networking/zcip.c - codeaurora/busybox - Gitiles

 /* vi: set sw=4 ts=4: */
 /*
  * RFC3927 ZeroConf IPv4 Link-Local addressing
  * (see <http://www.zeroconf.org/>)
  *
  * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
  * Copyright (C) 2004 by David Brownell
  *
  * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
  */

 /*
  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  * routed at the IP level, though various proxies or bridges can
  * certainly be used.  Its naming is built over multicast DNS.
  */

 //#define DEBUG

 // TODO:
 // - more real-world usage/testing, especially daemon mode
 // - kernel packet filters to reduce scheduling noise
 // - avoid silent script failures, especially under load...
 // - link status monitoring (restart on link-up; stop on link-down)

 #include "busybox.h"
 #include <syslog.h>
 #include <poll.h>
 #include <sys/wait.h>
 #include <netinet/ether.h>
 #include <net/ethernet.h>
 #include <net/if.h>
 #include <net/if_arp.h>

 #include <linux/if_packet.h>
 #include <linux/sockios.h>


 struct arp_packet {
 	struct ether_header hdr;
 	struct ether_arp arp;
 } ATTRIBUTE_PACKED;

 enum {
 /* 169.254.0.0 */
 	LINKLOCAL_ADDR = 0xa9fe0000,

 /* protocol timeout parameters, specified in seconds */
 	PROBE_WAIT = 1,
 	PROBE_MIN = 1,
 	PROBE_MAX = 2,
 	PROBE_NUM = 3,
 	MAX_CONFLICTS = 10,
 	RATE_LIMIT_INTERVAL = 60,
 	ANNOUNCE_WAIT = 2,
 	ANNOUNCE_NUM = 2,
 	ANNOUNCE_INTERVAL = 2,
 	DEFEND_INTERVAL = 10
 };

 /* States during the configuration process. */
 enum {
 	PROBE = 0,
 	RATE_LIMIT_PROBE,
 	ANNOUNCE,
 	MONITOR,
 	DEFEND
 };

 #define VDBG(fmt,args...) \
 	do { } while (0)

 /**
  * Pick a random link local IP address on 169.254/16, except that
  * the first and last 256 addresses are reserved.
  */
 static void pick(struct in_addr *ip)
 {
 	unsigned tmp;

 	/* use cheaper math than lrand48() mod N */
 	do {
 		tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 	} while (tmp > (IN_CLASSB_HOST - 0x0200));
 	ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 }

 /* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */

 /**
  * Broadcast an ARP packet.
  */
 static void arp(int fd, struct sockaddr *saddr, int op,
 	const struct ether_addr *source_addr, struct in_addr source_ip,
 	const struct ether_addr *target_addr, struct in_addr target_ip)
 {
 	struct arp_packet p;
 	memset(&p, 0, sizeof(p));

 	// ether header
 	p.hdr.ether_type = htons(ETHERTYPE_ARP);
 	memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 	memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);

 	// arp request
 	p.arp.arp_hrd = htons(ARPHRD_ETHER);
 	p.arp.arp_pro = htons(ETHERTYPE_IP);
 	p.arp.arp_hln = ETH_ALEN;
 	p.arp.arp_pln = 4;
 	p.arp.arp_op = htons(op);
 	memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
 	memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
 	memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
 	memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));

 	// send it
 	if (sendto(fd, &p, sizeof(p), 0, saddr, sizeof(*saddr)) < 0) {
 		bb_perror_msg("sendto");
 		//return -errno;
 	}
 	// Currently all callers ignore errors, that's why returns are
 	// commented out...
 	//return 0;
 }

 /**
  * Run a script. argv[2] is already NULL.
  */
 static int run(char *argv[3], const char *intf, struct in_addr *ip)
 {
 	int status;

 	VDBG("%s run %s %s\n", intf, argv[0], argv[1]);

 	if (ip) {
 		char *addr = inet_ntoa(*ip);
 		setenv("ip", addr, 1);
 		bb_info_msg("%s %s %s", argv[1], intf, addr);
 	}

 	status = wait4pid(spawn(argv));
 	if (status < 0) {
 		bb_perror_msg("%s %s", argv[1], intf);
 		return -errno;
 	}
 	if (status != 0)
 		bb_error_msg("script %s %s failed, exitcode=%d", argv[0], argv[1], status);
 	return status;
 }

 /**
  * Return milliseconds of random delay, up to "secs" seconds.
  */
 static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
 {
 	return lrand48() % (secs * 1000);
 }

 /**
  * main program
  */
 int zcip_main(int argc, char **argv);
 int zcip_main(int argc, char **argv)
 {
 	int state = PROBE;
 	struct ether_addr eth_addr;
 	const char *why;
 	int fd;
 	char *r_opt;
 	unsigned opts;

 	/* Ugly trick, but I want these zeroed in one go */
 	struct {
 		const struct in_addr null_ip;
 		const struct ether_addr null_addr;
 		struct sockaddr saddr;
 		struct in_addr ip;
 		struct ifreq ifr;
 		char *intf;
 		char *script_av[3];
 		suseconds_t timeout; // milliseconds
 		unsigned conflicts;
 		unsigned nprobes;
 		unsigned nclaims;
 		int ready;
 		int verbose;
 	} L;
 #define null_ip   (L.null_ip  )
 #define null_addr (L.null_addr)
 #define saddr     (L.saddr    )
 #define ip        (L.ip       )
 #define ifr       (L.ifr      )
 #define intf      (L.intf     )
 #define script_av (L.script_av)
 #define timeout   (L.timeout  )
 #define conflicts (L.conflicts)
 #define nprobes   (L.nprobes  )
 #define nclaims   (L.nclaims  )
 #define ready     (L.ready    )
 #define verbose   (L.verbose  )

 	memset(&L, 0, sizeof(L));

 #define FOREGROUND (opts & 1)
 #define QUIT       (opts & 2)
 	// parse commandline: prog [options] ifname script
 	// exactly 2 args; -v accumulates and implies -f
 	opt_complementary = "=2:vv:vf";
 	opts = getopt32(argc, argv, "fqr:v", &r_opt, &verbose);
 	if (!FOREGROUND) {
 		/* Do it early, before all bb_xx_msg calls */
 		openlog(applet_name, 0, LOG_DAEMON);
 		logmode |= LOGMODE_SYSLOG;
 	}
 	if (opts & 4) { // -r n.n.n.n
 		if (inet_aton(r_opt, &ip) == 0
 		 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
 		) {
 			bb_error_msg_and_die("invalid link address");
 		}
 	}
 	// On NOMMU reexec early (or else we will rerun things twice)
 #if !BB_MMU
 	if (!FOREGROUND)
 		bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
 #endif
 	argc -= optind;
 	argv += optind;

 	intf = argv[0];
 	script_av[0] = argv[1];
 	setenv("interface", intf, 1);

 	// initialize the interface (modprobe, ifup, etc)
 	script_av[1] = (char*)"init";
 	if (run(script_av, intf, NULL))
 		return EXIT_FAILURE;

 	// initialize saddr
 	//memset(&saddr, 0, sizeof(saddr));
 	safe_strncpy(saddr.sa_data, intf, sizeof(saddr.sa_data));

 	// open an ARP socket
 	fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
 	// bind to the interface's ARP socket
 	xbind(fd, &saddr, sizeof(saddr));

 	// get the interface's ethernet address
 	//memset(&ifr, 0, sizeof(ifr));
 	strncpy(ifr.ifr_name, intf, sizeof(ifr.ifr_name));
 	if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 		bb_perror_msg_and_die("get ethernet address");
 	}
 	memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);

 	// start with some stable ip address, either a function of
 	// the hardware address or else the last address we used.
 	// NOTE: the sequence of addresses we try changes only
 	// depending on when we detect conflicts.
 	// (SVID 3 bogon: who says that "short" is always 16 bits?)
 	seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data );
 	if (ip.s_addr == 0)
 		pick(&ip);

 	// FIXME cases to handle:
 	//  - zcip already running!
 	//  - link already has local address... just defend/update

 	// daemonize now; don't delay system startup
 	if (!FOREGROUND) {
 #if BB_MMU
 		bb_daemonize(DAEMON_CHDIR_ROOT);
 #endif
 		bb_info_msg("start, interface %s", intf);
 	}

 	// run the dynamic address negotiation protocol,
 	// restarting after address conflicts:
 	//  - start with some address we want to try
 	//  - short random delay
 	//  - arp probes to see if another host else uses it
 	//  - arp announcements that we're claiming it
 	//  - use it
 	//  - defend it, within limits
 	while (1) {
 		struct pollfd fds[1];
 		struct timeval tv1;
 		struct arp_packet p;

 		int source_ip_conflict = 0;
 		int target_ip_conflict = 0;

 		fds[0].fd = fd;
 		fds[0].events = POLLIN;
 		fds[0].revents = 0;

 		// poll, being ready to adjust current timeout
 		if (!timeout) {
 			timeout = ms_rdelay(PROBE_WAIT);
 			// FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 			// make the kernel filter out all packets except
 			// ones we'd care about.
 		}
 		// set tv1 to the point in time when we timeout
 		gettimeofday(&tv1, NULL);
 		tv1.tv_usec += (timeout % 1000) * 1000;
 		while (tv1.tv_usec > 1000000) {
 			tv1.tv_usec -= 1000000;
 			tv1.tv_sec++;
 		}
 		tv1.tv_sec += timeout / 1000;

 		VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 				timeout, intf, nprobes, nclaims);
 		switch (poll(fds, 1, timeout)) {

 		// timeout
 		case 0:
 			VDBG("state = %d\n", state);
 			switch (state) {
 			case PROBE:
 				// timeouts in the PROBE state mean no conflicting ARP packets
 				// have been received, so we can progress through the states
 				if (nprobes < PROBE_NUM) {
 					nprobes++;
 					VDBG("probe/%d %s@%s\n",
 							nprobes, intf, inet_ntoa(ip));
 					arp(fd, &saddr, ARPOP_REQUEST,
 							&eth_addr, null_ip,
 							&null_addr, ip);
 					timeout = PROBE_MIN * 1000;
 					timeout += ms_rdelay(PROBE_MAX
 							- PROBE_MIN);
 				}
 				else {
 					// Switch to announce state.
 					state = ANNOUNCE;
 					nclaims = 0;
 					VDBG("announce/%d %s@%s\n",
 							nclaims, intf, inet_ntoa(ip));
 					arp(fd, &saddr, ARPOP_REQUEST,
 							&eth_addr, ip,
 							&eth_addr, ip);
 					timeout = ANNOUNCE_INTERVAL * 1000;
 				}
 				break;
 			case RATE_LIMIT_PROBE:
 				// timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
 				// have been received, so we can move immediately to the announce state
 				state = ANNOUNCE;
 				nclaims = 0;
 				VDBG("announce/%d %s@%s\n",
 						nclaims, intf, inet_ntoa(ip));
 				arp(fd, &saddr, ARPOP_REQUEST,
 						&eth_addr, ip,
 						&eth_addr, ip);
 				timeout = ANNOUNCE_INTERVAL * 1000;
 				break;
 			case ANNOUNCE:
 				// timeouts in the ANNOUNCE state mean no conflicting ARP packets
 				// have been received, so we can progress through the states
 				if (nclaims < ANNOUNCE_NUM) {
 					nclaims++;
 					VDBG("announce/%d %s@%s\n",
 							nclaims, intf, inet_ntoa(ip));
 					arp(fd, &saddr, ARPOP_REQUEST,
 							&eth_addr, ip,
 							&eth_addr, ip);
 					timeout = ANNOUNCE_INTERVAL * 1000;
 				}
 				else {
 					// Switch to monitor state.
 					state = MONITOR;
 					// link is ok to use earlier
 					// FIXME update filters
 					script_av[1] = (char*)"config";
 					run(script_av, intf, &ip);
 					ready = 1;
 					conflicts = 0;
 					timeout = -1; // Never timeout in the monitor state.

 					// NOTE: all other exit paths
 					// should deconfig ...
 					if (QUIT)
 						return EXIT_SUCCESS;
 				}
 				break;
 			case DEFEND:
 				// We won!  No ARP replies, so just go back to monitor.
 				state = MONITOR;
 				timeout = -1;
 				conflicts = 0;
 				break;
 			default:
 				// Invalid, should never happen.  Restart the whole protocol.
 				state = PROBE;
 				pick(&ip);
 				timeout = 0;
 				nprobes = 0;
 				nclaims = 0;
 				break;
 			} // switch (state)
 			break; // case 0 (timeout)
 		// packets arriving
 		case 1:
 			// We need to adjust the timeout in case we didn't receive
 			// a conflicting packet.
 			if (timeout > 0) {
 				struct timeval tv2;

 				gettimeofday(&tv2, NULL);
 				if (timercmp(&tv1, &tv2, <)) {
 					// Current time is greater than the expected timeout time.
 					// Should never happen.
 					VDBG("missed an expected timeout\n");
 					timeout = 0;
 				} else {
 					VDBG("adjusting timeout\n");
 					timersub(&tv1, &tv2, &tv1);
 					timeout = 1000 * tv1.tv_sec
 							+ tv1.tv_usec / 1000;
 				}
 			}

 			if ((fds[0].revents & POLLIN) == 0) {
 				if (fds[0].revents & POLLERR) {
 					// FIXME: links routinely go down;
 					// this shouldn't necessarily exit.
 					bb_error_msg("%s: poll error", intf);
 					if (ready) {
 						script_av[1] = (char*)"deconfig";
 						run(script_av, intf, &ip);
 					}
 					return EXIT_FAILURE;
 				}
 				continue;
 			}

 			// read ARP packet
 			if (recv(fd, &p, sizeof(p), 0) < 0) {
 				why = "recv";
 				goto bad;
 			}
 			if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 				continue;

 #ifdef DEBUG
 			{
 				struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
 				struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
 				struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
 				struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
 				VDBG("%s recv arp type=%d, op=%d,\n",
 					intf, ntohs(p.hdr.ether_type),
 					ntohs(p.arp.arp_op));
 				VDBG("\tsource=%s %s\n",
 					ether_ntoa(sha),
 					inet_ntoa(*spa));
 				VDBG("\ttarget=%s %s\n",
 					ether_ntoa(tha),
 					inet_ntoa(*tpa));
 			}
 #endif
 			if (p.arp.arp_op != htons(ARPOP_REQUEST)
 					&& p.arp.arp_op != htons(ARPOP_REPLY))
 				continue;

 			if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
 				memcmp(&eth_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
 				source_ip_conflict = 1;
 			}
 			if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
 				p.arp.arp_op == htons(ARPOP_REQUEST) &&
 				memcmp(&eth_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
 				target_ip_conflict = 1;
 			}

 			VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
 				state, source_ip_conflict, target_ip_conflict);
 			switch (state) {
 			case PROBE:
 			case ANNOUNCE:
 				// When probing or announcing, check for source IP conflicts
 				// and other hosts doing ARP probes (target IP conflicts).
 				if (source_ip_conflict || target_ip_conflict) {
 					conflicts++;
 					if (conflicts >= MAX_CONFLICTS) {
 						VDBG("%s ratelimit\n", intf);
 						timeout = RATE_LIMIT_INTERVAL * 1000;
 						state = RATE_LIMIT_PROBE;
 					}

 					// restart the whole protocol
 					pick(&ip);
 					timeout = 0;
 					nprobes = 0;
 					nclaims = 0;
 				}
 				break;
 			case MONITOR:
 				// If a conflict, we try to defend with a single ARP probe.
 				if (source_ip_conflict) {
 					VDBG("monitor conflict -- defending\n");
 					state = DEFEND;
 					timeout = DEFEND_INTERVAL * 1000;
 					arp(fd, &saddr,
 							ARPOP_REQUEST,
 							&eth_addr, ip,
 							&eth_addr, ip);
 				}
 				break;
 			case DEFEND:
 				// Well, we tried.  Start over (on conflict).
 				if (source_ip_conflict) {
 					state = PROBE;
 					VDBG("defend conflict -- starting over\n");
 					ready = 0;
 					script_av[1] = (char*)"deconfig";
 					run(script_av, intf, &ip);

 					// restart the whole protocol
 					pick(&ip);
 					timeout = 0;
 					nprobes = 0;
 					nclaims = 0;
 				}
 				break;
 			default:
 				// Invalid, should never happen.  Restart the whole protocol.
 				VDBG("invalid state -- starting over\n");
 				state = PROBE;
 				pick(&ip);
 				timeout = 0;
 				nprobes = 0;
 				nclaims = 0;
 				break;
 			} // switch state

 			break; // case 1 (packets arriving)
 		default:
 			why = "poll";
 			goto bad;
 		} // switch poll
 	}
  bad:
 	bb_perror_msg("%s, %s", intf, why);
 	return EXIT_FAILURE;
 }
	/* vi: set sw=4 ts=4: */
	/*
	* RFC3927 ZeroConf IPv4 Link-Local addressing
	* (see <http://www.zeroconf.org/>)
	*
	* Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
	* Copyright (C) 2004 by David Brownell
	*
	* Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
	*/

	/*
	* ZCIP just manages the 169.254.. addresses. That network is not
	* routed at the IP level, though various proxies or bridges can
	* certainly be used. Its naming is built over multicast DNS.
	*/

	//#define DEBUG

	// TODO:
	// - more real-world usage/testing, especially daemon mode
	// - kernel packet filters to reduce scheduling noise
	// - avoid silent script failures, especially under load...
	// - link status monitoring (restart on link-up; stop on link-down)

	#include "busybox.h"
	#include <syslog.h>
	#include <poll.h>
	#include <sys/wait.h>
	#include <netinet/ether.h>
	#include <net/ethernet.h>
	#include <net/if.h>
	#include <net/if_arp.h>

	#include <linux/if_packet.h>
	#include <linux/sockios.h>


	struct arp_packet {
	struct ether_header hdr;
	struct ether_arp arp;
	} ATTRIBUTE_PACKED;

	enum {
	/* 169.254.0.0 */
	LINKLOCAL_ADDR = 0xa9fe0000,

	/* protocol timeout parameters, specified in seconds */
	PROBE_WAIT = 1,
	PROBE_MIN = 1,
	PROBE_MAX = 2,
	PROBE_NUM = 3,
	MAX_CONFLICTS = 10,
	RATE_LIMIT_INTERVAL = 60,
	ANNOUNCE_WAIT = 2,
	ANNOUNCE_NUM = 2,
	ANNOUNCE_INTERVAL = 2,
	DEFEND_INTERVAL = 10
	};

	/* States during the configuration process. */
	enum {
	PROBE = 0,
	RATE_LIMIT_PROBE,
	ANNOUNCE,
	MONITOR,
	DEFEND
	};

	#define VDBG(fmt,args...) \
	do { } while (0)

	/**
	* Pick a random link local IP address on 169.254/16, except that
	* the first and last 256 addresses are reserved.
	*/
	static void pick(struct in_addr *ip)
	{
	unsigned tmp;

	/* use cheaper math than lrand48() mod N */
	do {
	tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
	} while (tmp > (IN_CLASSB_HOST - 0x0200));
	ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
	}

	/* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */

	/**
	* Broadcast an ARP packet.
	*/
	static void arp(int fd, struct sockaddr *saddr, int op,
	const struct ether_addr *source_addr, struct in_addr source_ip,
	const struct ether_addr *target_addr, struct in_addr target_ip)
	{
	struct arp_packet p;
	memset(&p, 0, sizeof(p));

	// ether header
	p.hdr.ether_type = htons(ETHERTYPE_ARP);
	memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
	memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);

	// arp request
	p.arp.arp_hrd = htons(ARPHRD_ETHER);
	p.arp.arp_pro = htons(ETHERTYPE_IP);
	p.arp.arp_hln = ETH_ALEN;
	p.arp.arp_pln = 4;
	p.arp.arp_op = htons(op);
	memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
	memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
	memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
	memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));

	// send it
	if (sendto(fd, &p, sizeof(p), 0, saddr, sizeof(*saddr)) < 0) {
	bb_perror_msg("sendto");
	//return -errno;
	}
	// Currently all callers ignore errors, that's why returns are
	// commented out...
	//return 0;
	}

	/**
	* Run a script. argv[2] is already NULL.
	*/
	static int run(char argv[3], const char intf, struct in_addr *ip)
	{
	int status;

	VDBG("%s run %s %s\n", intf, argv[0], argv[1]);

	if (ip) {
	char addr = inet_ntoa(ip);
	setenv("ip", addr, 1);
	bb_info_msg("%s %s %s", argv[1], intf, addr);
	}

	status = wait4pid(spawn(argv));
	if (status < 0) {
	bb_perror_msg("%s %s", argv[1], intf);
	return -errno;
	}
	if (status != 0)
	bb_error_msg("script %s %s failed, exitcode=%d", argv[0], argv[1], status);
	return status;
	}

	/**
	* Return milliseconds of random delay, up to "secs" seconds.
	*/
	static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
	{
	return lrand48() % (secs * 1000);
	}

	/**
	* main program
	*/
	int zcip_main(int argc, char **argv);
	int zcip_main(int argc, char **argv)
	{
	int state = PROBE;
	struct ether_addr eth_addr;
	const char *why;
	int fd;
	char *r_opt;
	unsigned opts;

	/* Ugly trick, but I want these zeroed in one go */
	struct {
	const struct in_addr null_ip;
	const struct ether_addr null_addr;
	struct sockaddr saddr;
	struct in_addr ip;
	struct ifreq ifr;
	char *intf;
	char *script_av[3];
	suseconds_t timeout; // milliseconds
	unsigned conflicts;
	unsigned nprobes;
	unsigned nclaims;
	int ready;
	int verbose;
	} L;
	#define null_ip (L.null_ip )
	#define null_addr (L.null_addr)
	#define saddr (L.saddr )
	#define ip (L.ip )
	#define ifr (L.ifr )
	#define intf (L.intf )
	#define script_av (L.script_av)
	#define timeout (L.timeout )
	#define conflicts (L.conflicts)
	#define nprobes (L.nprobes )
	#define nclaims (L.nclaims )
	#define ready (L.ready )
	#define verbose (L.verbose )

	memset(&L, 0, sizeof(L));

	#define FOREGROUND (opts & 1)
	#define QUIT (opts & 2)
	// parse commandline: prog [options] ifname script
	// exactly 2 args; -v accumulates and implies -f
	opt_complementary = "=2:vv:vf";
	opts = getopt32(argc, argv, "fqr:v", &r_opt, &verbose);
	if (!FOREGROUND) {
	/* Do it early, before all bb_xx_msg calls */
	openlog(applet_name, 0, LOG_DAEMON);
	logmode \|= LOGMODE_SYSLOG;
	}
	if (opts & 4) { // -r n.n.n.n
	if (inet_aton(r_opt, &ip) == 0
	\|\| (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
	) {
	bb_error_msg_and_die("invalid link address");
	}
	}
	// On NOMMU reexec early (or else we will rerun things twice)
	#if !BB_MMU
	if (!FOREGROUND)
	bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
	#endif
	argc -= optind;
	argv += optind;

	intf = argv[0];
	script_av[0] = argv[1];
	setenv("interface", intf, 1);

	// initialize the interface (modprobe, ifup, etc)
	script_av[1] = (char*)"init";
	if (run(script_av, intf, NULL))
	return EXIT_FAILURE;

	// initialize saddr
	//memset(&saddr, 0, sizeof(saddr));
	safe_strncpy(saddr.sa_data, intf, sizeof(saddr.sa_data));

	// open an ARP socket
	fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
	// bind to the interface's ARP socket
	xbind(fd, &saddr, sizeof(saddr));

	// get the interface's ethernet address
	//memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, intf, sizeof(ifr.ifr_name));
	if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
	bb_perror_msg_and_die("get ethernet address");
	}
	memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);

	// start with some stable ip address, either a function of
	// the hardware address or else the last address we used.
	// NOTE: the sequence of addresses we try changes only
	// depending on when we detect conflicts.
	// (SVID 3 bogon: who says that "short" is always 16 bits?)
	seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data );
	if (ip.s_addr == 0)
	pick(&ip);

	// FIXME cases to handle:
	// - zcip already running!
	// - link already has local address... just defend/update

	// daemonize now; don't delay system startup
	if (!FOREGROUND) {
	#if BB_MMU
	bb_daemonize(DAEMON_CHDIR_ROOT);
	#endif
	bb_info_msg("start, interface %s", intf);
	}

	// run the dynamic address negotiation protocol,
	// restarting after address conflicts:
	// - start with some address we want to try
	// - short random delay
	// - arp probes to see if another host else uses it
	// - arp announcements that we're claiming it
	// - use it
	// - defend it, within limits
	while (1) {
	struct pollfd fds[1];
	struct timeval tv1;
	struct arp_packet p;

	int source_ip_conflict = 0;
	int target_ip_conflict = 0;

	fds[0].fd = fd;
	fds[0].events = POLLIN;
	fds[0].revents = 0;

	// poll, being ready to adjust current timeout
	if (!timeout) {
	timeout = ms_rdelay(PROBE_WAIT);
	// FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
	// make the kernel filter out all packets except
	// ones we'd care about.
	}
	// set tv1 to the point in time when we timeout
	gettimeofday(&tv1, NULL);
	tv1.tv_usec += (timeout % 1000) * 1000;
	while (tv1.tv_usec > 1000000) {
	tv1.tv_usec -= 1000000;
	tv1.tv_sec++;
	}
	tv1.tv_sec += timeout / 1000;

	VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
	timeout, intf, nprobes, nclaims);
	switch (poll(fds, 1, timeout)) {

	// timeout
	case 0:
	VDBG("state = %d\n", state);
	switch (state) {
	case PROBE:
	// timeouts in the PROBE state mean no conflicting ARP packets
	// have been received, so we can progress through the states
	if (nprobes < PROBE_NUM) {
	nprobes++;
	VDBG("probe/%d %s@%s\n",
	nprobes, intf, inet_ntoa(ip));
	arp(fd, &saddr, ARPOP_REQUEST,
	&eth_addr, null_ip,
	&null_addr, ip);
	timeout = PROBE_MIN * 1000;
	timeout += ms_rdelay(PROBE_MAX
	- PROBE_MIN);
	}
	else {
	// Switch to announce state.
	state = ANNOUNCE;
	nclaims = 0;
	VDBG("announce/%d %s@%s\n",
	nclaims, intf, inet_ntoa(ip));
	arp(fd, &saddr, ARPOP_REQUEST,
	&eth_addr, ip,
	&eth_addr, ip);
	timeout = ANNOUNCE_INTERVAL * 1000;
	}
	break;
	case RATE_LIMIT_PROBE:
	// timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
	// have been received, so we can move immediately to the announce state
	state = ANNOUNCE;
	nclaims = 0;
	VDBG("announce/%d %s@%s\n",
	nclaims, intf, inet_ntoa(ip));
	arp(fd, &saddr, ARPOP_REQUEST,
	&eth_addr, ip,
	&eth_addr, ip);
	timeout = ANNOUNCE_INTERVAL * 1000;
	break;
	case ANNOUNCE:
	// timeouts in the ANNOUNCE state mean no conflicting ARP packets
	// have been received, so we can progress through the states
	if (nclaims < ANNOUNCE_NUM) {
	nclaims++;
	VDBG("announce/%d %s@%s\n",
	nclaims, intf, inet_ntoa(ip));
	arp(fd, &saddr, ARPOP_REQUEST,
	&eth_addr, ip,
	&eth_addr, ip);
	timeout = ANNOUNCE_INTERVAL * 1000;
	}
	else {
	// Switch to monitor state.
	state = MONITOR;
	// link is ok to use earlier
	// FIXME update filters
	script_av[1] = (char*)"config";
	run(script_av, intf, &ip);
	ready = 1;
	conflicts = 0;
	timeout = -1; // Never timeout in the monitor state.

	// NOTE: all other exit paths
	// should deconfig ...
	if (QUIT)
	return EXIT_SUCCESS;
	}
	break;
	case DEFEND:
	// We won! No ARP replies, so just go back to monitor.
	state = MONITOR;
	timeout = -1;
	conflicts = 0;
	break;
	default:
	// Invalid, should never happen. Restart the whole protocol.
	state = PROBE;
	pick(&ip);
	timeout = 0;
	nprobes = 0;
	nclaims = 0;
	break;
	} // switch (state)
	break; // case 0 (timeout)
	// packets arriving
	case 1:
	// We need to adjust the timeout in case we didn't receive
	// a conflicting packet.
	if (timeout > 0) {
	struct timeval tv2;

	gettimeofday(&tv2, NULL);
	if (timercmp(&tv1, &tv2, <)) {
	// Current time is greater than the expected timeout time.
	// Should never happen.
	VDBG("missed an expected timeout\n");
	timeout = 0;
	} else {
	VDBG("adjusting timeout\n");
	timersub(&tv1, &tv2, &tv1);
	timeout = 1000 * tv1.tv_sec
	+ tv1.tv_usec / 1000;
	}
	}

	if ((fds[0].revents & POLLIN) == 0) {
	if (fds[0].revents & POLLERR) {
	// FIXME: links routinely go down;
	// this shouldn't necessarily exit.
	bb_error_msg("%s: poll error", intf);
	if (ready) {
	script_av[1] = (char*)"deconfig";
	run(script_av, intf, &ip);
	}
	return EXIT_FAILURE;
	}
	continue;
	}

	// read ARP packet
	if (recv(fd, &p, sizeof(p), 0) < 0) {
	why = "recv";
	goto bad;
	}
	if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
	continue;

	#ifdef DEBUG
	{
	struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
	struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
	struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
	struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
	VDBG("%s recv arp type=%d, op=%d,\n",
	intf, ntohs(p.hdr.ether_type),
	ntohs(p.arp.arp_op));
	VDBG("\tsource=%s %s\n",
	ether_ntoa(sha),
	inet_ntoa(*spa));
	VDBG("\ttarget=%s %s\n",
	ether_ntoa(tha),
	inet_ntoa(*tpa));
	}
	#endif
	if (p.arp.arp_op != htons(ARPOP_REQUEST)
	&& p.arp.arp_op != htons(ARPOP_REPLY))
	continue;

	if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
	memcmp(&eth_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
	source_ip_conflict = 1;
	}
	if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
	p.arp.arp_op == htons(ARPOP_REQUEST) &&
	memcmp(&eth_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
	target_ip_conflict = 1;
	}

	VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
	state, source_ip_conflict, target_ip_conflict);
	switch (state) {
	case PROBE:
	case ANNOUNCE:
	// When probing or announcing, check for source IP conflicts
	// and other hosts doing ARP probes (target IP conflicts).
	if (source_ip_conflict \|\| target_ip_conflict) {
	conflicts++;
	if (conflicts >= MAX_CONFLICTS) {
	VDBG("%s ratelimit\n", intf);
	timeout = RATE_LIMIT_INTERVAL * 1000;
	state = RATE_LIMIT_PROBE;
	}

	// restart the whole protocol
	pick(&ip);
	timeout = 0;
	nprobes = 0;
	nclaims = 0;
	}
	break;
	case MONITOR:
	// If a conflict, we try to defend with a single ARP probe.
	if (source_ip_conflict) {
	VDBG("monitor conflict -- defending\n");
	state = DEFEND;
	timeout = DEFEND_INTERVAL * 1000;
	arp(fd, &saddr,
	ARPOP_REQUEST,
	&eth_addr, ip,
	&eth_addr, ip);
	}
	break;
	case DEFEND:
	// Well, we tried. Start over (on conflict).
	if (source_ip_conflict) {
	state = PROBE;
	VDBG("defend conflict -- starting over\n");
	ready = 0;
	script_av[1] = (char*)"deconfig";
	run(script_av, intf, &ip);

	// restart the whole protocol
	pick(&ip);
	timeout = 0;
	nprobes = 0;
	nclaims = 0;
	}
	break;
	default:
	// Invalid, should never happen. Restart the whole protocol.
	VDBG("invalid state -- starting over\n");
	state = PROBE;
	pick(&ip);
	timeout = 0;
	nprobes = 0;
	nclaims = 0;
	break;
	} // switch state

	break; // case 1 (packets arriving)
	default:
	why = "poll";
	goto bad;
	} // switch poll
	}
	bad:
	bb_perror_msg("%s, %s", intf, why);
	return EXIT_FAILURE;
	}