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ifreq_linux.go (4387B)

      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 }