usr/src/sys/net/if_dl.h

/*
 * Copyright (c) 1990 Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 *
 *      @(#)if_dl.h     7.1 (Berkeley) %G%
 */

/*
 * A Link-Level Sockaddr may specify the interface in one of two
 * ways: either by means of a system-provided index number (computed
 * anew and possibly differently on every reboot), or by a human-readable
 * string such as "il0" (for managerial convenience).
 *
 * Census taking actions, such as something akin to SIOCGCONF would return
 * both the index and the human name.
 *
 * High volume transactions (such as giving a link-level ``from'' address
 * in a recvfrom or recvmsg call) may be likely only to provide the indexed
 * form, (which requires fewer copy operations and less space).
 *
 * The form and interpretation  of the link-level address is purely a matter
 * of convention between the device driver and its consumers; however, it is
 * expected that all drivers for an interface of a given if_type will agree.
 */

/*
 * Structure of a Link-Level sockaddr:
 */
struct sockaddr_dl {
        u_char  sdl_len;        /* Total length of sockaddr */
        u_char  sdl_family;     /* AF_DLI */
        u_short sdl_index;      /* if != 0, system given index for interface */
        u_char  sdl_type;       /* interface type */
        u_char  sdl_nlen;       /* interface name length, no trailing 0 reqd. */
        u_char  sdl_alen;       /* link level address length */
        u_char  sdl_slen;       /* link layer selector length */
        char    sdl_data[12];   /* minimum work area, can be larger;
                                   contains both if name and ll address */
};

#define LLADDR(s) ((caddr_t)((s)->sdl_data + (s)->sdl_nlen))