message_linux.go

// SPDX-License-Identifier: Apache-2.0
// Copyright 2014 Docker, Inc.
// Copyright 2023 Unikraft GmbH and The KraftKit Authors

package libmocktainer

import (
	"fmt"
	"math"

	"github.com/vishvananda/netlink/nl"
	"golang.org/x/sys/unix"
)

// list of known message types we want to send to bootstrap program
// The number is randomly chosen to not conflict with known netlink types
const (
	InitMsg        uint16 = 62000
	CloneFlagsAttr uint16 = 27281
	NsPathsAttr    uint16 = 27282
)

type Int32msg struct {
	Type  uint16
	Value uint32
}

// Serialize serializes the message.
// Int32msg has the following representation
// | nlattr len | nlattr type |
// | uint32 value             |
func (msg *Int32msg) Serialize() []byte {
	buf := make([]byte, msg.Len())
	native := nl.NativeEndian()
	native.PutUint16(buf[0:2], uint16(msg.Len()))
	native.PutUint16(buf[2:4], msg.Type)
	native.PutUint32(buf[4:8], msg.Value)
	return buf
}

func (msg *Int32msg) Len() int {
	return unix.NLA_HDRLEN + 4
}

// Bytemsg has the following representation
// | nlattr len | nlattr type |
// | value              | pad |
type Bytemsg struct {
	Type  uint16
	Value []byte
}

func (msg *Bytemsg) Serialize() []byte {
	l := msg.Len()
	if l > math.MaxUint16 {
		// We cannot return nil nor an error here, so we panic with
		// a specific type instead, which is handled via recover in
		// bootstrapData.
		panic(netlinkError{fmt.Errorf("netlink: cannot serialize bytemsg of length %d (larger than UINT16_MAX)", l)})
	}
	buf := make([]byte, (l+unix.NLA_ALIGNTO-1) & ^(unix.NLA_ALIGNTO-1))
	native := nl.NativeEndian()
	native.PutUint16(buf[0:2], uint16(l))
	native.PutUint16(buf[2:4], msg.Type)
	copy(buf[4:], msg.Value)
	return buf
}

func (msg *Bytemsg) Len() int {
	return unix.NLA_HDRLEN + len(msg.Value) + 1 // null-terminated
}