NAME
link_addr,
link_ntoa —
elementary address specification
routines for link level access
LIBRARY
library “libc”
SYNOPSIS
#include
<sys/types.h>
#include <sys/socket.h>
#include <net/if_dl.h>
void
link_addr(const
char *addr, struct
sockaddr_dl *sdl);
char *
link_ntoa(const
struct sockaddr_dl *sdl);
DESCRIPTION
The routinelink_addr()
interprets character strings representing link-level addresses, returning
binary information suitable for use in system calls. The routine
link_ntoa()
takes a link-level address and returns an ASCII string representing some of
the information present, including the link level address itself, and the
interface name or number, if present. This facility is experimental and is
still subject to change.
Prior to a call to
link_addr(),
sdl->sdl_len must be initialized to the size of the
link-level socket structure, typically sizeof(struct
sockaddr_dl).
For
link_addr(),
the string addr may contain an optional network
interface identifier of the form “name unit-number”, suitable
for the first argument to
ifconfig(8), followed in all cases by a colon and an interface
address in the form of groups of hexadecimal digits separated by periods.
Each group represents a byte of address; address bytes are filled left to
right from low order bytes through high order bytes.
Thus le0:8.0.9.13.d.30 represents an
ethernet address to be transmitted on the first Lance ethernet
interface.
RETURN VALUES
link_ntoa() always returns a null
terminated string. link_addr() has no return value
(See BUGS).
SEE ALSO
HISTORY
The link_addr() and
link_ntoa() functions appeared in
4.3BSD-Reno.
BUGS
The returned string for link_ntoa()
resides in a static memory area. If it would overflow this area,
link_ntoa() silently truncates the result.
The function link_addr() should diagnose
improperly formed input, and there should be an unambiguous way to recognize
this.
If the sdl_len field of the link socket
address sdl is 0, link_ntoa()
will not insert a colon before the interface address bytes. If this
translated address is given to link_addr() without
inserting an initial colon, the latter will not interpret it correctly.