char rBuf[208 * 512] = {0};
static int dev_reset(void) {
    char *dev_file = "(hd0,2,a)+2048";
    grub_file_t file;
    grub_disk_t disk;
    grub_disk_addr_t part_start = 0;
    grub_disk_addr_t bt_sector = 0;

    unsigned bt_offset = 0;
    unsigned bt_length = 0;

    auto void NESTED_FUNC_ATTR read_hook (grub_disk_addr_t sector,
                                          unsigned offset,
                                          unsigned length);

    void NESTED_FUNC_ATTR read_hook (grub_disk_addr_t sector,
                    unsigned offset, unsigned length) {
        if( bt_sector == 0 ) {
        bt_sector = sector;
        bt_offset = offset;
        bt_length = length;
        grub_printf("bt_sector = %llu\nbt_offset = %u\nbt_length = %u\n",
            bt_sector, bt_offset, bt_length);
        } else {
            grub_dprintf("bsd", "%s:%s:%d Still more...!\n",
                __FILE__, __FUNCTION__, __LINE__);
        }
    }

    file = grub_file_open(dev_file);
    if( !file ) {
         grub_printf("Error: Unable to open '%s' .\n", dev_file);
         return grub_errno;
    }

    if( ! file->device->disk ) {
        grub_printf("disk device required!\n");
        return grub_errno;
    }

    file->read_hook = read_hook;
    grub_file_read(file, rBuf, sizeof(rBuf));
    file->read_hook = 0;

    disk = file->device->disk;

    grub_printf("File size: %llu\ntotal_sectors = %llu", file->size,
            disk->total_sectors);


    if( disk->partition )
        part_start = grub_partition_get_start(disk->partition);
    else
        part_start = 0;

    grub_printf("%s[%d]: %llu\n", __FUNCTION__, __LINE__, part_start);

    if( bt_sector > part_start ) {
        part_start = bt_sector - part_start;
    }

    grub_printf("%s[%d]: %llu\n", __FUNCTION__, __LINE__, part_start);

    {
        int i=0;
        do {
            grub_printf("%x ",rBuf[i++]);
        } while(i<512);
    }

    grub_memset(nvbuf, 0, SECTOR_SIZE);

    if(grub_disk_write(disk, part_start, 0, SECTOR_SIZE, nvbuf) ) {
        grub_printf("%s %s:%d Disk write error!\n", __FILE__, __FUNCTION__, __LINE__);
        grub_printf("disk = %x\n part_start = %llu\n", (unsigned int)disk, part_start);
    } else
        grub_dprintf("bsd", "Device reset done!");

    grub_file_close(file);

    return grub_errno;
}