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ndb/dns: remove procname statistics and restart feature, cleanup 9p service loop

given that the memory leaks have been fixed, theres no need
for the obscure restart feature which is not reliable anyway.

remove the code updating procname on each 9p request.

handle convM2S error by exiting the service loop, dont read
9p channel after eof.

--- a/sys/src/cmd/ndb/dns.c

+++ b/sys/src/cmd/ndb/dns.c

@@ -25,8 +25,6 @@

 int vers;		/* incremented each clone/attach */

-static volatile int stop;

-

 /* holds data to be returned via read of /net/dns, perhaps multiple reads */

 struct Mfile

 {

@@ -113,7 +111,6 @@

 void

 main(int argc, char *argv[])

 {

-	int kid, pid;

 	char servefile[Maxpath], ext[Maxpath];

 	Dir *dir;

@@ -205,32 +202,14 @@

 	if (cfg.straddle && !seerootns())

 		dnslog("straddle server misconfigured; can't see root name servers");

-	/*

-	 * fork without sharing heap.

-	 * parent waits around for child to die, then forks & restarts.

-	 * child may spawn udp server, notify procs, etc.; when it gets too

-	 * big, it kills itself and any children.

-	 * /srv/dns and /net/dns remain open and valid.

-	 */

-	for (;;) {

-		kid = rfork(RFPROC|RFFDG|RFNOTEG);

-		switch (kid) {

-		case -1:

-			sysfatal("fork failed: %r");

-		case 0:

-			if(cfg.serve)

-				dnudpserver(mntpt);

-			if(sendnotifies)

-				notifyproc();

-			io();

-			_exits("restart");

-		default:

-			while ((pid = waitpid()) != kid && pid != -1)

-				continue;

-			break;

-		}

-		dnslog("dns restarting");

-	}

+

+	if(cfg.serve)

+		dnudpserver(mntpt);

+	if(sendnotifies)

+		notifyproc();

+

+	io();

+	_exits(0);

 }

 /*

@@ -275,9 +254,9 @@

 	/* copy namespace to avoid a deadlock */

 	switch(rfork(RFFDG|RFPROC|RFNAMEG)){

-	case 0:			/* child: hang around and (re)start main proc */

+	case 0:			/* child: start main proc */

 		close(p[1]);

-		procsetname("%s restarter", mntpt);

+		procsetname("%s", mntpt);

 		break;

 	case -1:

 		sysfatal("fork failed: %r");

@@ -417,23 +396,19 @@

 	if(setjmp(req.mret))

 		putactivity(0);

 	req.isslave = 0;

-	stop = 0;

-	while(!stop){

-		procsetname("%d %s/dns Twrites of %d 9p rpcs read; %d alarms",

-			stats.qrecvd9p, mntpt, stats.qrecvd9prpc, stats.alarms);

-		while((n = read9pmsg(mfd[0], mdata, sizeof mdata)) == 0)

-			;

+	while((n = read9pmsg(mfd[0], mdata, sizeof mdata)) != 0){

 		if(n < 0){

 			dnslog("error reading 9P from %s: %r", mntpt);

-			sleep(2000);	/* don't thrash after read error */

-			return;

+			break;

 		}

 		stats.qrecvd9prpc++;

 		job = newjob();

 		if(convM2S(mdata, n, &job->request) != n){

+			dnslog("format error %ux %ux %ux %ux %ux",

+				mdata[0], mdata[1], mdata[2], mdata[3], mdata[4]);

 			freejob(job);

-			continue;

+			break;

 		}

 		mf = newfid(job->request.fid, 0);

 		if(debug)

@@ -501,9 +476,6 @@

 		putactivity(0);

 	}

-	/* kill any udp server, notifier, etc. processes */

-	postnote(PNGROUP, getpid(), "die");

-	sleep(1000);

 }

 void

@@ -726,8 +698,6 @@

 		dndump("/lib/ndb/dnsdump");

 	else if(strcmp(job->request.data, "refresh")==0)

 		needrefresh = 1;

-	else if(strcmp(job->request.data, "restart")==0)

-		stop = 1;

 	else if(strcmp(job->request.data, "stats")==0)

 		dnstats("/lib/ndb/dnsstats");

 	else if(strncmp(job->request.data, "target ", 7)==0){