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1 // Copyright 2021 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 //go:build linux
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6 // +build linux
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7
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8 package unix
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9
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10 import (
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11 "unsafe"
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12 )
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13
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14 // Helpers for dealing with ifreq since it contains a union and thus requires a
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15 // lot of unsafe.Pointer casts to use properly.
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16
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17 // An Ifreq is a type-safe wrapper around the raw ifreq struct. An Ifreq
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18 // contains an interface name and a union of arbitrary data which can be
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19 // accessed using the Ifreq's methods. To create an Ifreq, use the NewIfreq
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20 // function.
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21 //
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22 // Use the Name method to access the stored interface name. The union data
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23 // fields can be get and set using the following methods:
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24 // - Uint16/SetUint16: flags
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25 // - Uint32/SetUint32: ifindex, metric, mtu
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26 type Ifreq struct{ raw ifreq }
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27
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28 // NewIfreq creates an Ifreq with the input network interface name after
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29 // validating the name does not exceed IFNAMSIZ-1 (trailing NULL required)
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30 // bytes.
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31 func NewIfreq(name string) (*Ifreq, error) {
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32 // Leave room for terminating NULL byte.
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33 if len(name) >= IFNAMSIZ {
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34 return nil, EINVAL
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35 }
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36
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37 var ifr ifreq
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38 copy(ifr.Ifrn[:], name)
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39
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40 return &Ifreq{raw: ifr}, nil
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41 }
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42
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43 // TODO(mdlayher): get/set methods for hardware address sockaddr, char array, etc.
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44
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45 // Name returns the interface name associated with the Ifreq.
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46 func (ifr *Ifreq) Name() string {
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47 return ByteSliceToString(ifr.raw.Ifrn[:])
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48 }
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49
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50 // According to netdevice(7), only AF_INET addresses are returned for numerous
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51 // sockaddr ioctls. For convenience, we expose these as Inet4Addr since the Port
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52 // field and other data is always empty.
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53
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54 // Inet4Addr returns the Ifreq union data from an embedded sockaddr as a C
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55 // in_addr/Go []byte (4-byte IPv4 address) value. If the sockaddr family is not
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56 // AF_INET, an error is returned.
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57 func (ifr *Ifreq) Inet4Addr() ([]byte, error) {
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58 raw := *(*RawSockaddrInet4)(unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0]))
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59 if raw.Family != AF_INET {
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60 // Cannot safely interpret raw.Addr bytes as an IPv4 address.
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61 return nil, EINVAL
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62 }
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63
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64 return raw.Addr[:], nil
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65 }
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66
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67 // SetInet4Addr sets a C in_addr/Go []byte (4-byte IPv4 address) value in an
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68 // embedded sockaddr within the Ifreq's union data. v must be 4 bytes in length
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69 // or an error will be returned.
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70 func (ifr *Ifreq) SetInet4Addr(v []byte) error {
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71 if len(v) != 4 {
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72 return EINVAL
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73 }
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74
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75 var addr [4]byte
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76 copy(addr[:], v)
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77
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78 ifr.clear()
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79 *(*RawSockaddrInet4)(
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80 unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0]),
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81 ) = RawSockaddrInet4{
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82 // Always set IP family as ioctls would require it anyway.
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83 Family: AF_INET,
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84 Addr: addr,
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85 }
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86
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87 return nil
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88 }
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89
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90 // Uint16 returns the Ifreq union data as a C short/Go uint16 value.
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91 func (ifr *Ifreq) Uint16() uint16 {
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92 return *(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0]))
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93 }
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94
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95 // SetUint16 sets a C short/Go uint16 value as the Ifreq's union data.
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96 func (ifr *Ifreq) SetUint16(v uint16) {
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97 ifr.clear()
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98 *(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0])) = v
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99 }
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100
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101 // Uint32 returns the Ifreq union data as a C int/Go uint32 value.
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102 func (ifr *Ifreq) Uint32() uint32 {
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103 return *(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0]))
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104 }
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105
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106 // SetUint32 sets a C int/Go uint32 value as the Ifreq's union data.
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107 func (ifr *Ifreq) SetUint32(v uint32) {
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108 ifr.clear()
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109 *(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0])) = v
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110 }
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111
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112 // clear zeroes the ifreq's union field to prevent trailing garbage data from
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113 // being sent to the kernel if an ifreq is reused.
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114 func (ifr *Ifreq) clear() {
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115 for i := range ifr.raw.Ifru {
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116 ifr.raw.Ifru[i] = 0
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117 }
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118 }
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119
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120 // TODO(mdlayher): export as IfreqData? For now we can provide helpers such as
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121 // IoctlGetEthtoolDrvinfo which use these APIs under the hood.
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122
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123 // An ifreqData is an Ifreq which carries pointer data. To produce an ifreqData,
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124 // use the Ifreq.withData method.
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125 type ifreqData struct {
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126 name [IFNAMSIZ]byte
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127 // A type separate from ifreq is required in order to comply with the
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128 // unsafe.Pointer rules since the "pointer-ness" of data would not be
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129 // preserved if it were cast into the byte array of a raw ifreq.
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130 data unsafe.Pointer
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131 // Pad to the same size as ifreq.
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132 _ [len(ifreq{}.Ifru) - SizeofPtr]byte
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133 }
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134
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135 // withData produces an ifreqData with the pointer p set for ioctls which require
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136 // arbitrary pointer data.
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137 func (ifr Ifreq) withData(p unsafe.Pointer) ifreqData {
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138 return ifreqData{
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139 name: ifr.raw.Ifrn,
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140 data: p,
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141 }
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142 }
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