dn.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

 */
RR*
rrlookup(DN *dp, int type, int flag)
{
	RR *rp, *first, **last;

	assert(dp->magic == DNmagic);

	first = 0;
	last = &first;
	lock(&dnlock);

	/* try for an authoritative db entry */
	for(rp = dp->rr; rp; rp = rp->next){
		assert(rp->magic == RRmagic && rp->cached);
		if(rp->db)
		if(rp->auth)
		if(tsame(type, rp->type))
			last = rrcopy(rp, last);
	}
	if(first)
		goto out;

	/* try for an living authoritative network entry */
	for(rp = dp->rr; rp; rp = rp->next){
		if(!rp->db)
		if(rp->auth)
		if(rp->ttl + 60 > now)
		if(tsame(type, rp->type)){
			if(flag == NOneg && rp->negative)
				goto out;
			last = rrcopy(rp, last);
		}
	}
	if(first)
		goto out;

	/* try for an living unauthoritative network entry */
	for(rp = dp->rr; rp; rp = rp->next){
		if(!rp->db)
		if(rp->ttl + 60 > now)
		if(tsame(type, rp->type)){
			if(flag == NOneg && rp->negative)
				goto out;
			last = rrcopy(rp, last);
		}
	}
	if(first)
		goto out;

	/* try for an unauthoritative db entry */
	for(rp = dp->rr; rp; rp = rp->next){
		if(rp->db)
		if(tsame(type, rp->type))
			last = rrcopy(rp, last);
	}
	if(first)
		goto out;

	/* otherwise, settle for anything we got (except for negative caches)  */
	for(rp = dp->rr; rp; rp = rp->next){
		if(tsame(type, rp->type)){
			if(rp->negative)
				goto out;
			last = rrcopy(rp, last);
		}
	}

out:
	unlock(&dnlock);
	unique(first);
	return first;
}

/*
 *  convert an ascii RR type name to its integer representation
 */
int
rrtype(char *atype)
{
	int i;

	for(i = 0; i <= Tall; i++)
		if(rrtname[i] && strcmp(rrtname[i], atype) == 0)
			return i;

	// make any a synonym for all
	if(strcmp(atype, "any") == 0)
		return Tall;
	return atoi(atype);
}

/*
 *  convert an integer RR type to it's ascii name
 */
char*
rrname(int type, char *buf, int len)
{
	char *t;

	t = 0;
	if(type <= Tall)
		t = rrtname[type];
	if(t==0){
		snprint(buf, len, "%d", type);
		t = buf;
	}
	return t;
}

/*
 *  return 0 if not a supported rr type
 */
int
rrsupported(int type)
{
	if(type < 0 || type >Tall)
		return 0;
	return rrtname[type] != 0;
}

/*
 *  compare 2 types
 */
int
tsame(int t1, int t2)
{
	return t1 == t2 || t1 == Tall;
}

/*
 *  Add resource records to a list, duplicate them if they are cached
 *  RR's since these are shared.
 */
RR*
rrcat(RR **start, RR *rp)
{
	RR **last;

	last = start;
	while(*last != 0)
		last = &(*last)->next;

	*last = rp;
	return *start;
}

/*
 *  remove negative cache rr's from an rr list
 */
RR*
rrremneg(RR **l)
{
	RR **nl, *rp;
	RR *first;

	first = nil;
	nl = &first;
	while(*l != nil){
		rp = *l;
		if(rp->negative){
			*l = rp->next;
			*nl = rp;
			nl = &rp->next;
			*nl = nil;
		} else
			l = &rp->next;
	}

	return first;
}

/*
 *  remove rr's of a particular type from an rr list
 */
RR*
rrremtype(RR **l, int type)
{
	RR **nl, *rp;
	RR *first;

	first = nil;
	nl = &first;
	while(*l != nil){
		rp = *l;
		if(rp->type == type){
			*l = rp->next;
			*nl = rp;
			nl = &rp->next;
			*nl = nil;
		} else
			l = &(*l)->next;
	}

	return first;
}

/*
 *  print conversion for rr records
 */
int
rrfmt(Fmt *f)
{
	RR *rp;
	char *strp;
	Fmt fstr;
	int rv;
	char buf[Domlen];
	Server *s;
	Txt *t;

	fmtstrinit(&fstr);

	rp = va_arg(f->args, RR*);
	if(rp == 0){
		fmtprint(&fstr, "<null>");
		goto out;
	}

	fmtprint(&fstr, "%s %s", rp->owner->name,
		rrname(rp->type, buf, sizeof buf));

	if(rp->negative){
		fmtprint(&fstr, "\tnegative - rcode %d", rp->negrcode);
		goto out;
	}

	switch(rp->type){
	case Thinfo:
		fmtprint(&fstr, "\t%s %s", rp->cpu->name, rp->os->name);
		break;
	case Tcname:
	case Tmb:
	case Tmd:
	case Tmf:
	case Tns:
		fmtprint(&fstr, "\t%s", rp->host->name);
		break;
	case Tmg:
	case Tmr:
		fmtprint(&fstr, "\t%s", rp->mb->name);
		break;
	case Tminfo:
		fmtprint(&fstr, "\t%s %s", rp->mb->name, rp->rmb->name);
		break;
	case Tmx:
		fmtprint(&fstr, "\t%lud %s", rp->pref, rp->host->name);
		break;
	case Ta:
	case Taaaa:
		fmtprint(&fstr, "\t%s", rp->ip->name);
		break;
	case Tptr:
//		fmtprint(&fstr, "\t%s(%lud)", rp->ptr->name, rp->ptr->ordinal);
		fmtprint(&fstr, "\t%s", rp->ptr->name);
		break;
	case Tsoa:
		fmtprint(&fstr, "\t%s %s %lud %lud %lud %lud %lud", rp->host->name,
			rp->rmb->name, rp->soa->serial, rp->soa->refresh, rp->soa->retry,
			rp->soa->expire, rp->soa->minttl);
		for(s = rp->soa->slaves; s != nil; s = s->next)
			fmtprint(&fstr, " %s", s->name);
		break;
	case Tnull:
		fmtprint(&fstr, "\t%.*H", rp->null->dlen, rp->null->data);
		break;
	case Ttxt:
		fmtprint(&fstr, "\t");
		for(t = rp->txt; t != nil; t = t->next)
			fmtprint(&fstr, "%s", t->p);
		break;
	case Trp:
		fmtprint(&fstr, "\t%s %s", rp->rmb->name, rp->rp->name);
		break;
	case Tkey:
		fmtprint(&fstr, "\t%d %d %d", rp->key->flags, rp->key->proto,
			rp->key->alg);
		break;
	case Tsig:
		fmtprint(&fstr, "\t%d %d %d %lud %lud %lud %d %s",
			rp->sig->type, rp->sig->alg, rp->sig->labels, rp->sig->ttl,
			rp->sig->exp, rp->sig->incep, rp->sig->tag, rp->sig->signer->name);
		break;
	case Tcert:
		fmtprint(&fstr, "\t%d %d %d",
			rp->sig->type, rp->sig->tag, rp->sig->alg);
		break;
	default:
		break;
	}
out:
	strp = fmtstrflush(&fstr);
	rv = fmtstrcpy(f, strp);
	free(strp);
	return rv;
}

/*
 *  print conversion for rr records in attribute value form
 */
int
rravfmt(Fmt *f)
{
	RR *rp;
	char *strp;
	Fmt fstr;
	int rv;
	Server *s;
	Txt *t;
	int quote;

	fmtstrinit(&fstr);

	rp = va_arg(f->args, RR*);
	if(rp == 0){
		fmtprint(&fstr, "<null>");
		goto out;
	}

	if(rp->type == Tptr)
		fmtprint(&fstr, "ptr=%s", rp->owner->name);
	else
		fmtprint(&fstr, "dom=%s", rp->owner->name);

	switch(rp->type){
	case Thinfo:
		fmtprint(&fstr, " cpu=%s os=%s", rp->cpu->name, rp->os->name);
		break;
	case Tcname:
		fmtprint(&fstr, " cname=%s", rp->host->name);
		break;
	case Tmb:
	case Tmd:
	case Tmf:
		fmtprint(&fstr, " mbox=%s", rp->host->name);
		break;
	case Tns:
		fmtprint(&fstr,  " ns=%s", rp->host->name);
		break;
	case Tmg:
	case Tmr:
		fmtprint(&fstr, " mbox=%s", rp->mb->name);
		break;
	case Tminfo:
		fmtprint(&fstr, " mbox=%s mbox=%s", rp->mb->name, rp->rmb->name);
		break;
	case Tmx:
		fmtprint(&fstr, " pref=%lud mx=%s", rp->pref, rp->host->name);
		break;
	case Ta:
	case Taaaa:
		fmtprint(&fstr, " ip=%s", rp->ip->name);
		break;
	case Tptr:
		fmtprint(&fstr, " dom=%s", rp->ptr->name);
		break;
	case Tsoa:
		fmtprint(&fstr, " ns=%s mbox=%s serial=%lud refresh=%lud retry=%lud expire=%lud ttl=%lud",
			rp->host->name, rp->rmb->name, rp->soa->serial,
			rp->soa->refresh, rp->soa->retry,
			rp->soa->expire, rp->soa->minttl);
		for(s = rp->soa->slaves; s != nil; s = s->next)
			fmtprint(&fstr, " dnsslave=%s", s->name);
		break;
	case Tnull:
		fmtprint(&fstr, " null=%.*H", rp->null->dlen, rp->null->data);
		break;
	case Ttxt:
		fmtprint(&fstr, " txt=");
		quote = 0;
		for(t = rp->txt; t != nil; t = t->next)
			if(strchr(t->p, ' '))
				quote = 1;
		if(quote)
			fmtprint(&fstr, "\"");
		for(t = rp->txt; t != nil; t = t->next)
			fmtprint(&fstr, "%s", t->p);
		if(quote)
			fmtprint(&fstr, "\"");
		break;
	case Trp:
		fmtprint(&fstr, " rp=%s txt=%s", rp->rmb->name, rp->rp->name);
		break;
	case Tkey:
		fmtprint(&fstr, " flags=%d proto=%d alg=%d",
			rp->key->flags, rp->key->proto, rp->key->alg);
		break;
	case Tsig:
		fmtprint(&fstr, " type=%d alg=%d labels=%d ttl=%lud exp=%lud incep=%lud tag=%d signer=%s",
			rp->sig->type, rp->sig->alg, rp->sig->labels, rp->sig->ttl,
			rp->sig->exp, rp->sig->incep, rp->sig->tag, rp->sig->signer->name);
		break;
	case Tcert:
		fmtprint(&fstr, " type=%d tag=%d alg=%d",
			rp->sig->type, rp->sig->tag, rp->sig->alg);
		break;
	default:
		break;
	}
out:
	strp = fmtstrflush(&fstr);
	rv = fmtstrcpy(f, strp);
	free(strp);
	return rv;
}

void
warning(char *fmt, ...)
{
	char dnserr[128];
	va_list arg;

	va_start(arg, fmt);
	vseprint(dnserr, dnserr+sizeof(dnserr), fmt, arg);
	va_end(arg);
	syslog(1, "dns", dnserr);
}

/*
 *  create a slave process to handle a request to avoid one request blocking
 *  another
 */
void
slave(Request *req)
{
	static int slaveid;
	int ppid;

	if(req->isslave)
		return;		/* we're already a slave process */

	/*
	 * These calls to putactivity cannot block. 
	 * After getactivity(), the current process is counted
	 * twice in dnvars.active (one will pass to the child).
	 * If putactivity tries to wait for dnvars.active == 0,
	 * it will never happen.
	 */

	/* limit parallelism */
	if(getactivity(req, 1) > Maxactive){
		if(traceactivity) syslog(0, "dns", "[%d] too much activity", getpid());
		putactivity(1);
		return;
	}

	ppid = getpid();
	switch(rfork(RFPROC|RFNOTEG|RFMEM|RFNOWAIT)){
	case -1:
		putactivity(1);
		break;
	case 0:
		if(traceactivity) syslog(0, "dns", "[%d] take activity from %d", ppid, getpid());
		req->isslave = 1;
		break;
	default:
		longjmp(req->mret, 1);
	}
}

/*
 *  chasing down double free's
 */
void
dncheck(void *p, int dolock)
{
	int i;
	DN *dp;
	RR *rp;
	extern Pool *mainmem;

	if(p != nil){
		dp = p;
		assert(dp->magic == DNmagic);
	}

	if(!testing)
		return;

	if(dolock)
		lock(&dnlock);
	poolcheck(mainmem);
	for(i = 0; i < HTLEN; i++)
		for(dp = ht[i]; dp; dp = dp->next){
			assert(dp != p);
			assert(dp->magic == DNmagic);
			for(rp = dp->rr; rp; rp = rp->next){
				assert(rp->magic == RRmagic);
				assert(rp->cached);
				assert(rp->owner == dp);
			}
		}
	if(dolock)
		unlock(&dnlock);
}

static int
rrequiv(RR *r1, RR *r2)
{
	return r1->owner == r2->owner
		&& r1->type == r2->type
		&& r1->arg0 == r2->arg0
		&& r1->arg1 == r2->arg1;
}

void
unique(RR *rp)
{
	RR **l, *nrp;

	for(; rp; rp = rp->next){
		l = &rp->next;
		for(nrp = *l; nrp; nrp = *l){
			if(rrequiv(rp, nrp)){
				*l = nrp->next;
				rrfree(nrp);
			} else
				l = &nrp->next;
		}
	}
}

/*
 *  true if second domain is subsumed by the first
 */
int
subsume(char *higher, char *lower)
{
	int hn, ln;

	ln = strlen(lower);
	hn = strlen(higher);
	if(ln < hn)
		return 0;

	if(cistrcmp(lower + ln - hn, higher) != 0)
		return 0;

	if(ln > hn && hn != 0 && lower[ln - hn - 1] != '.')
		return 0;

	return 1;
}

/*
 *  randomize the order we return items to provide some
 *  load balancing for servers.
 *
 *  only randomize the first class of entries
 */
RR*
randomize(RR *rp)
{
	RR *first, *last, *x, *base;
	ulong n;

	if(rp == nil || rp->next == nil)
		return rp;

	/* just randomize addresses and mx's */
	for(x = rp; x; x = x->next)
		if(x->type != Ta && x->type != Tmx && x->type != Tns)
			return rp;

	base = rp; 

	n = rand();
	last = first = nil;
	while(rp != nil){
		/* stop randomizing if we've moved past our class */
		if(base->auth != rp->auth || base->db != rp->db){
			last->next = rp;
			break;
		}

		/* unchain */
		x = rp;
		rp = x->next;
		x->next = nil;

		if(n&1){
			/* add to tail */
			if(last == nil)
				first = x;
			else
				last->next = x;
			last = x;
		} else {
			/* add to head */
			if(last == nil)
				last = x;
			x->next = first;
			first = x;
		}

		/* reroll the dice */
		n >>= 1;
	}
	return first;
}

static int
sencodefmt(Fmt *f)
{
	char *out;
	char *buf;
	int i, len;
	int ilen;
	int rv;
	uchar *b;
	char obuf[64];	// rsc optimization

	if(!(f->flags&FmtPrec) || f->prec < 1)
		goto error;

	b = va_arg(f->args, uchar*);
	if(b == nil)
		goto error;

	/* if it's a printable, go for it */
	len = f->prec;
	for(i = 0; i < len; i++)
		if(!isprint(b[i]))
			break;
	if(i == len){
		if(len >= sizeof obuf)
			len = sizeof(obuf)-1;
		memmove(obuf, b, len);
		obuf[len] = 0;
		fmtstrcpy(f, obuf);
		return 0;
	}

	ilen = f->prec;
	f->prec = 0;
	f->flags &= ~FmtPrec;
	switch(f->r){
	case '<':
		len = (8*ilen+4)/5 + 3;
		break;
	case '[':
		len = (8*ilen+5)/6 + 4;
		break;
	case 'H':
		len = 2*ilen + 1;
		break;
	default:
		goto error;
	}

	if(len > sizeof(obuf)){
		buf = malloc(len);
		if(buf == nil)
			goto error;
	} else
		buf = obuf;

	// convert
	out = buf;
	switch(f->r){
	case '<':
		rv = enc32(out, len, b, ilen);
		break;
	case '[':
		rv = enc64(out, len, b, ilen);
		break;
	case 'H':
		rv = enc16(out, len, b, ilen);
		break;
	default:
		rv = -1;
		break;
	}
	if(rv < 0)
		goto error;

	fmtstrcpy(f, buf);
	if(buf != obuf)
		free(buf);
	return 0;

error:
	return fmtstrcpy(f, "<encodefmt>");

}

void*
emalloc(int size)
{
	char *x;

	x = mallocz(size, 1);
	if(x == nil)
		abort();
	setmalloctag(x, getcallerpc(&size));
	return x;
}

char*
estrdup(char *s)
{
	int size;
	char *p;

	size = strlen(s)+1;
	p = mallocz(size, 0);
	if(p == nil)
		abort();
	memmove(p, s, size);
	setmalloctag(p, getcallerpc(&s));
	return p;
}

/*
 *  create a pointer record
 */
static RR*
mkptr(DN *dp, char *ptr, ulong ttl)
{
	DN *ipdp;
	RR *rp;

	ipdp = dnlookup(ptr, Cin, 1);

	rp = rralloc(Tptr);
	rp->ptr = dp;
	rp->owner = ipdp;
	rp->db = 1;
	if(ttl)
		rp->ttl = ttl;
	return rp;
}

/*
 *  look for all ip addresses in this network and make
 *  pointer records for them.
 */
void
dnptr(uchar *net, uchar *mask, char *dom, int bytes, int ttl)
{
	int i, j;
	DN *dp;
	RR *rp, *nrp, *first, **l;
	uchar ip[IPaddrlen];
	uchar nnet[IPaddrlen];
	char ptr[Domlen];
	char *p, *e;

	l = &first;
	first = nil;
	for(i = 0; i < HTLEN; i++){
		for(dp = ht[i]; dp; dp = dp->next){
			for(rp = dp->rr; rp; rp = rp->next){
				if(rp->type != Ta || rp->negative)
					continue;
				parseip(ip, rp->ip->name);
				maskip(ip, mask, nnet);
				if(ipcmp(net, nnet) != 0)
					continue;
				p = ptr;
				e = ptr+sizeof(ptr);
				for(j = IPaddrlen-1; j >= IPaddrlen-bytes; j--)
					p = seprint(p, e, "%d.", ip[j]);
				seprint(p, e, "%s", dom);
				nrp = mkptr(dp, ptr, ttl);
				*l = nrp;
				l = &nrp->next;
			}
		}
	}

	for(rp = first; rp != nil; rp = nrp){
		nrp = rp->next;
		rp->next = nil;
		rrattach(rp, 1);
	}
}

void
freeserverlist(Server *s)
{
	Server *next;

	for(; s != nil; s = next){
		next = s->next;
		free(s);
	}
}

void
addserver(Server **l, char *name)
{
	Server *s;

	while(*l)
		l = &(*l)->next;
	s = malloc(sizeof(Server)+strlen(name)+1);
	if(s == nil)
		return;
	s->name = (char*)(s+1);
	strcpy(s->name, name);
	s->next = nil;
	*l = s;
}

Server*
copyserverlist(Server *s)
{
	Server *ns;

	
	for(ns = nil; s != nil; s = s->next)
		addserver(&ns, s->name);
	return ns;
}