4.3BSD-Reno/src/sys/net/if_dl.h

/*
 * Copyright (c) 1990 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution is only permitted until one year after the first shipment
 * of 4.4BSD by the Regents.  Otherwise, redistribution and use in source and
 * binary forms are permitted provided that: (1) source distributions retain
 * this entire copyright notice and comment, and (2) distributions including
 * binaries display the following acknowledgement:  This product includes
 * software developed by the University of California, Berkeley and its
 * contributors'' in the documentation or other materials provided with the
 * distribution and in all advertising materials mentioning features or use
 * of this software.  Neither the name of the University nor the names of
 * its contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *	@(#)if_dl.h	7.1 (Berkeley) 7/1/90
 */

/* 
 * 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))