_alloc_queue( GFP_KERNEL );
  blk_queue_make_request( bdqueue, bdMakeRequest );
  disk = alloc_disk(1);
  if( !disk ) {
    printk("alloc_disk failed ...\n");
    goto out;
  }
  disk->major = BD_MAJOR;
  disk->first_minor = 0;
  disk->fops = &bdops;
  disk->queue = bdqueue;
  sprintf(disk->disk_name, "bd0");
  set_capacity( disk, (SIZE_IN_KBYTES*1024)>>9 ); // in 512 Byte Bloecke
  add_disk( disk );
  return 0;
 out:
  vfree( DiscSpace );
 out_no_mem:
  unregister_blkdev(BD_MAJOR, "bdsample" );
  return -EIO;
}

static void __exit ModExit(void)
{
  unregister_blkdev(BD_MAJOR, "bdsample" );
  del_gendisk(disk);
  put_disk( disk );
  blk_cleanup_queue( bdqueue );
  vfree( DiscSpace );
}

module_init( ModInit );
module_exit( ModExit );