ethermedium.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

		if(!canrlock(ifc)){
			freeb(bp);
			continue;
		}
		if(waserror()){
			runlock(ifc);
			nexterror();
		}
		ifc->in++;
		bp->rp += ifc->m->hsize;
		if(ifc->lifc == nil)
			freeb(bp);
		else
			ipiput6(er->f, ifc, bp);
		runlock(ifc);
		poperror();
	}
}

static void
etheraddmulti(Ipifc *ifc, uchar *a, uchar *)
{
	uchar mac[6];
	char buf[64];
	Etherrock *er = ifc->arg;
	int version;

	version = multicastea(mac, a);
	sprint(buf, "addmulti %E", mac);
	switch(version){
	case V4:
		devtab[er->cchan4->type]->write(er->cchan4, buf, strlen(buf), 0);
		break;
	case V6:
		devtab[er->cchan6->type]->write(er->cchan6, buf, strlen(buf), 0);
		break;
	default:
		panic("etheraddmulti: version %d", version);
	}
}

static void
etherremmulti(Ipifc *ifc, uchar *a, uchar *)
{
	uchar mac[6];
	char buf[64];
	Etherrock *er = ifc->arg;
	int version;

	version = multicastea(mac, a);
	sprint(buf, "remmulti %E", mac);
	switch(version){
	case V4:
		devtab[er->cchan4->type]->write(er->cchan4, buf, strlen(buf), 0);
		break;
	case V6:
		devtab[er->cchan6->type]->write(er->cchan6, buf, strlen(buf), 0);
		break;
	default:
		panic("etherremmulti: version %d", version);
	}
}

/*
 *  send an ethernet arp
 *  (only v4, v6 uses the neighbor discovery, rfc1970)
 */
static void
sendarp(Ipifc *ifc, Arpent *a)
{
	int n;
	Block *bp;
	Etherarp *e;
	Etherrock *er = ifc->arg;

	/* don't do anything if it's been less than a second since the last */
	if(NOW - a->ctime < 1000){
		arprelease(er->f->arp, a);
		return;
	}

	/* remove all but the last message */
	while((bp = a->hold) != nil){
		if(bp == a->last)
			break;
		a->hold = bp->list;
		freeblist(bp);
	}

	/* try to keep it around for a second more */
	a->ctime = NOW;
	arprelease(er->f->arp, a);

	n = sizeof(Etherarp);
	if(n < a->type->mintu)
		n = a->type->mintu;
	bp = allocb(n);
	memset(bp->rp, 0, n);
	e = (Etherarp*)bp->rp;
	memmove(e->tpa, a->ip+IPv4off, sizeof(e->tpa));
	ipv4local(ifc, e->spa);
	memmove(e->sha, ifc->mac, sizeof(e->sha));
	memset(e->d, 0xff, sizeof(e->d));		/* ethernet broadcast */
	memmove(e->s, ifc->mac, sizeof(e->s));

	hnputs(e->type, ETARP);
	hnputs(e->hrd, 1);
	hnputs(e->pro, ETIP4);
	e->hln = sizeof(e->sha);
	e->pln = sizeof(e->spa);
	hnputs(e->op, ARPREQUEST);
	bp->wp += n;

	n = devtab[er->achan->type]->bwrite(er->achan, bp, 0);
	if(n < 0)
		print("arp: send: %r\n");
}

static void
resolveaddr6(Ipifc *ifc, Arpent *a)
{
	int sflag;
	Block *bp;
	Etherrock *er = ifc->arg;
	uchar ipsrc[IPaddrlen];

	/* don't do anything if it's been less than a second since the last */
	if(NOW - a->ctime < ReTransTimer){
		arprelease(er->f->arp, a);
		return;
	}

	/* remove all but the last message */
	while((bp = a->hold) != nil){
		if(bp == a->last)
			break;
		a->hold = bp->list;
		freeblist(bp);
	}

	/* try to keep it around for a second more */
	a->ctime = NOW;
	a->rtime = NOW + ReTransTimer;
	if(a->rxtsrem <= 0) {
		arprelease(er->f->arp, a);
		return;
	}

	a->rxtsrem--;
	arprelease(er->f->arp, a);

	if(sflag = ipv6anylocal(ifc, ipsrc)) 
		icmpns(er->f, ipsrc, sflag, a->ip, TARG_MULTI, ifc->mac);
}

/*
 *  send a gratuitous arp to refresh arp caches
 */
static void
sendgarp(Ipifc *ifc, uchar *ip)
{
	int n;
	Block *bp;
	Etherarp *e;
	Etherrock *er = ifc->arg;

	/* don't arp for our initial non address */
	if(ipcmp(ip, IPnoaddr) == 0)
		return;

	n = sizeof(Etherarp);
	if(n < ifc->m->mintu)
		n = ifc->m->mintu;
	bp = allocb(n);
	memset(bp->rp, 0, n);
	e = (Etherarp*)bp->rp;
	memmove(e->tpa, ip+IPv4off, sizeof(e->tpa));
	memmove(e->spa, ip+IPv4off, sizeof(e->spa));
	memmove(e->sha, ifc->mac, sizeof(e->sha));
	memset(e->d, 0xff, sizeof(e->d));		/* ethernet broadcast */
	memmove(e->s, ifc->mac, sizeof(e->s));

	hnputs(e->type, ETARP);
	hnputs(e->hrd, 1);
	hnputs(e->pro, ETIP4);
	e->hln = sizeof(e->sha);
	e->pln = sizeof(e->spa);
	hnputs(e->op, ARPREQUEST);
	bp->wp += n;

	n = devtab[er->achan->type]->bwrite(er->achan, bp, 0);
	if(n < 0)
		print("garp: send: %r\n");
}

static void
recvarp(Ipifc *ifc)
{
	int n;
	Block *ebp, *rbp;
	Etherarp *e, *r;
	uchar ip[IPaddrlen];
	static uchar eprinted[4];
	Etherrock *er = ifc->arg;

	ebp = devtab[er->achan->type]->bread(er->achan, ifc->maxtu, 0);
	if(ebp == nil) {
		print("arp: rcv: %r\n");
		return;
	}

	e = (Etherarp*)ebp->rp;
	switch(nhgets(e->op)) {
	default:
		break;

	case ARPREPLY:
		/* check for machine using my ip address */
		v4tov6(ip, e->spa);
		if(iplocalonifc(ifc, ip) || ipproxyifc(er->f, ifc, ip)){
			if(memcmp(e->sha, ifc->mac, sizeof(e->sha)) != 0){
				print("arprep: 0x%E/0x%E also has ip addr %V\n",
					e->s, e->sha, e->spa);
				break;
			}
		}

		/* make sure we're not entering broadcast addresses */
		if(ipcmp(ip, ipbroadcast) == 0 ||
			!memcmp(e->sha, etherbroadcast, sizeof(e->sha))){
			print("arprep: 0x%E/0x%E cannot register broadcast address %I\n",
				e->s, e->sha, e->spa);
			break;
		}

		arpenter(er->f, V4, e->spa, e->sha, sizeof(e->sha), 0);
		break;

	case ARPREQUEST:
		/* don't answer arps till we know who we are */
		if(ifc->lifc == 0)
			break;

		/* check for machine using my ip or ether address */
		v4tov6(ip, e->spa);
		if(iplocalonifc(ifc, ip) || ipproxyifc(er->f, ifc, ip)){
			if(memcmp(e->sha, ifc->mac, sizeof(e->sha)) != 0){
				if (memcmp(eprinted, e->spa, sizeof(e->spa))){
					/* print only once */
					print("arpreq: 0x%E also has ip addr %V\n", e->sha, e->spa);
					memmove(eprinted, e->spa, sizeof(e->spa));
				}
			}
		} else {
			if(memcmp(e->sha, ifc->mac, sizeof(e->sha)) == 0){
				print("arpreq: %V also has ether addr %E\n", e->spa, e->sha);
				break;
			}
		}

		/* refresh what we know about sender */
		arpenter(er->f, V4, e->spa, e->sha, sizeof(e->sha), 1);

		/* answer only requests for our address or systems we're proxying for */
		v4tov6(ip, e->tpa);
		if(!iplocalonifc(ifc, ip))
		if(!ipproxyifc(er->f, ifc, ip))
			break;

		n = sizeof(Etherarp);
		if(n < ifc->mintu)
			n = ifc->mintu;
		rbp = allocb(n);
		r = (Etherarp*)rbp->rp;
		memset(r, 0, sizeof(Etherarp));
		hnputs(r->type, ETARP);
		hnputs(r->hrd, 1);
		hnputs(r->pro, ETIP4);
		r->hln = sizeof(r->sha);
		r->pln = sizeof(r->spa);
		hnputs(r->op, ARPREPLY);
		memmove(r->tha, e->sha, sizeof(r->tha));
		memmove(r->tpa, e->spa, sizeof(r->tpa));
		memmove(r->sha, ifc->mac, sizeof(r->sha));
		memmove(r->spa, e->tpa, sizeof(r->spa));
		memmove(r->d, e->sha, sizeof(r->d));
		memmove(r->s, ifc->mac, sizeof(r->s));
		rbp->wp += n;

		n = devtab[er->achan->type]->bwrite(er->achan, rbp, 0);
		if(n < 0)
			print("arp: write: %r\n");
	}
	freeb(ebp);
}

static void
recvarpproc(void *v)
{
	Ipifc *ifc = v;
	Etherrock *er = ifc->arg;

	er->arpp = up;
	if(waserror()){
		er->arpp = 0;
		pexit("hangup", 1);
	}
	for(;;)
		recvarp(ifc);
}

static int
multicastea(uchar *ea, uchar *ip)
{
	int x;

	switch(x = ipismulticast(ip)){
	case V4:
		ea[0] = 0x01;
		ea[1] = 0x00;
		ea[2] = 0x5e;
		ea[3] = ip[13] & 0x7f;
		ea[4] = ip[14];
		ea[5] = ip[15];
		break;
 	case V6:
 		ea[0] = 0x33;
 		ea[1] = 0x33;
 		ea[2] = ip[12];
		ea[3] = ip[13];
 		ea[4] = ip[14];
 		ea[5] = ip[15];
 		break;
	}
	return x;
}

/*
 *  fill in an arp entry for broadcast or multicast
 *  addresses.  Return the first queued packet for the
 *  IP address.
 */
static Block*
multicastarp(Fs *f, Arpent *a, Medium *medium, uchar *mac)
{
	/* is it broadcast? */
	switch(ipforme(f, a->ip)){
	case Runi:
		return nil;
	case Rbcast:
		memset(mac, 0xff, 6);
		return arpresolve(f->arp, a, medium, mac);
	default:
		break;
	}

	/* if multicast, fill in mac */
	switch(multicastea(mac, a->ip)){
	case V4:
	case V6:
		return arpresolve(f->arp, a, medium, mac);
	}

	/* let arp take care of it */
	return nil;
}

void
ethermediumlink(void)
{
	addipmedium(&ethermedium);
	addipmedium(&gbemedium);
}


static void 
etherpref2addr(uchar *pref, uchar *ea)
{
	pref[8]  = ea[0] | 0x2;
	pref[9]  = ea[1];
	pref[10] = ea[2];
	pref[11] = 0xFF;
	pref[12] = 0xFE;
	pref[13] = ea[3];
	pref[14] = ea[4];
	pref[15] = ea[5];
}