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