You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ioctl.go
    path of file: ./repos/podman/vendor/github.com/containers/storage/pkg/devicemapper
    
    the code of the file until where you have to start completion: //go:build linux && cgo
// +build linux,cgo

package devicemapper

import (
	"unsafe"

	"golang.org/x/sys/unix"
    
func ioctlBlkDiscard(fd uintptr, offset, length uint64) error {
	var r [2]uint64
	r[0] = offset
	r[1] = length

	if _, _, err := unix.Syscall(unix.SYS_IOCTL, fd, BlkDiscard, uintptr(unsafe.Pointer(&r[0]))); err != 0 {
		return err
	}
	return nil
}