1 // Copyright 2021 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 //go:build linux 6 // +build linux 7 8 package unix 9 10 import ( 11 "unsafe" 12 ) 13 14 // Helpers for dealing with ifreq since it contains a union and thus requires a 15 // lot of unsafe.Pointer casts to use properly. 16 17 // An Ifreq is a type-safe wrapper around the raw ifreq struct. An Ifreq 18 // contains an interface name and a union of arbitrary data which can be 19 // accessed using the Ifreq's methods. To create an Ifreq, use the NewIfreq 20 // function. 21 // 22 // Use the Name method to access the stored interface name. The union data 23 // fields can be get and set using the following methods: 24 // - Uint16/SetUint16: flags 25 // - Uint32/SetUint32: ifindex, metric, mtu 26 type Ifreq struct{ raw ifreq } 27 28 // NewIfreq creates an Ifreq with the input network interface name after 29 // validating the name does not exceed IFNAMSIZ-1 (trailing NULL required) 30 // bytes. 31 func NewIfreq(name string) (*Ifreq, error) { 32 // Leave room for terminating NULL byte. 33 if len(name) >= IFNAMSIZ { 34 return nil, EINVAL 35 } 36 37 var ifr ifreq 38 copy(ifr.Ifrn[:], name) 39 40 return &Ifreq{raw: ifr}, nil 41 } 42 43 // TODO(mdlayher): get/set methods for hardware address sockaddr, char array, etc. 44 45 // Name returns the interface name associated with the Ifreq. 46 func (ifr *Ifreq) Name() string { 47 return ByteSliceToString(ifr.raw.Ifrn[:]) 48 } 49 50 // According to netdevice(7), only AF_INET addresses are returned for numerous 51 // sockaddr ioctls. For convenience, we expose these as Inet4Addr since the Port 52 // field and other data is always empty. 53 54 // Inet4Addr returns the Ifreq union data from an embedded sockaddr as a C 55 // in_addr/Go []byte (4-byte IPv4 address) value. If the sockaddr family is not 56 // AF_INET, an error is returned. 57 func (ifr *Ifreq) Inet4Addr() ([]byte, error) { 58 raw := *(*RawSockaddrInet4)(unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0])) 59 if raw.Family != AF_INET { 60 // Cannot safely interpret raw.Addr bytes as an IPv4 address. 61 return nil, EINVAL 62 } 63 64 return raw.Addr[:], nil 65 } 66 67 // SetInet4Addr sets a C in_addr/Go []byte (4-byte IPv4 address) value in an 68 // embedded sockaddr within the Ifreq's union data. v must be 4 bytes in length 69 // or an error will be returned. 70 func (ifr *Ifreq) SetInet4Addr(v []byte) error { 71 if len(v) != 4 { 72 return EINVAL 73 } 74 75 var addr [4]byte 76 copy(addr[:], v) 77 78 ifr.clear() 79 *(*RawSockaddrInet4)( 80 unsafe.Pointer(&ifr.raw.Ifru[:SizeofSockaddrInet4][0]), 81 ) = RawSockaddrInet4{ 82 // Always set IP family as ioctls would require it anyway. 83 Family: AF_INET, 84 Addr: addr, 85 } 86 87 return nil 88 } 89 90 // Uint16 returns the Ifreq union data as a C short/Go uint16 value. 91 func (ifr *Ifreq) Uint16() uint16 { 92 return *(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0])) 93 } 94 95 // SetUint16 sets a C short/Go uint16 value as the Ifreq's union data. 96 func (ifr *Ifreq) SetUint16(v uint16) { 97 ifr.clear() 98 *(*uint16)(unsafe.Pointer(&ifr.raw.Ifru[:2][0])) = v 99 } 100 101 // Uint32 returns the Ifreq union data as a C int/Go uint32 value. 102 func (ifr *Ifreq) Uint32() uint32 { 103 return *(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0])) 104 } 105 106 // SetUint32 sets a C int/Go uint32 value as the Ifreq's union data. 107 func (ifr *Ifreq) SetUint32(v uint32) { 108 ifr.clear() 109 *(*uint32)(unsafe.Pointer(&ifr.raw.Ifru[:4][0])) = v 110 } 111 112 // clear zeroes the ifreq's union field to prevent trailing garbage data from 113 // being sent to the kernel if an ifreq is reused. 114 func (ifr *Ifreq) clear() { 115 for i := range ifr.raw.Ifru { 116 ifr.raw.Ifru[i] = 0 117 } 118 } 119 120 // TODO(mdlayher): export as IfreqData? For now we can provide helpers such as 121 // IoctlGetEthtoolDrvinfo which use these APIs under the hood. 122 123 // An ifreqData is an Ifreq which carries pointer data. To produce an ifreqData, 124 // use the Ifreq.withData method. 125 type ifreqData struct { 126 name [IFNAMSIZ]byte 127 // A type separate from ifreq is required in order to comply with the 128 // unsafe.Pointer rules since the "pointer-ness" of data would not be 129 // preserved if it were cast into the byte array of a raw ifreq. 130 data unsafe.Pointer 131 // Pad to the same size as ifreq. 132 _ [len(ifreq{}.Ifru) - SizeofPtr]byte 133 } 134 135 // withData produces an ifreqData with the pointer p set for ioctls which require 136 // arbitrary pointer data. 137 func (ifr Ifreq) withData(p unsafe.Pointer) ifreqData { 138 return ifreqData{ 139 name: ifr.raw.Ifrn, 140 data: p, 141 } 142 } 143