150 lines
4.5 KiB
Go
150 lines
4.5 KiB
Go
// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build linux
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// +build linux
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package unix
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import (
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"bytes"
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"unsafe"
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)
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// Helpers for dealing with ifreq since it contains a union and thus requires a
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// lot of unsafe.Pointer casts to use properly.
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// An Ifreq is a type-safe wrapper around the raw ifreq struct. An Ifreq
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// contains an interface name and a union of arbitrary data which can be
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// accessed using the Ifreq's methods. To create an Ifreq, use the NewIfreq
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// function.
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//
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// Use the Name method to access the stored interface name. The union data
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// fields can be get and set using the following methods:
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// - Uint16/SetUint16: flags
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// - Uint32/SetUint32: ifindex, metric, mtu
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type Ifreq struct{ raw ifreq }
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// NewIfreq creates an Ifreq with the input network interface name after
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// validating the name does not exceed IFNAMSIZ-1 (trailing NULL required)
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// bytes.
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func NewIfreq(name string) (*Ifreq, error) {
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// Leave room for terminating NULL byte.
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if len(name) >= IFNAMSIZ {
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return nil, EINVAL
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}
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var ifr ifreq
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copy(ifr.Ifrn[:], name)
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return &Ifreq{raw: ifr}, nil
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}
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// TODO(mdlayher): get/set methods for hardware address sockaddr, char array, etc.
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// Name returns the interface name associated with the Ifreq.
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func (ifr *Ifreq) Name() string {
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// BytePtrToString requires a NULL terminator or the program may crash. If
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// one is not present, just return the empty string.
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if !bytes.Contains(ifr.raw.Ifrn[:], []byte{0x00}) {
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return ""
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}
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return BytePtrToString(&ifr.raw.Ifrn[0])
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}
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// According to netdevice(7), only AF_INET addresses are returned for numerous
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// sockaddr ioctls. For convenience, we expose these as Inet4Addr since the Port
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// field and other data is always empty.
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// Inet4Addr returns the Ifreq union data from an embedded sockaddr as a C
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// in_addr/Go []byte (4-byte IPv4 address) value. If the sockaddr family is not
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// AF_INET, an error is returned.
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func (ifr *Ifreq) Inet4Addr() ([]byte, error) {
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raw := *(*RawSockaddrInet4)(unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0]))
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if raw.Family != AF_INET {
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// Cannot safely interpret raw.Addr bytes as an IPv4 address.
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return nil, EINVAL
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}
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return raw.Addr[:], nil
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}
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// SetInet4Addr sets a C in_addr/Go []byte (4-byte IPv4 address) value in an
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// embedded sockaddr within the Ifreq's union data. v must be 4 bytes in length
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// or an error will be returned.
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func (ifr *Ifreq) SetInet4Addr(v []byte) error {
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if len(v) != 4 {
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return EINVAL
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}
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var addr [4]byte
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copy(addr[:], v)
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ifr.clear()
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*(*RawSockaddrInet4)(
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unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0]),
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) = RawSockaddrInet4{
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// Always set IP family as ioctls would require it anyway.
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Family: AF_INET,
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Addr: addr,
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}
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return nil
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}
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// Uint16 returns the Ifreq union data as a C short/Go uint16 value.
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func (ifr *Ifreq) Uint16() uint16 {
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return *(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0]))
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}
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// SetUint16 sets a C short/Go uint16 value as the Ifreq's union data.
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func (ifr *Ifreq) SetUint16(v uint16) {
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ifr.clear()
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*(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0])) = v
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}
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// Uint32 returns the Ifreq union data as a C int/Go uint32 value.
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func (ifr *Ifreq) Uint32() uint32 {
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return *(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0]))
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}
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// SetUint32 sets a C int/Go uint32 value as the Ifreq's union data.
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func (ifr *Ifreq) SetUint32(v uint32) {
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ifr.clear()
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*(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0])) = v
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}
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// clear zeroes the ifreq's union field to prevent trailing garbage data from
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// being sent to the kernel if an ifreq is reused.
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func (ifr *Ifreq) clear() {
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for i := range ifr.raw.Ifru {
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ifr.raw.Ifru[i] = 0
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}
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}
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// TODO(mdlayher): export as IfreqData? For now we can provide helpers such as
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// IoctlGetEthtoolDrvinfo which use these APIs under the hood.
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// An ifreqData is an Ifreq which carries pointer data. To produce an ifreqData,
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// use the Ifreq.withData method.
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type ifreqData struct {
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name [IFNAMSIZ]byte
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// A type separate from ifreq is required in order to comply with the
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// unsafe.Pointer rules since the "pointer-ness" of data would not be
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// preserved if it were cast into the byte array of a raw ifreq.
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data unsafe.Pointer
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// Pad to the same size as ifreq.
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_ [len(ifreq{}.Ifru) - SizeofPtr]byte
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}
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// withData produces an ifreqData with the pointer p set for ioctls which require
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// arbitrary pointer data.
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func (ifr Ifreq) withData(p unsafe.Pointer) ifreqData {
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return ifreqData{
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name: ifr.raw.Ifrn,
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data: p,
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}
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}
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