networking/zcip.c - fp2-dev/platform/external/busybox - Gitiles

 /*
  * 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
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  * General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  * 02111-1307 USA
  */

 /*
  * This can build as part of BusyBox or by itself:
  *
  *	$(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
  *
  * 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 <errno.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <syslog.h>
 #include <poll.h>
 #include <time.h>
 #include <unistd.h>

 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/time.h>
 #include <sys/socket.h>

 #include <arpa/inet.h>
 #include <netinet/in.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>


 static struct arp_packet {
 	struct ether_header hdr;
 	// FIXME this part is netinet/if_ether.h "struct ether_arp"
 	struct arphdr arp;
 	struct ether_addr source_addr;
 	struct in_addr source_ip;
 	struct ether_addr target_addr;
 	struct in_addr target_ip;
 } __attribute__ ((__packed__));

 /* 169.254.0.0 */
 static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;

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

 static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
 static char *prog;

 static const struct in_addr null_ip = { 0 };
 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };

 static int verbose = 0;

 #ifdef DEBUG

 #define DBG(fmt,args...) \
 	fprintf(stderr, "%s: " fmt , prog , ## args)
 #define VDBG(fmt,args...) do { \
 	if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
 	} while (0)
 #else

 #define DBG(fmt,args...) \
 	do { } while (0)
 #define VDBG	DBG
 #endif				/* DEBUG */

 /**
  * 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);
 }

 /**
  * Broadcast an ARP packet.
  */
 static int
 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;

 	// 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.ar_hrd = htons(ARPHRD_ETHER);
 	p.arp.ar_pro = htons(ETHERTYPE_IP);
 	p.arp.ar_hln = ETH_ALEN;
 	p.arp.ar_pln = 4;
 	p.arp.ar_op = htons(op);
 	memcpy(&p.source_addr, source_addr, ETH_ALEN);
 	memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 	memcpy(&p.target_addr, target_addr, ETH_ALEN);
 	memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));

 	// send it
 	if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 		perror("sendto");
 		return -errno;
 	}
 	return 0;
 }

 /**
  * Run a script.
  */
 static int
 run(char *script, char *arg, char *intf, struct in_addr *ip)
 {
 	int pid, status;
 	char *why;

 	if (script != NULL) {
 		VDBG("%s run %s %s\n", intf, script, arg);
 		if (ip != NULL) {
 			char *addr = inet_ntoa(*ip);
 			setenv("ip", addr, 1);
 			syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 		}

 		pid = vfork();
 		if (pid < 0) {			// error
 			why = "vfork";
 			goto bad;
 		} else if (pid == 0) {		// child
 			execl(script, script, arg, NULL);
 			perror("execl");
 			_exit(EXIT_FAILURE);
 		}

 		if (waitpid(pid, &status, 0) <= 0) {
 			why = "waitpid";
 			goto bad;
 		}
 		if (WEXITSTATUS(status) != 0) {
 			fprintf(stderr, "%s: script %s failed, exit=%d\n",
 					prog, script, WEXITSTATUS(status));
 			return -errno;
 		}
 	}
 	return 0;
 bad:
 	status = -errno;
 	syslog(LOG_ERR, "%s %s, %s error: %s",
 		arg, intf, why, strerror(errno));
 	return status;
 }

 #ifndef	NO_BUSYBOX
 #include "busybox.h"
 #endif

 /**
  * Print usage information.
  */
 static void __attribute__((noreturn))
 zcip_usage(const char *msg)
 {
 	fprintf(stderr, "%s: %s\n", prog, msg);
 #ifdef	NO_BUSYBOX
 	fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
 			"\t-f              foreground mode (implied by -v)\n"
 			"\t-q              quit after address (no daemon)\n"
 			"\t-r 169.254.x.x  request this address first\n"
 			"\t-v              verbose; show version\n",
 			prog);
 	exit(0);
 #else
 	bb_show_usage();
 #endif
 }

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

 /**
  * main program
  */

 #ifdef	NO_BUSYBOX
 int
 main(int argc, char *argv[])
 	__attribute__ ((weak, alias ("zcip_main")));
 #endif

 int zcip_main(int argc, char *argv[])
 {
 	char *intf = NULL;
 	char *script = NULL;
 	int quit = 0;
 	int foreground = 0;

 	char *why;
 	struct sockaddr saddr;
 	struct ether_addr addr;
 	struct in_addr ip = { 0 };
 	int fd;
 	int ready = 0;
 	suseconds_t timeout = 0;	// milliseconds
 	time_t defend = 0;
 	unsigned conflicts = 0;
 	unsigned nprobes = 0;
 	unsigned nclaims = 0;
 	int t;

 	// parse commandline: prog [options] ifname script
 	prog = argv[0];
 	while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
 		switch (t) {
 		case 'f':
 			foreground = 1;
 			continue;
 		case 'q':
 			quit = 1;
 			continue;
 		case 'r':
 			if (inet_aton(optarg, &ip) == 0
 					|| (ntohl(ip.s_addr) & IN_CLASSB_NET)
 						!= LINKLOCAL_ADDR) {
 				zcip_usage("invalid link address");
 			}
 			continue;
 		case 'v':
 			if (!verbose)
 				printf("%s: version %s\n", prog, ZCIP_VERSION);
 			verbose++;
 			foreground = 1;
 			continue;
 		default:
 			zcip_usage("bad option");
 		}
 	}
 	if (optind < argc - 1) {
 		intf = argv[optind++];
 		setenv("interface", intf, 1);
 		script = argv[optind++];
 	}
 	if (optind != argc || !intf)
 		zcip_usage("wrong number of arguments");
 	openlog(prog, 0, LOG_DAEMON);

 	// initialize the interface (modprobe, ifup, etc)
 	if (run(script, "init", intf, NULL) < 0)
 		return EXIT_FAILURE;

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

 	// open an ARP socket
 	if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 		why = "open";
 fail:
 		foreground = 1;
 		goto bad;
 	}
 	// bind to the interface's ARP socket
 	if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 		why = "bind";
 		goto fail;
 	} else {
 		struct ifreq ifr;
 		short seed[3];

 		// 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) {
 			why = "get ethernet address";
 			goto fail;
 		}
 		memcpy(&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.
 		memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 		seed48(seed);
 		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 (daemon(0, verbose) < 0) {
 			why = "daemon";
 			goto bad;
 		}
 		syslog(LOG_INFO, "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;

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

 		// poll, being ready to adjust current timeout
 		if (timeout > 0) {
 			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;
 		} else if (timeout == 0) {
 			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.
 		}
 		VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 				timeout, intf, nprobes, nclaims);
 		switch (poll(fds, 1, timeout)) {

 		// timeouts trigger protocol transitions
 		case 0:
 			// probes
 			if (nprobes < PROBE_NUM) {
 				nprobes++;
 				VDBG("probe/%d %s@%s\n",
 						nprobes, intf, inet_ntoa(ip));
 				(void)arp(fd, &saddr, ARPOP_REQUEST,
 						&addr, null_ip,
 						&null_addr, ip);
 				if (nprobes < PROBE_NUM) {
 					timeout = PROBE_MIN * 1000;
 					timeout += ms_rdelay(PROBE_MAX
 							- PROBE_MIN);
 				} else
 					timeout = ANNOUNCE_WAIT * 1000;
 			}
 			// then announcements
 			else if (nclaims < ANNOUNCE_NUM) {
 				nclaims++;
 				VDBG("announce/%d %s@%s\n",
 						nclaims, intf, inet_ntoa(ip));
 				(void)arp(fd, &saddr, ARPOP_REQUEST,
 						&addr, ip,
 						&addr, ip);
 				if (nclaims < ANNOUNCE_NUM) {
 					timeout = ANNOUNCE_INTERVAL * 1000;
 				} else {
 					// link is ok to use earlier
 					run(script, "config", intf, &ip);
 					ready = 1;
 					conflicts = 0;
 					timeout = -1;

 					// NOTE:  all other exit paths
 					// should deconfig ...
 					if (quit)
 						return EXIT_SUCCESS;
 					// FIXME update filters
 				}
 			}
 			break;

 		// packets arriving
 		case 1:
 			// maybe adjust timeout
 			if (timeout > 0) {
 				struct timeval tv2;

 				gettimeofday(&tv2, NULL);
 				if (timercmp(&tv1, &tv2, <)) {
 					timeout = -1;
 				} else {
 					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.
 					fprintf(stderr, "%s %s: poll error\n",
 							prog, intf);
 					if (ready) {
 						run(script, "deconfig",
 								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;

 			VDBG("%s recv arp type=%d, op=%d,\n",
 					intf, ntohs(p.hdr.ether_type),
 					ntohs(p.arp.ar_op));
 			VDBG("\tsource=%s %s\n",
 					ether_ntoa(&p.source_addr),
 					inet_ntoa(p.source_ip));
 			VDBG("\ttarget=%s %s\n",
 					ether_ntoa(&p.target_addr),
 					inet_ntoa(p.target_ip));
 			if (p.arp.ar_op != htons(ARPOP_REQUEST)
 					&& p.arp.ar_op != htons(ARPOP_REPLY))
 				continue;

 			// some cases are always conflicts
 			if ((p.source_ip.s_addr == ip.s_addr)
 					&& (memcmp(&addr, &p.source_addr,
 							ETH_ALEN) != 0)) {
 collision:
 				VDBG("%s ARP conflict from %s\n", intf,
 						ether_ntoa(&p.source_addr));
 				if (ready) {
 					time_t now = time(0);

 					if ((defend + DEFEND_INTERVAL)
 							< now) {
 						defend = now;
 						(void)arp(fd, &saddr,
 								ARPOP_REQUEST,
 								&addr, ip,
 								&addr, ip);
 						VDBG("%s defend\n", intf);
 						timeout = -1;
 						continue;
 					}
 					defend = now;
 					ready = 0;
 					run(script, "deconfig", intf, &ip);
 					// FIXME rm filters: setsockopt(fd,
 					// SO_DETACH_FILTER, ...)
 				}
 				conflicts++;
 				if (conflicts >= MAX_CONFLICTS) {
 					VDBG("%s ratelimit\n", intf);
 					sleep(RATE_LIMIT_INTERVAL);
 				}
 				// restart the whole protocol
 				pick(&ip);
 				timeout = 0;
 				nprobes = 0;
 				nclaims = 0;
 			}
 			// two hosts probing one address is a collision too
 			else if (p.target_ip.s_addr == ip.s_addr
 					&& nclaims == 0
 					&& p.arp.ar_op == htons(ARPOP_REQUEST)
 					&& memcmp(&addr, &p.target_addr,
 							ETH_ALEN) != 0) {
 				goto collision;
 			}
 			break;

 		default:
 			why = "poll";
 			goto bad;
 		}
 	}
 bad:
 	if (foreground)
 		perror(why);
 	else
 		syslog(LOG_ERR, "%s %s, %s error: %s",
 			prog, intf, why, strerror(errno));
 	return EXIT_FAILURE;
 }
	/*
	* 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
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
	* 02111-1307 USA
	*/

	/*
	* This can build as part of BusyBox or by itself:
	*
	* $(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
	*
	* 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 <errno.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <string.h>
	#include <syslog.h>
	#include <poll.h>
	#include <time.h>
	#include <unistd.h>

	#include <sys/ioctl.h>
	#include <sys/types.h>
	#include <sys/wait.h>
	#include <sys/time.h>
	#include <sys/socket.h>

	#include <arpa/inet.h>
	#include <netinet/in.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>


	static struct arp_packet {
	struct ether_header hdr;
	// FIXME this part is netinet/if_ether.h "struct ether_arp"
	struct arphdr arp;
	struct ether_addr source_addr;
	struct in_addr source_ip;
	struct ether_addr target_addr;
	struct in_addr target_ip;
	} __attribute__ ((__packed__));

	/* 169.254.0.0 */
	static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;

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

	static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
	static char *prog;

	static const struct in_addr null_ip = { 0 };
	static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };

	static int verbose = 0;

	#ifdef DEBUG

	#define DBG(fmt,args...) \
	fprintf(stderr, "%s: " fmt , prog , ## args)
	#define VDBG(fmt,args...) do { \
	if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
	} while (0)
	#else

	#define DBG(fmt,args...) \
	do { } while (0)
	#define VDBG DBG
	#endif /* DEBUG */

	/**
	* 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);
	}

	/**
	* Broadcast an ARP packet.
	*/
	static int
	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;

	// 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.ar_hrd = htons(ARPHRD_ETHER);
	p.arp.ar_pro = htons(ETHERTYPE_IP);
	p.arp.ar_hln = ETH_ALEN;
	p.arp.ar_pln = 4;
	p.arp.ar_op = htons(op);
	memcpy(&p.source_addr, source_addr, ETH_ALEN);
	memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
	memcpy(&p.target_addr, target_addr, ETH_ALEN);
	memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));

	// send it
	if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
	perror("sendto");
	return -errno;
	}
	return 0;
	}

	/**
	* Run a script.
	*/
	static int
	run(char script, char arg, char intf, struct in_addr ip)
	{
	int pid, status;
	char *why;

	if (script != NULL) {
	VDBG("%s run %s %s\n", intf, script, arg);
	if (ip != NULL) {
	char addr = inet_ntoa(ip);
	setenv("ip", addr, 1);
	syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
	}

	pid = vfork();
	if (pid < 0) { // error
	why = "vfork";
	goto bad;
	} else if (pid == 0) { // child
	execl(script, script, arg, NULL);
	perror("execl");
	_exit(EXIT_FAILURE);
	}

	if (waitpid(pid, &status, 0) <= 0) {
	why = "waitpid";
	goto bad;
	}
	if (WEXITSTATUS(status) != 0) {
	fprintf(stderr, "%s: script %s failed, exit=%d\n",
	prog, script, WEXITSTATUS(status));
	return -errno;
	}
	}
	return 0;
	bad:
	status = -errno;
	syslog(LOG_ERR, "%s %s, %s error: %s",
	arg, intf, why, strerror(errno));
	return status;
	}

	#ifndef NO_BUSYBOX
	#include "busybox.h"
	#endif

	/**
	* Print usage information.
	*/
	static void __attribute__((noreturn))
	zcip_usage(const char *msg)
	{
	fprintf(stderr, "%s: %s\n", prog, msg);
	#ifdef NO_BUSYBOX
	fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
	"\t-f foreground mode (implied by -v)\n"
	"\t-q quit after address (no daemon)\n"
	"\t-r 169.254.x.x request this address first\n"
	"\t-v verbose; show version\n",
	prog);
	exit(0);
	#else
	bb_show_usage();
	#endif
	}

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

	/**
	* main program
	*/

	#ifdef NO_BUSYBOX
	int
	main(int argc, char *argv[])
	__attribute__ ((weak, alias ("zcip_main")));
	#endif

	int zcip_main(int argc, char *argv[])
	{
	char *intf = NULL;
	char *script = NULL;
	int quit = 0;
	int foreground = 0;

	char *why;
	struct sockaddr saddr;
	struct ether_addr addr;
	struct in_addr ip = { 0 };
	int fd;
	int ready = 0;
	suseconds_t timeout = 0; // milliseconds
	time_t defend = 0;
	unsigned conflicts = 0;
	unsigned nprobes = 0;
	unsigned nclaims = 0;
	int t;

	// parse commandline: prog [options] ifname script
	prog = argv[0];
	while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
	switch (t) {
	case 'f':
	foreground = 1;
	continue;
	case 'q':
	quit = 1;
	continue;
	case 'r':
	if (inet_aton(optarg, &ip) == 0
	\|\| (ntohl(ip.s_addr) & IN_CLASSB_NET)
	!= LINKLOCAL_ADDR) {
	zcip_usage("invalid link address");
	}
	continue;
	case 'v':
	if (!verbose)
	printf("%s: version %s\n", prog, ZCIP_VERSION);
	verbose++;
	foreground = 1;
	continue;
	default:
	zcip_usage("bad option");
	}
	}
	if (optind < argc - 1) {
	intf = argv[optind++];
	setenv("interface", intf, 1);
	script = argv[optind++];
	}
	if (optind != argc \|\| !intf)
	zcip_usage("wrong number of arguments");
	openlog(prog, 0, LOG_DAEMON);

	// initialize the interface (modprobe, ifup, etc)
	if (run(script, "init", intf, NULL) < 0)
	return EXIT_FAILURE;

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

	// open an ARP socket
	if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
	why = "open";
	fail:
	foreground = 1;
	goto bad;
	}
	// bind to the interface's ARP socket
	if (bind(fd, &saddr, sizeof (saddr)) < 0) {
	why = "bind";
	goto fail;
	} else {
	struct ifreq ifr;
	short seed[3];

	// 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) {
	why = "get ethernet address";
	goto fail;
	}
	memcpy(&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.
	memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
	seed48(seed);
	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 (daemon(0, verbose) < 0) {
	why = "daemon";
	goto bad;
	}
	syslog(LOG_INFO, "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;

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

	// poll, being ready to adjust current timeout
	if (timeout > 0) {
	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;
	} else if (timeout == 0) {
	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.
	}
	VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
	timeout, intf, nprobes, nclaims);
	switch (poll(fds, 1, timeout)) {

	// timeouts trigger protocol transitions
	case 0:
	// probes
	if (nprobes < PROBE_NUM) {
	nprobes++;
	VDBG("probe/%d %s@%s\n",
	nprobes, intf, inet_ntoa(ip));
	(void)arp(fd, &saddr, ARPOP_REQUEST,
	&addr, null_ip,
	&null_addr, ip);
	if (nprobes < PROBE_NUM) {
	timeout = PROBE_MIN * 1000;
	timeout += ms_rdelay(PROBE_MAX
	- PROBE_MIN);
	} else
	timeout = ANNOUNCE_WAIT * 1000;
	}
	// then announcements
	else if (nclaims < ANNOUNCE_NUM) {
	nclaims++;
	VDBG("announce/%d %s@%s\n",
	nclaims, intf, inet_ntoa(ip));
	(void)arp(fd, &saddr, ARPOP_REQUEST,
	&addr, ip,
	&addr, ip);
	if (nclaims < ANNOUNCE_NUM) {
	timeout = ANNOUNCE_INTERVAL * 1000;
	} else {
	// link is ok to use earlier
	run(script, "config", intf, &ip);
	ready = 1;
	conflicts = 0;
	timeout = -1;

	// NOTE: all other exit paths
	// should deconfig ...
	if (quit)
	return EXIT_SUCCESS;
	// FIXME update filters
	}
	}
	break;

	// packets arriving
	case 1:
	// maybe adjust timeout
	if (timeout > 0) {
	struct timeval tv2;

	gettimeofday(&tv2, NULL);
	if (timercmp(&tv1, &tv2, <)) {
	timeout = -1;
	} else {
	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.
	fprintf(stderr, "%s %s: poll error\n",
	prog, intf);
	if (ready) {
	run(script, "deconfig",
	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;

	VDBG("%s recv arp type=%d, op=%d,\n",
	intf, ntohs(p.hdr.ether_type),
	ntohs(p.arp.ar_op));
	VDBG("\tsource=%s %s\n",
	ether_ntoa(&p.source_addr),
	inet_ntoa(p.source_ip));
	VDBG("\ttarget=%s %s\n",
	ether_ntoa(&p.target_addr),
	inet_ntoa(p.target_ip));
	if (p.arp.ar_op != htons(ARPOP_REQUEST)
	&& p.arp.ar_op != htons(ARPOP_REPLY))
	continue;

	// some cases are always conflicts
	if ((p.source_ip.s_addr == ip.s_addr)
	&& (memcmp(&addr, &p.source_addr,
	ETH_ALEN) != 0)) {
	collision:
	VDBG("%s ARP conflict from %s\n", intf,
	ether_ntoa(&p.source_addr));
	if (ready) {
	time_t now = time(0);

	if ((defend + DEFEND_INTERVAL)
	< now) {
	defend = now;
	(void)arp(fd, &saddr,
	ARPOP_REQUEST,
	&addr, ip,
	&addr, ip);
	VDBG("%s defend\n", intf);
	timeout = -1;
	continue;
	}
	defend = now;
	ready = 0;
	run(script, "deconfig", intf, &ip);
	// FIXME rm filters: setsockopt(fd,
	// SO_DETACH_FILTER, ...)
	}
	conflicts++;
	if (conflicts >= MAX_CONFLICTS) {
	VDBG("%s ratelimit\n", intf);
	sleep(RATE_LIMIT_INTERVAL);
	}
	// restart the whole protocol
	pick(&ip);
	timeout = 0;
	nprobes = 0;
	nclaims = 0;
	}
	// two hosts probing one address is a collision too
	else if (p.target_ip.s_addr == ip.s_addr
	&& nclaims == 0
	&& p.arp.ar_op == htons(ARPOP_REQUEST)
	&& memcmp(&addr, &p.target_addr,
	ETH_ALEN) != 0) {
	goto collision;
	}
	break;

	default:
	why = "poll";
	goto bad;
	}
	}
	bad:
	if (foreground)
	perror(why);
	else
	syslog(LOG_ERR, "%s %s, %s error: %s",
	prog, intf, why, strerror(errno));
	return EXIT_FAILURE;
	}