plan9fox/sys/src/cmd/ip/dhcpd/dhcpd.c

#include <u.h>
#include <libc.h>
#include <ip.h>
#include <bio.h>
#include <ndb.h>
#include "dat.h"

/*
 *	ala rfc2131
 */

enum {
	Maxloglen = 1024,
};

typedef struct Req Req;
struct Req
{
	int	fd;			/* for reply */
	Bootp	*bp;
	Udphdr	*up;
	Ipifc	*ifc;
	uchar	*e;			/* end of received message */
	uchar	*p;			/* options pointer */
	uchar	*max;			/* max end of reply */

	/* expanded to v6 */
	uchar	ciaddr[IPaddrlen];
	uchar	giaddr[IPaddrlen];

	/* parsed options */
	int	p9request;		/* flag: this is a bootp with plan9 options */
	int	genrequest;		/* flag: this is a bootp with generic options */
	int	dhcptype;		/* dhcp message type */
	int	leasetime;		/* dhcp lease */
	uchar	ip[IPaddrlen];		/* requested address */
	uchar	server[IPaddrlen];	/* server address */
	char	msg[ERRMAX];		/* error message */
	char	vci[32];		/* vendor class id */
	char	*id;			/* client id */
	uchar	requested[32];		/* requested params */
	uchar	vendorclass[32];
	char	cputype[32-3];

	Info	gii;			/* about target network */
	Info	ii;			/* about target system */
	int	staticbinding;

	uchar buf[2*1024];		/* message buffer */
};

#define TFTP "/lib/tftpd"

char	*blog = "ipboot";
char	*mysysname;
Ipifc	*ipifcs;
int	debug;
int	nobootp;
long	now;
int	slowstat, slowdyn;
char	net[256];

int	pptponly;	/* only answer request that came from the pptp server */
int	mute, mutestat;
int	minlease = MinLease;
int	staticlease = StaticLease;

uvlong	start;

static int v6opts;

/* option magic */
char plan9opt[4] = { 'p', '9', ' ', ' ' };
char genericopt[4] = { 0x63, 0x82, 0x53, 0x63 };

/* well known addresses */
uchar zeros[Maxhwlen];

/* option debug buffer */
char optbuf[1024];
char *op;
char *oe = optbuf + sizeof(optbuf);

char *optname[256] =
{
[OBend]			"end",
[OBpad]			"pad",
[OBmask]		"mask",
[OBtimeoff]		"timeoff",
[OBrouter]		"router",
[OBtimeserver]		"time",
[OBnameserver]		"name",
[OBdnserver]		"dns",
[OBlogserver]		"log",
[OBcookieserver]	"cookie",
[OBlprserver]		"lpr",
[OBimpressserver]	"impress",
[OBrlserver]		"rl",
[OBhostname]		"host",
[OBbflen]		"bflen",
[OBdumpfile]		"dumpfile",
[OBdomainname]		"dom",
[OBswapserver]		"swap",
[OBrootpath]		"rootpath",
[OBextpath]		"extpath",
[OBipforward]		"ipforward",
[OBnonlocal]		"nonlocal",
[OBpolicyfilter]	"policyfilter",
[OBmaxdatagram]		"maxdatagram",
[OBttl]			"ttl",
[OBpathtimeout]		"pathtimeout",
[OBpathplateau]		"pathplateau",
[OBmtu]			"mtu",
[OBsubnetslocal]	"subnetslocal",
[OBbaddr]		"baddr",
[OBdiscovermask]	"discovermask",
[OBsupplymask]		"supplymask",
[OBdiscoverrouter]	"discoverrouter",
[OBrsserver]		"rsserver",
[OBstaticroutes]	"staticroutes",
[OBtrailerencap]	"trailerencap",
[OBarptimeout]		"arptimeout",
[OBetherencap]		"etherencap",
[OBtcpttl]		"tcpttl",
[OBtcpka]		"tcpka",
[OBtcpkag]		"tcpkag",
[OBnisdomain]		"nisdomain",
[OBniserver]		"niserver",
[OBntpserver]		"ntpserver",
[OBvendorinfo]		"vendorinfo",
[OBnetbiosns]		"NBns",
[OBnetbiosdds]		"NBdds",
[OBnetbiostype]		"NBtype",
[OBnetbiosscope]	"NBscope",
[OBxfontserver]		"xfont",
[OBxdispmanager]	"xdisp",
[OBnisplusdomain]	"NPdomain",
[OBnisplusserver]	"NP",
[OBhomeagent]		"homeagent",
[OBsmtpserver]		"smtp",
[OBpop3server]		"pop3",
[OBnntpserver]		"nntp",
[OBwwwserver]		"www",
[OBfingerserver]	"finger",
[OBircserver]		"ircserver",
[OBstserver]		"stserver",
[OBstdaserver]		"stdaserver",

/* dhcp options */
[ODipaddr]		"ip",
[ODlease]		"leas",
[ODoverload]		"overload",
[ODtype]		"typ",
[ODserverid]		"sid",
[ODparams]		"params",
[ODmessage]		"message",
[ODmaxmsg]		"maxmsg",
[ODrenewaltime]		"renewaltime",
[ODrebindingtime]	"rebindingtime",
[ODvendorclass]		"vendorclass",
[ODclientid]		"cid",
[ODtftpserver]		"tftpserver",
[ODbootfile]		"bf",
};

void	addropt(Req*, int, uchar*);
void	addrsopt(Req*, int, uchar**, int);
void	arpenter(uchar*, uchar*, uchar*);
void	bootp(Req*);
void	byteopt(Req*, int, uchar);
void	dhcp(Req*);
void	hexopt(Req*, int, char*);
void	logdhcp(Req*);
void	logdhcpout(Req *, char *);
void	longopt(Req*, int, long);
void	maskopt(Req*, int, uchar*);
void	miscoptions(Req*, uchar*);
int	openlisten(char *net);
void	p9addrsopt(Req *rp, int t, uchar **ip, int i);
void	parseoptions(Req*);
void	proto(Req*, int);
void	rcvdecline(Req*);
void	rcvdiscover(Req*);
void	rcvinform(Req*);
void	rcvrelease(Req*);
void	rcvrequest(Req*);
int	readlast(int, uchar*, int);
char*	readsysname(void);
void	remrequested(Req*, int);
void	sendack(Req*, uchar*, int, int);
void	sendnak(Req*, uchar*, char*);
void	sendoffer(Req*, uchar*, int);
void	stringopt(Req*, int, char*);
void	termopt(Req*);
int	validip(uchar*);
void	vectoropt(Req*, int, uchar*, int);

void
timestamp(char *tag)
{
	uvlong t;

	t = nsec()/1000;
	syslog(0, blog, "%s %lludµs", tag, t - start);
}

void
usage(void)
{
	fprint(2, "usage: dhcp [-dmnprsSZ] [-f directory] [-M minlease] "
		"[-x netmtpt] [-Z staticlease] addr n [addr n] ...\n");
	exits("usage");
}

void
main(int argc, char **argv)
{
	int i, n, fd;
	uchar ip[IPaddrlen];
	Req r;

	setnetmtpt(net, sizeof net, nil);

	fmtinstall('E', eipfmt);
	fmtinstall('I', eipfmt);
	fmtinstall('V', eipfmt);
	fmtinstall('M', eipfmt);
	fmtinstall('H', encodefmt);

	ARGBEGIN {
	case '6':
		v6opts = 1;
		break;
	case 'd':
		debug = 1;
		break;
	case 'f':
		ndbfile = EARGF(usage());
		break;
	case 'm':
		mute = 1;
		break;
	case 'M':
		minlease = atoi(EARGF(usage()));
		if(minlease <= 0)
			minlease = MinLease;
		break;
	case 'n':
		nobootp = 1;
		break;
	case 'p':
		pptponly = 1;
		break;
	case 'r':
		mutestat = 1;
		break;
	case 's':
		slowstat = 1;
		break;
	case 'S':
		slowdyn = 1;
		break;
	case 'x':
		setnetmtpt(net, sizeof net, EARGF(usage()));
		break;
	case 'Z':
		staticlease = atoi(EARGF(usage()));
		if(staticlease <= 0)
			staticlease = StaticLease;
		break;
	default:
		usage();
		break;
	} ARGEND;

	while(argc > 1){
		if(parseip(ip, argv[0]) == -1 || !validip(ip))
			usage();
		n = atoi(argv[1]);
		if(n <= 0)
			usage();
		initbinding(ip, n);
		argc -= 2;
		argv += 2;
	}

	/* for debugging */
	for(i = 0; i < 256; i++)
		if(optname[i] == 0)
			optname[i] = smprint("%d", i);

	/* what is my name? */
	mysysname = readsysname();

	/* put process in background */
	if(!debug)
	switch(rfork(RFNOTEG|RFPROC|RFFDG)) {
	case -1:
		fatal("fork: %r");
	case 0:
		break;
	default:
		exits(0);
	}

	if (chdir(TFTP) < 0)
		warning("can't change directory to %s: %r", TFTP);
	fd = openlisten(net);

	for(;;){
		memset(&r, 0, sizeof(r));
		r.fd = fd;
		n = readlast(r.fd, r.buf, sizeof(r.buf));
		if(n < Udphdrsize)
			fatal("error reading requests: %r");
		start = nsec()/1000;
		op = optbuf;
		*op = 0;
		proto(&r, n);
	}
}

void
proto(Req *rp, int n)
{
	now = time(0);

	rp->e = rp->buf + n;
	rp->bp = (Bootp*)rp->buf;
	rp->up = (Udphdr*)rp->buf;
	rp->max = rp->buf + Udphdrsize + MINSUPPORTED - IPUDPHDRSIZE;
	rp->p = rp->bp->optdata;
	v4tov6(rp->giaddr, rp->bp->giaddr);
	v4tov6(rp->ciaddr, rp->bp->ciaddr);

	if(pptponly && rp->bp->htype != 0)
		return;

	if(rp->bp->op != Bootrequest){
		warning("not bootrequest");
		return;
	}

	if(!isv4(rp->up->laddr))
		return;

	ipifcs = readipifc(net, ipifcs, -1);
	if((rp->ifc = findifc(rp->up->ifcaddr)) == nil){
		warning("no interface");
		return;
	}
	if(validip(rp->giaddr)){
		/* info about gateway */
		if(lookupip(rp->giaddr, nil, nil, &rp->gii, 1) < 0){
			warning("unknown gateway %I", rp->giaddr);
			return;
		}
		rp->gii.ifc = nil;
	} else {
		/* no gateway, directly connected */
		if(ipcmp(rp->up->laddr, IPv4bcast) != 0 && localonifc(rp->up->laddr, rp->ifc) == nil){
			warning("wrong network %I->%I on %s",
				rp->up->raddr, rp->up->laddr, rp->ifc->dev);
			return;
		}
		memset(&rp->gii, 0, sizeof(rp->gii));
		rp->gii.ifc = rp->ifc;
	}

	if(rp->e < (uchar*)rp->bp->sname){
		warning("packet too short");
		return;
	}
	if(rp->e >= rp->bp->optdata){
		if(memcmp(rp->bp->optmagic, plan9opt, sizeof(rp->bp->optmagic)) == 0)
			rp->p9request = 1;
		if(memcmp(rp->bp->optmagic, genericopt, sizeof(rp->bp->optmagic)) == 0) {
			rp->genrequest = 1;
			parseoptions(rp);
		}
	}
	rp->p = rp->bp->optdata;

	/*  If no id is specified, make one from the hardware address
	 *  of the target.  We assume all zeros is not a hardware address
	 *  which could be a mistake.
	 */
	if(rp->id == nil){
		static char hwaid[Maxstr];

		if(rp->bp->hlen > Maxhwlen || memcmp(zeros, rp->bp->chaddr, rp->bp->hlen) == 0){
			warning("no chaddr");
			return;
		}
		snprint(hwaid, sizeof(hwaid), "hwa%2.2ux_%.*lH", rp->bp->htype, rp->bp->hlen, rp->bp->chaddr);
		rp->id = hwaid;
	}

	/* info about target system */
	if(lookup(rp->bp, &rp->ii, &rp->gii) == 0)
		if(rp->ii.indb && rp->ii.dhcpgroup[0] == 0)
			rp->staticbinding = 1;

	if(rp->dhcptype)
		dhcp(rp);
	else
		bootp(rp);
	timestamp("done");
}

static void
slowdelay(Req *rp)
{
	if(slowstat && rp->staticbinding || slowdyn && !rp->staticbinding)
		sleep(2000);
}

void
dhcp(Req *rp)
{
	logdhcp(rp);

	switch(rp->dhcptype){
	case Discover:
		slowdelay(rp);
		rcvdiscover(rp);
		break;
	case Request:
		rcvrequest(rp);
		break;
	case Decline:
		rcvdecline(rp);
		break;
	case Release:
		rcvrelease(rp);
		break;
	case Inform:
		rcvinform(rp);
		break;
	}
}

void
rcvdiscover(Req *rp)
{
	Binding *b, *nb;

	if(rp->staticbinding){
		sendoffer(rp, rp->ii.ipaddr, (staticlease > minlease? staticlease: minlease));
		return;
	}

	/*
	 *  first look for an outstanding offer
	 */
	b = idtooffer(rp->id, &rp->gii);

	/*
	 * rfc2131 says:
	 *   If an address is available, the new address
	 *   SHOULD be chosen as follows:
	 *
	 *      o The client's current address as recorded in the client's current
	 *        binding, ELSE
	 *
	 *      o The client's previous address as recorded in the client's (now
	 *        expired or released) binding, if that address is in the server's
	 *        pool of available addresses and not already allocated, ELSE
	 *
	 *      o The address requested in the 'Requested IP Address' option, if that
	 *        address is valid and not already allocated, ELSE
	 *
	 *      o A new address allocated from the server's pool of available
	 *        addresses; the address is selected based on the subnet from which
	 *        the message was received (if 'giaddr' is 0) or on the address of
	 *        the relay agent that forwarded the message ('giaddr' when not 0).
	 */
	if(b == nil){
		b = idtobinding(rp->id, &rp->gii, 1);
		if(b && b->boundto && strcmp(b->boundto, rp->id) != 0)
		if(validip(rp->ip) && samenet(rp->ip, &rp->gii)){
			nb = iptobinding(rp->ip, 0);
			if(nb && nb->lease < now)
				b = nb;
		}
	}
	if(b == nil){
		warning("!Discover(%s via %I on %s): no binding %I",
			rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
		return;
	}
	mkoffer(b, rp->id, rp->leasetime);
	sendoffer(rp, b->ip, b->offer);
}

void
rcvrequest(Req *rp)
{
	Binding *b;

	if(validip(rp->server)){
		/* this is a reply to an offer - SELECTING */

		/* check for hard assignment */
		if(rp->staticbinding){
			if(findifc(rp->server) != rp->ifc) {
				warning("!Request(%s via %I on %s): for server %I not me",
					rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->server);
			} else
				sendack(rp, rp->ii.ipaddr,
					(staticlease > minlease? staticlease:
					minlease), 1);
			return;
		}

		b = idtooffer(rp->id, &rp->gii);

		/* if we don't have an offer, nak */
		if(b == nil){
			warning("!Request(%s via %I on %s): no offer",
				rp->id, rp->gii.ipaddr, rp->ifc->dev);
			if(findifc(rp->server) == rp->ifc)
				sendnak(rp, rp->server, "no offer for you");
			return;
		}

		/* if not for me, retract offer */
		if(findifc(rp->server) != rp->ifc){
			b->expoffer = 0;
			warning("!Request(%s via %I on %s): for server %I not me",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->server);
			return;
		}

		/*
		 *  if the client is confused about what we offered, nak.
		 *  client really shouldn't be specifying this when selecting
		 */
		if(validip(rp->ip) && ipcmp(rp->ip, b->ip) != 0){
			warning("!Request(%s via %I on %s): requests %I, not %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip, b->ip);
			sendnak(rp, rp->ip, "bad ip address option");
			return;
		}
		if(commitbinding(b) < 0){
			warning("!Request(%s via %I on %s): can't commit %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, b->ip);
			sendnak(rp, b->ip, "can't commit binding");
			return;
		}
		sendack(rp, b->ip, b->offer, 1);
	} else if(validip(rp->ip)){
		/*
		 *  checking address/net - INIT-REBOOT
		 *
		 *  This is a rebooting client that remembers its old
		 *  address.
		 */
		/* check for hard assignment */
		if(rp->staticbinding){
			if(ipcmp(rp->ip, rp->ii.ipaddr) != 0){
				warning("!Request(%s via %I on %s): %I not valid for %E",
					rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip, rp->bp->chaddr);
				sendnak(rp, rp->ip, "not valid");
			} else
				sendack(rp, rp->ip, (staticlease > minlease?
					staticlease: minlease), 1);
			return;
		}

		/* make sure the network makes sense */
		if(!samenet(rp->ip, &rp->gii)){
			warning("!Request(%s via %I on %s): bad forward of %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
			return;
		}
		b = iptobinding(rp->ip, 0);
		if(b == nil){
			warning("!Request(%s via %I on %s): no binding for %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
			return;
		}
		if(ipcmp(rp->ip, b->ip) != 0 || now > b->lease){
			warning("!Request(%s via %I on %s): %I not valid",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
			sendnak(rp, rp->ip, "not valid");
			return;
		}
		b->offer = b->lease - now;
		sendack(rp, b->ip, b->offer, 1);
	} else if(validip(rp->ciaddr)){
		/*
		 *  checking address - RENEWING or REBINDING
		 *
		 *  these states are indistinguishable in our action.  The only
		 *  difference is how close to lease expiration the client is.
		 *  If it is really close, it broadcasts the request hoping that
		 *  some server will answer.
		 */

		/* check for hard assignment */
		if(rp->staticbinding){
			if(ipcmp(rp->ciaddr, rp->ii.ipaddr) != 0){
				warning("!Request(%s via %I on %s): %I not valid",
					rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ciaddr);
				sendnak(rp, rp->ciaddr, "not valid");
			} else
				sendack(rp, rp->ciaddr, (staticlease > minlease?
					staticlease: minlease), 1);
			return;
		}

		/* make sure the network makes sense */
		if(!samenet(rp->ciaddr, &rp->gii)){
			warning("!Request(%s via %I on %s): bad forward of %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ciaddr);
			return;
		}
		b = iptobinding(rp->ciaddr, 0);
		if(b == nil){
			warning("!Request(%s via %I on %s): no binding for %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ciaddr);
			return;
		}
		if(ipcmp(rp->ciaddr, b->ip) != 0){
			warning("!Request(%s via %I on %s): %I not valid",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ciaddr);
			sendnak(rp, rp->ciaddr, "invalid ip address");
			return;
		}
		mkoffer(b, rp->id, rp->leasetime);
		if(commitbinding(b) < 0){
			warning("!Request(%s via %I on %s): can't commit %I",
				rp->id, rp->gii.ipaddr, rp->ifc->dev, b->ip);
			sendnak(rp, b->ip, "can't commit binding");
			return;
		}
		sendack(rp, b->ip, b->offer, 1);
	}
}

void
rcvdecline(Req *rp)
{
	Binding *b;
	char buf[64];

	if(rp->staticbinding)
		return;

	b = idtooffer(rp->id, &rp->gii);
	if(b == nil){
		warning("!Decline(%s via %I on %s): no binding",
			rp->id, rp->gii.ipaddr, rp->ifc->dev);
		return;
	}

	/* mark ip address as in use */
	snprint(buf, sizeof(buf), "declined by %s", rp->id);
	mkoffer(b, buf, 0x7fffffff);
	commitbinding(b);
}

void
rcvrelease(Req *rp)
{
	Binding *b;

	if(rp->staticbinding)
		return;

	b = idtobinding(rp->id, &rp->gii, 0);
	if(b == nil){
		warning("!Release(%s via %I on %s): no binding",
			rp->id, rp->gii.ipaddr, rp->ifc->dev);
		return;
	}
	if(strcmp(rp->id, b->boundto) != 0){
		warning("!Release(%s via %I on %s): invalid release of %I",
			rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
		return;
	}
	warning("Release(%s via %I on %s): releasing %I",
		b->boundto, rp->gii.ipaddr, rp->ifc->dev, b->ip);
	if(releasebinding(b, rp->id) < 0)
		warning("release: couldn't release");
}

void
rcvinform(Req *rp)
{
	Binding *b;

	if(rp->staticbinding){
		sendack(rp, rp->ii.ipaddr, 0, 0);
		return;
	}

	b = iptobinding(rp->ciaddr, 0);
	if(b == nil){
		warning("!Inform(%s via %I on %s): no binding for %I",
			rp->id, rp->gii.ipaddr, rp->ifc->dev, rp->ip);
		return;
	}
	sendack(rp, b->ip, 0, 0);
}

int
setsiaddr(uchar *siaddr, uchar *saddr, uchar *laddr)
{
	if(ipcmp(saddr, IPnoaddr) != 0){
		v6tov4(siaddr, saddr);
		return 0;
	} else {
		v6tov4(siaddr, laddr);
		return 1;
	}
}

int
ismuted(Req *rp)
{
	return mute || (mutestat && rp->staticbinding);
}

void
sendoffer(Req *rp, uchar *ip, int offer)
{
	int n;
	ushort flags;
	Bootp *bp;
	Udphdr *up;

	bp = rp->bp;
	up = rp->up;

	localip(up->laddr, ip, rp->ifc);

	flags = nhgets(bp->flags);
	if(validip(rp->giaddr)){
		ipmove(up->raddr, rp->giaddr);
		hnputs(up->rport, 67);
	} else if(flags & Fbroadcast){
		ipmove(up->raddr, IPv4bcast);
		hnputs(up->rport, 68);
	} else {
		ipmove(up->raddr, ip);
		if(bp->htype == 1)
			arpenter(up->raddr, bp->chaddr, up->laddr);
		hnputs(up->rport, 68);
	}

	/*
	 *  fill in standard bootp part
	 */
	bp->op = Bootreply;
	bp->hops = 0;
	hnputs(bp->secs, 0);
	memset(bp->ciaddr, 0, sizeof(bp->ciaddr));
	v6tov4(bp->giaddr, rp->giaddr);
	v6tov4(bp->yiaddr, ip);
	setsiaddr(bp->siaddr, rp->ii.tftp, up->laddr);
	strncpy(bp->sname, mysysname, sizeof(bp->sname));
	strncpy(bp->file, rp->ii.bootf, sizeof(bp->file));

	/*
	 *  set options
	 */
	byteopt(rp, ODtype, Offer);
	longopt(rp, ODlease, offer);
	addropt(rp, ODserverid, up->laddr);
	miscoptions(rp, ip);
	termopt(rp);

	logdhcpout(rp, "Offer");

	/*
	 *  send
	 */
	n = rp->p - rp->buf;
	if(!ismuted(rp) && write(rp->fd, rp->buf, n) != n)
		warning("offer: write failed: %r");
}

void
sendack(Req *rp, uchar *ip, int offer, int sendlease)
{
	int n;
	ushort flags;
	Bootp *bp;
	Udphdr *up;

	bp = rp->bp;
	up = rp->up;

	localip(up->laddr, ip, rp->ifc);

	flags = nhgets(bp->flags);
	if(validip(rp->giaddr)){
		ipmove(up->raddr, rp->giaddr);
		hnputs(up->rport, 67);
	} else if(flags & Fbroadcast){
		ipmove(up->raddr, IPv4bcast);
		hnputs(up->rport, 68);
	} else {
		ipmove(up->raddr, ip);
		if(bp->htype == 1)
			arpenter(up->raddr, bp->chaddr, up->laddr);
		hnputs(up->rport, 68);
	}

	/*
	 *  fill in standard bootp part
	 */
	bp->op = Bootreply;
	bp->hops = 0;
	hnputs(bp->secs, 0);
	v6tov4(bp->giaddr, rp->giaddr);
	v6tov4(bp->yiaddr, ip);
	setsiaddr(bp->siaddr, rp->ii.tftp, up->laddr);
	strncpy(bp->sname, mysysname, sizeof(bp->sname));
	strncpy(bp->file, rp->ii.bootf, sizeof(bp->file));

	/*
	 *  set options
	 */
	byteopt(rp, ODtype, Ack);
	if(sendlease){
		longopt(rp, ODlease, offer);
	}
	addropt(rp, ODserverid, up->laddr);
	miscoptions(rp, ip);
	termopt(rp);

	logdhcpout(rp, "Ack");

	/*
	 *  send
	 */
	n = rp->p - rp->buf;
	if(!ismuted(rp) && write(rp->fd, rp->buf, n) != n)
		warning("ack: write failed: %r");
}

void
sendnak(Req *rp, uchar *ip, char *msg)
{
	int n;
	Bootp *bp;
	Udphdr *up;

	bp = rp->bp;
	up = rp->up;

	localip(up->laddr, ip, rp->ifc);

	/*
	 *  set destination (always broadcast)
	 */
	if(validip(rp->giaddr)){
		ipmove(up->raddr, rp->giaddr);
		hnputs(up->rport, 67);
	} else {
		ipmove(up->raddr, IPv4bcast);
		hnputs(up->rport, 68);
	}

	/*
	 *  fill in standard bootp part
	 */
	bp->op = Bootreply;
	bp->hops = 0;
	hnputs(bp->secs, 0);
	v6tov4(bp->giaddr, rp->giaddr);
	memset(bp->ciaddr, 0, sizeof(bp->ciaddr));
	memset(bp->yiaddr, 0, sizeof(bp->yiaddr));
	memset(bp->siaddr, 0, sizeof(bp->siaddr));

	/*
	 *  set options
	 */
	byteopt(rp, ODtype, Nak);
	addropt(rp, ODserverid, up->laddr);
	if(msg)
		stringopt(rp, ODmessage, msg);
	if(strncmp(rp->id, "id", 2) == 0)
		hexopt(rp, ODclientid, rp->id+2);
	termopt(rp);

	logdhcpout(rp, "Nak");

	/*
	 *  send nak
	 */
	n = rp->p - rp->buf;
	if(!ismuted(rp) && write(rp->fd, rp->buf, n) != n)
		warning("nak: write failed: %r");
}

void
bootp(Req *rp)
{
	int n;
	Bootp *bp;
	Udphdr *up;
	ushort flags;
	Info *iip;

	warning("bootp %s %I->%I from %s via %I on %s, file %s",
		rp->genrequest? "generic": (rp->p9request? "p9": ""),
		rp->up->raddr, rp->up->laddr,
		rp->id, rp->gii.ipaddr, rp->ifc->dev,
		rp->bp->file);

	if(nobootp)
		return;

	bp = rp->bp;
	up = rp->up;
	iip = &rp->ii;

	if(rp->staticbinding == 0){
		warning("bootp from unknown %s via %I on %s",
			rp->id, rp->gii.ipaddr, rp->ifc->dev);
		return;
	}

	/* ignore if not for us */
	if(*bp->sname){
		if(strcmp(bp->sname, mysysname) != 0){
			bp->sname[20] = 0;
			warning("bootp for server %s", bp->sname);
			return;
		}
	} else
		slowdelay(rp);

	/* ignore file for sgi arcs command bootp(); */
	if(strcmp(bp->file, ";") == 0)
		*bp->file = 0;

	/* ignore if we don't know what file to load */
	if(*bp->file == 0){
		if(rp->genrequest && *iip->bootf2) /* if not plan 9 & have alternate file... */
			strncpy(bp->file, iip->bootf2, sizeof(bp->file));
		else if(*iip->bootf)
			strncpy(bp->file, iip->bootf, sizeof(bp->file));
		else if(*bp->sname) /* if we were asked, respond no matter what */
			bp->file[0] = '\0';
		else {
			warning("no bootfile for %I", iip->ipaddr);
			return;
		}
	}

	/* ignore if the file is unreadable */
	if((!rp->genrequest) && bp->file[0] && access(bp->file, 4) < 0){
		warning("inaccessible bootfile1 %s", bp->file);
		return;
	}

	bp->op = Bootreply;
	v6tov4(bp->yiaddr, iip->ipaddr);
	if(rp->p9request){
		warning("p9bootp: %I", iip->ipaddr);
		memmove(bp->optmagic, plan9opt, 4);
		rp->p += sprint((char*)rp->p, "%V %I %I %I",
			iip->ipmask+IPv4off, iip->fsip, iip->auip, iip->gwip);
		sprint(optbuf, "%s", (char*)(bp->optmagic));
	} else if(rp->genrequest){
		warning("genericbootp: %I", iip->ipaddr);
		memmove(bp->optmagic, genericopt, 4);
		miscoptions(rp, iip->ipaddr);
		termopt(rp);
	} else if(iip->vendor[0] != 0) {
		warning("bootp vendor field: %s", iip->vendor);
		memset(rp->p, 0, 128-4);
		rp->p += sprint((char*)bp->optmagic, "%s", iip->vendor);
	} else {
		memset(rp->p, 0, 128-4);
		rp->p += 128-4;
	}

	localip(up->laddr, iip->ipaddr, iip->ifc);

	flags = nhgets(bp->flags);
	if(validip(rp->giaddr)){
		ipmove(up->raddr, rp->giaddr);
		hnputs(up->rport, 67);
	} else if(flags & Fbroadcast){
		ipmove(up->raddr, IPv4bcast);
		hnputs(up->rport, 68);
	} else {
		v4tov6(up->raddr, bp->yiaddr);
		if(bp->htype == 1)
			arpenter(up->raddr, bp->chaddr, up->laddr);
		hnputs(up->rport, 68);
	}

	/*
	 *  our identity
	 */
	strncpy(bp->sname, mysysname, sizeof(bp->sname));

	/*
	 *  set tftp server
	 */
	setsiaddr(bp->siaddr, iip->tftp, up->laddr);
	if(rp->genrequest && *iip->bootf2)
		setsiaddr(bp->siaddr, iip->tftp2, up->laddr);

	/*
	 * RFC 1048 says that we must pad vendor field with
	 * zeros until we have a 64 byte field.
	 */
	n = rp->p - rp->bp->optdata;
	if(n < 64-4) {
		memset(rp->p, 0, (64-4)-n);
		rp->p += (64-4)-n;
	}

	/*
	 *  send
	 */
	n = rp->p - rp->buf;
	if(!ismuted(rp) && write(rp->fd, rp->buf, n) != n)
		warning("bootp: write failed: %r");

	warning("bootp via %I: file %s xid(%ux)flag(%ux)ci(%V)gi(%V)yi(%V)si(%V) %s",
			up->raddr, bp->file, nhgetl(bp->xid), nhgets(bp->flags),
			bp->ciaddr, bp->giaddr, bp->yiaddr, bp->siaddr,
			optbuf);
}

void
parseoptions(Req *rp)
{
	int n, c, code;
	uchar *o, *p;

	p = rp->p;

	while(p < rp->e){
		code = *p++;
		if(code == 255)
			break;
		if(code == 0)
			continue;

		/* ignore anything that's too long */
		n = *p++;
		o = p;
		p += n;
		if(p > rp->e)
			return;

		switch(code){
		case ODipaddr:	/* requested ip address */
			if(n == IPv4addrlen)
				v4tov6(rp->ip, o);
			break;
		case ODlease:	/* requested lease time */
			rp->leasetime = nhgetl(o);
			if(rp->leasetime > MaxLease || rp->leasetime < 0)
				rp->leasetime = MaxLease;
			break;
		case ODtype:
			c = *o;
			if(c < 10 && c > 0)
				rp->dhcptype = c;
			break;
		case ODserverid:
			if(n == IPv4addrlen)
				v4tov6(rp->server, o);
			break;
		case ODmessage:
			if(n > sizeof rp->msg-1)
				n = sizeof rp->msg-1;
			memmove(rp->msg, o, n);
			rp->msg[n] = 0;
			break;
		case ODmaxmsg:
			c = nhgets(o);
			c -= 28;
			c += Udphdrsize;
			if(c > 0)
				rp->max = rp->buf + c;
			break;
		case ODclientid:
			if(n <= 1)
				break;
			rp->id = toid(o, n);
			break;
		case ODparams:
			if(n > sizeof(rp->requested))
				n = sizeof(rp->requested);
			memmove(rp->requested, o, n);
			break;
		case ODvendorclass:
			if(n >= sizeof(rp->vendorclass))
				n = sizeof(rp->vendorclass)-1;
			memmove(rp->vendorclass, o, n);
			rp->vendorclass[n] = 0;
			if(strncmp((char*)rp->vendorclass, "p9-", 3) == 0)
				strncpy(rp->cputype, (char*)rp->vendorclass+3, sizeof(rp->cputype));
			break;
		case OBend:
			return;
		}
	}
}

void
remrequested(Req *rp, int opt)
{
	uchar *p;

	p = memchr(rp->requested, opt, sizeof(rp->requested));
	if(p != nil)
		*p = OBpad;
}

void
miscoptions(Req *rp, uchar *ip)
{
	int i, j, na;
	uchar *addrs[8];
	uchar *op, *omax;
	uchar x[nelem(addrs)*IPaddrlen], vopts[Maxoptlen];
	char *p;
	char *attr[100], **a;
	Ndbtuple *t;
	Iplifc *lifc;

	for(i=0; i<nelem(addrs); i++)
		addrs[i] = &x[i*IPaddrlen];

	/* always supply these */
	if(validip(rp->ii.ipmask))
		maskopt(rp, OBmask, rp->ii.ipmask);
	else if(validip(rp->gii.ipmask))
		maskopt(rp, OBmask, rp->gii.ipmask);
	else if((lifc = localonifc(ip, rp->ifc)) != nil)
		maskopt(rp, OBmask, lifc->mask);

	if(validip(rp->ii.gwip)){
		remrequested(rp, OBrouter);
		addropt(rp, OBrouter, rp->ii.gwip);
	} else if(validip(rp->gii.gwip)){
		remrequested(rp, OBrouter);
		addropt(rp, OBrouter, rp->gii.gwip);
	} else if(validip(rp->giaddr)){
		remrequested(rp, OBrouter);
		addropt(rp, OBrouter, rp->giaddr);
	}

	/*
	 * OBhostname for the HP4000M switches
	 * (this causes NT to log infinite errors - tough shit)
	 */
	if(*rp->ii.domain){
		remrequested(rp, OBhostname);
		stringopt(rp, OBhostname, rp->ii.domain);
	}
	if(*rp->ii.rootpath)
		stringopt(rp, OBrootpath, rp->ii.rootpath);

	/* figure out what we need to lookup */
	na = 0;
	a = attr;
	if(*rp->ii.domain == 0)
		a[na++] = "dom";
	for(i = 0; i < sizeof(rp->requested); i++)
		switch(rp->requested[i]){
		case OBrouter:
			a[na++] = "@ipgw";
			break;
		case OBdnserver:
			a[na++] = "@dns";
			break;
		case OBnetbiosns:
			a[na++] = "@wins";
			break;
		case OBsmtpserver:
			a[na++] = "@smtp";
			break;
		case OBpop3server:
			a[na++] = "@pop3";
			break;
		case OBwwwserver:
			a[na++] = "@www";
			break;
		case OBntpserver:
			a[na++] = "@ntp";
			break;
		case OBtimeserver:
			a[na++] = "@time";
			break;
		}
	if(strncmp((char*)rp->vendorclass, "plan9_", 6) == 0
	|| strncmp((char*)rp->vendorclass, "p9-", 3) == 0){
		a[na++] = "@fs";
		a[na++] = "@auth";
	}
	t = lookupinfo(ip, a, na);

	/* lookup anything we might be missing */
	if(*rp->ii.domain == 0)
		lookupname(rp->ii.domain, sizeof(rp->ii.domain), t);

	/* add any requested ones that we know about */
	for(i = 0; i < sizeof(rp->requested); i++)
		switch(rp->requested[i]){
		case OBrouter:
			j = lookupserver("ipgw", addrs, nelem(addrs), t);
			addrsopt(rp, OBrouter, addrs, j);
			break;
		case OBdnserver:
			j = lookupserver("dns", addrs, nelem(addrs), t);
			addrsopt(rp, OBdnserver, addrs, j);
			break;
		case OBhostname:
			if(*rp->ii.domain)
				stringopt(rp, OBhostname, rp->ii.domain);
			break;
		case OBdomainname:
			p = strchr(rp->ii.domain, '.');
			if(p != nil)
				stringopt(rp, OBdomainname, p+1);
			break;
		case OBnetbiosns:
			j = lookupserver("wins", addrs, nelem(addrs), t);
			addrsopt(rp, OBnetbiosns, addrs, j);
			break;
		case OBnetbiostype:
			/* p-node: peer to peer WINS queries */
			byteopt(rp, OBnetbiostype, 0x2);
			break;
		case OBsmtpserver:
			j = lookupserver("smtp", addrs, nelem(addrs), t);
			addrsopt(rp, OBsmtpserver, addrs, j);
			break;
		case OBpop3server:
			j = lookupserver("pop3", addrs, nelem(addrs), t);
			addrsopt(rp, OBpop3server, addrs, j);
			break;
		case OBwwwserver:
			j = lookupserver("www", addrs, nelem(addrs), t);
			addrsopt(rp, OBwwwserver, addrs, j);
			break;
		case OBntpserver:
			j = lookupserver("ntp", addrs, nelem(addrs), t);
			addrsopt(rp, OBntpserver, addrs, j);
			break;
		case OBtimeserver:
			j = lookupserver("time", addrs, nelem(addrs), t);
			addrsopt(rp, OBtimeserver, addrs, j);
			break;
		case OBttl:
			byteopt(rp, OBttl, 255);
			break;
		}

	/* add plan9 specific options */
	if(strncmp((char*)rp->vendorclass, "plan9_", 6) == 0
	|| strncmp((char*)rp->vendorclass, "p9-", 3) == 0){
		/* point to temporary area */
		op = rp->p;
		omax = rp->max;
		/* stash encoded options in vopts */
		rp->p = vopts;
		rp->max = vopts + sizeof(vopts) - 1;

		/* emit old v4 addresses first to make sure that they fit */
		addrsopt(rp, OP9fsv4, addrs, lookupserver("fs", addrs, nelem(addrs), t));
		addrsopt(rp, OP9authv4, addrs, lookupserver("auth", addrs, nelem(addrs), t));

		p9addrsopt(rp, OP9fs, addrs, lookupserver("fs", addrs, nelem(addrs), t));
		p9addrsopt(rp, OP9auth, addrs, lookupserver("auth", addrs, nelem(addrs), t));
		p9addrsopt(rp, OP9ipaddr, addrs, lookupserver("ip", addrs, nelem(addrs), t));
		p9addrsopt(rp, OP9ipmask, addrs, lookupserver("ipmask", addrs, nelem(addrs), t));
		p9addrsopt(rp, OP9ipgw, addrs, lookupserver("ipgw", addrs, nelem(addrs), t));

		/* point back to packet, encapsulate vopts into packet */
		j = rp->p - vopts;
		rp->p = op;
		rp->max = omax;
		vectoropt(rp, OBvendorinfo, vopts, j);
	}

	ndbfree(t);
}

int
openlisten(char *net)
{
	int fd, cfd;
	char data[128], devdir[40];

	sprint(data, "%s/udp!*!bootp", net);
	cfd = announce(data, devdir);
	if(cfd < 0)
		fatal("can't announce: %r");
	if(fprint(cfd, "headers") < 0)
		fatal("can't set header mode: %r");

	sprint(data, "%s/data", devdir);
	fd = open(data, ORDWR);
	if(fd < 0)
		fatal("open udp data: %r");
	return fd;
}

void
fatal(char *fmt, ...)
{
	char buf[Maxloglen];
	va_list arg;

	va_start(arg, fmt);
	vseprint(buf, buf+sizeof(buf), fmt, arg);
	va_end(arg);
	syslog(1, blog, "%s", buf);
	exits(buf);
}

void
warning(char *fmt, ...)
{
	char buf[Maxloglen];
	va_list arg;

	va_start(arg, fmt);
	vseprint(buf, buf+sizeof(buf), fmt, arg);
	va_end(arg);
	syslog(0, blog, "%s", buf);
	if(debug)
		fprint(2, "%s\n", buf);
}

char*
readsysname(void)
{
	static char name[128];
	char *p;
	int n, fd;

	fd = open("/dev/sysname", OREAD);
	if(fd >= 0){
		n = read(fd, name, sizeof(name)-1);
		close(fd);
		if(n > 0){
			name[n] = 0;
			return name;
		}
	}
	p = getenv("sysname");
	if(p == nil || *p == 0)
		return "unknown";
	return p;
}

extern int
validip(uchar *ip)
{
	if(ipcmp(ip, IPnoaddr) == 0)
		return 0;
	if(ipcmp(ip, v4prefix) == 0)
		return 0;
	return 1;
}

void
longopt(Req *rp, int t, long v)
{
	if(rp->p + 6 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = 4;
	hnputl(rp->p, v);
	rp->p += 4;

	op = seprint(op, oe, "%s(%ld)", optname[t], v);
}

void
addropt(Req *rp, int t, uchar *ip)
{
	if(rp->p + 6 > rp->max)
		return;
	if (!isv4(ip)) {
		if (debug)
			warning("not a v4 %s server: %I", optname[t], ip);
		return;
	}
	*rp->p++ = t;
	*rp->p++ = 4;
	memmove(rp->p, ip+IPv4off, 4);
	rp->p += 4;

	op = seprint(op, oe, "%s(%I)", optname[t], ip);
}

void
maskopt(Req *rp, int t, uchar *ip)
{
	if(rp->p + 6 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = 4;
	memmove(rp->p, ip+IPv4off, 4);
	rp->p += 4;

	op = seprint(op, oe, "%s(%M)", optname[t], ip);
}

void
addrsopt(Req *rp, int t, uchar **ip, int i)
{
	int v4s, n;

	if(i <= 0)
		return;
	if(rp->p + 2 + 4*i > rp->max)
		return;
	v4s = 0;
	for(n = i; n-- > 0; )
		if (isv4(ip[n]))
			v4s++;
	if (v4s <= 0) {
		if (debug)
			warning("no v4 %s servers", optname[t]);
		return;
	}
	*rp->p++ = t;
	*rp->p++ = 4*v4s;
	op = seprint(op, oe, " %s(", optname[t]);
	while(i-- > 0){
		if (!isv4(*ip)) {
			op = seprint(op, oe, " skipping %I ", *ip);
			continue;
		}
		v6tov4(rp->p, *ip);
		rp->p += 4;
		op = seprint(op, oe, "%I", *ip);
		ip++;
		if(i > 0)
			op = seprint(op, oe, " ");
	}
	op = seprint(op, oe, ")");
}

void
p9addrsopt(Req *rp, int t, uchar **ip, int i)
{
	char *pkt, *payload;

	if(i <= 0 || !v6opts)
		return;
	pkt = (char *)rp->p;
	*pkt++ = t;			/* option */
	pkt++;				/* fill in payload length below */
	payload = pkt;
	*pkt++ = i;			/* plan 9 address count */
	op = seprint(op, oe, " %s(", optname[t]);
	while(i-- > 0){
		pkt = seprint(pkt, (char *)rp->max, "%I", *ip);
		if ((uchar *)pkt+1 >= rp->max) {
			op = seprint(op, oe, "<out of mem1>)");
			return;
		}
		pkt++;			/* leave NUL as terminator */
		op = seprint(op, oe, "%I", *ip);
		ip++;
		if(i > 0)
			op = seprint(op, oe, " ");
	}
	if ((uchar *)pkt - rp->p > 0377) {
		op = seprint(op, oe, "<out of mem2>)");
		return;
	}
	op = seprint(op, oe, ")");
	rp->p[1] = pkt - payload;	/* payload length */
	rp->p = (uchar *)pkt;
}

void
byteopt(Req *rp, int t, uchar v)
{
	if(rp->p + 3 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = 1;
	*rp->p++ = v;

	op = seprint(op, oe, "%s(%d)", optname[t], v);
}

void
termopt(Req *rp)
{
	if(rp->p + 1 > rp->max)
		return;
	*rp->p++ = OBend;
}

void
stringopt(Req *rp, int t, char *str)
{
	int n;

	n = strlen(str);
	if(n > 255)
		n = 255;
	if(rp->p+n+2 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = n;
	memmove(rp->p, str, n);
	rp->p += n;

	op = seprint(op, oe, "%s(%s)", optname[t], str);
}

void
vectoropt(Req *rp, int t, uchar *v, int n)
{
	int i;

	if(n > 255) {
		n = 255;
		op = seprint(op, oe, "vectoropt len %d > 255 ", n);
	}
	if(rp->p+n+2 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = n;
	memmove(rp->p, v, n);
	rp->p += n;

	op = seprint(op, oe, "%s(", optname[t]);
	if(n > 0)
		op = seprint(op, oe, "%ud", v[0]);
	for(i = 1; i < n; i++)
		op = seprint(op, oe, " %ud", v[i]);
	op = seprint(op, oe, ")");
}

int
fromhex(int x)
{
	if(x >= '0' && x <= '9')
		return x - '0';
	return x - 'a';
}

void
hexopt(Req *rp, int t, char *str)
{
	int n;

	n = strlen(str);
	n /= 2;
	if(n > 255)
		n = 255;
	if(rp->p+n+2 > rp->max)
		return;
	*rp->p++ = t;
	*rp->p++ = n;
	while(n-- > 0){
		*rp->p++ = (fromhex(str[0])<<4)|fromhex(str[1]);
		str += 2;
	}

	op = seprint(op, oe, "%s(%s)", optname[t], str);
}

void
arpenter(uchar *ip, uchar *mac, uchar *src)
{
	char buf[256];
	int fd, n;

	snprint(buf, sizeof buf, "%s/arp", net);
	if((fd = open(buf, OWRITE)) < 0){
		warning("couldn't open %s: %r", buf);
		return;
	}
	n = snprint(buf, sizeof buf, "add ether %I %E %I\n", ip, mac, src);
	if(write(fd, buf, n) != n)
		warning("arpenter: %s: %r", buf);
	close(fd);
}

char *dhcpmsgname[] =
{
	[Discover]	"Discover",
	[Offer]		"Offer",
	[Request]	"Request",
	[Decline]	"Decline",
	[Ack]		"Ack",
	[Nak]		"Nak",
	[Release]	"Release",
	[Inform]	"Inform",
};

void
logdhcp(Req *rp)
{
	char buf[4096];
	char *p, *e;
	int i;

	p = buf;
	e = buf + sizeof(buf);
	if(rp->dhcptype > 0 && rp->dhcptype <= Inform)
		p = seprint(p, e, "%s(", dhcpmsgname[rp->dhcptype]);
	else
		p = seprint(p, e, "%d(", rp->dhcptype);
	p = seprint(p, e, "%I->%I) xid(%ux)flag(%ux)", rp->up->raddr, rp->up->laddr,
		nhgetl(rp->bp->xid), nhgets(rp->bp->flags));
	if(rp->bp->htype == 1)
		p = seprint(p, e, "ea(%E)", rp->bp->chaddr);
	if(validip(rp->ciaddr))
		p = seprint(p, e, "ci(%I)", rp->ciaddr);
	if(validip(rp->giaddr))
		p = seprint(p, e, "gi(%I)", rp->giaddr);
	if(validip(rp->ip))
		p = seprint(p, e, "ip(%I)", rp->ip);
	if(rp->id != nil)
		p = seprint(p, e, "id(%s)", rp->id);
	if(rp->leasetime)
		p = seprint(p, e, "leas(%d)", rp->leasetime);
	if(validip(rp->server))
		p = seprint(p, e, "sid(%I)", rp->server);
	p = seprint(p, e, "need(");
	for(i = 0; i < sizeof(rp->requested); i++)
		if(rp->requested[i] != 0)
			p = seprint(p, e, "%s ", optname[rp->requested[i]]);
	p = seprint(p, e, ")");

	USED(p);
	syslog(0, blog, "%s", buf);
}

void
logdhcpout(Req *rp, char *type)
{
	syslog(0, blog, "%s(%I->%I)id(%s)ci(%V)gi(%V)yi(%V)si(%V) %s",
		type, rp->up->laddr, rp->up->raddr, rp->id,
		rp->bp->ciaddr, rp->bp->giaddr, rp->bp->yiaddr, rp->bp->siaddr, optbuf);
}

/*
 *  if we get behind, it's useless to try answering since the sender
 *  will probably have retransmitted with a differnt sequence number.
 *  So dump all but the last message in the queue.
 */
void
ding(void*, char *msg)
{
	if(strstr(msg, "alarm"))
		noted(NCONT);
	else
		noted(NDFLT);
}

int
readlast(int fd, uchar *buf, int len)
{
	int lastn, n;

	notify(ding);

	lastn = 0;
	for(;;){
		alarm(20);
		n = read(fd, buf, len);
		alarm(0);
		if(n < 0){
			if(lastn > 0)
				return lastn;
			break;
		}
		lastn = n;
	}
	return read(fd, buf, len);
}