1.\" Copyright (c) 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Donn Seeley at BSDI. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.Dd May 7, 2025 32.Dt LINK_ADDR 3 33.Os 34.Sh NAME 35.Nm link_addr , 36.Nm link_ntoa , 37.Nm link_ntoa_r 38.Nd elementary address specification routines for link level access 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/socket.h 44.In net/if_dl.h 45.Ft void 46.Fn link_addr "const char *addr" "struct sockaddr_dl *sdl" 47.Ft char * 48.Fn link_ntoa "const struct sockaddr_dl *sdl" 49.Ft int 50.Fn link_ntoa_r "const struct sockaddr_dl *sdl" "char *obuf" "size_t *buflen" 51.Sh DESCRIPTION 52The routine 53.Fn link_addr 54interprets character strings representing 55link-level addresses, returning binary information suitable 56for use in system calls. 57.Pp 58The routine 59.Fn link_ntoa 60takes 61a link-level 62address and returns an 63.Tn ASCII 64string representing some of the information present, 65including the link level address itself, and the interface name 66or number, if present. 67The returned string is stored in a static buffer. 68This facility is experimental and is 69still subject to change. 70.Pp 71The routine 72.Fn link_ntoa_r 73behaves like 74.Fn link_ntoa , 75except the string is placed in the provided buffer instead of a static 76buffer. 77The caller should initialize 78.Fa buflen 79to the number of bytes available in 80.Fa obuf . 81On return, 82.Fa buflen 83is set to the actual number of bytes required for the output buffer, 84including the NUL terminator. 85If 86.Fa obuf 87is NULL, then 88.Fa buflen 89is set as described, but nothing is written. 90This may be used to determine the required length of the buffer before 91calling 92.Fn link_ntoa_r 93a second time. 94.Pp 95For 96.Fn link_addr , 97the string 98.Fa addr 99may contain 100an optional network interface identifier of the form 101.Dq "name unit-number" , 102suitable for the first argument to 103.Xr ifconfig 8 , 104followed in all cases by a colon and 105an interface address in the form of 106groups of hexadecimal digits 107separated by periods. 108Each group represents a byte of address; 109address bytes are filled left to right from 110low order bytes through high order bytes. 111.Pp 112.\" A regular expression may make this format clearer: 113.\" .Bd -literal -offset indent 114.\" ([a-z]+[0-9]+:)?[0-9a-f]+(\e.[0-9a-f]+)* 115.\" .Ed 116.\" .Pp 117Thus 118.Li le0:8.0.9.13.d.30 119represents an ethernet address 120to be transmitted on the first Lance ethernet interface. 121.Sh RETURN VALUES 122The 123.Fn link_ntoa 124function 125always returns a null terminated string. 126.Pp 127The 128.Fn link_ntoa_r 129function returns 0 on success, or -1 if the provided buffer was not 130large enough; in the latter case, the contents of the buffer are 131indeterminate, but a trailing NUL will always be written if the buffer 132was at least one byte in size. 133.Pp 134The 135.Fn link_addr 136function 137has no return value. 138(See 139.Sx BUGS . ) 140.Sh SEE ALSO 141.Xr getnameinfo 3 142.Sh HISTORY 143The 144.Fn link_addr 145and 146.Fn link_ntoa 147functions appeared in 148.Bx 4.3 Reno . 149The 150.Fn link_ntoa_r 151function appeared in 152.Fx 15.0 . 153.Sh BUGS 154The returned values for link_ntoa 155reside in a static memory area. 156.Pp 157The function 158.Fn link_addr 159should diagnose improperly formed input, and there should be an unambiguous 160way to recognize this. 161.Pp 162If the 163.Va sdl_len 164field of the link socket address 165.Fa sdl 166is 0, 167.Fn link_ntoa 168will not insert a colon before the interface address bytes. 169If this translated address is given to 170.Fn link_addr 171without inserting an initial colon, 172the latter will not interpret it correctly. 173