ifreq_linux.go

     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
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