VAX_BOOT_BLOCK_OFFSET
rv = pread(params->fsfd, &bb, sizeof(bb), VAX_BOOT_BLOCK_OFFSET);
rv = pwrite(params->fsfd, &bb, sizeof(bb), VAX_BOOT_BLOCK_OFFSET);
rv = pread(params->fsfd, oldbb, sizeof(oldbb), VAX_BOOT_BLOCK_OFFSET);