ntpd: use MSG_DONTWAIT; better readability

function                                             old     new   delta
gettime_fp                                             -      39     +39
ntpd_main                                           3214    3199     -15
gettime                                               47       -     -47
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 0/1 up/down: 39/-62)            Total: -23 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 108 insertions, 101 deletions

diff --git a/networking/ntpd.c b/networking/ntpd.c
index 4e661ce98..fb82fd309 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -16,7 +16,7 @@
 #define	INTERVAL_QUERY_PATHETIC		60
 #define	INTERVAL_QUERY_AGRESSIVE	5
 
-#define	TRUSTLEVEL_BADPEER		6
+#define	TRUSTLEVEL_BADPEER		6	/* bad if *less than* TRUSTLEVEL_BADPEER */
 #define	TRUSTLEVEL_PATHETIC		2
 #define	TRUSTLEVEL_AGRESSIVE		8
 #define	TRUSTLEVEL_MAX			10
@@ -214,14 +214,13 @@ add_peers(const char *s)
 }
 
 static double
-gettime(void)
+gettime_fp(void)
 {
 	struct timeval tv;
 	gettimeofday(&tv, NULL); /* never fails */
-	return (tv.tv_sec + JAN_1970 + 1.0e-6 * tv.tv_usec);
+	return (tv.tv_sec + 1.0e-6 * tv.tv_usec + JAN_1970);
 }
 
-
 static void
 d_to_tv(double d, struct timeval *tv)
 {
@@ -298,9 +297,9 @@ sendmsg_wrap(int fd,
 
 	errno = 0;
 	if (!from) {
-		ret = sendto(fd, msg, len, 0, to, addrlen);
+		ret = sendto(fd, msg, len, MSG_DONTWAIT, to, addrlen);
 	} else {
-		ret = send_to_from(fd, msg, len, 0, to, from, addrlen);
+		ret = send_to_from(fd, msg, len, MSG_DONTWAIT, to, from, addrlen);
 	}
 	if (ret != len) {
 		bb_perror_msg("send failed");
@@ -310,7 +309,7 @@ sendmsg_wrap(int fd,
 }
 
 static int
-client_query(ntp_peer_t *p)
+send_query_to_peer(ntp_peer_t *p)
 {
 	if (p->query.fd == -1) {
 		p->query.fd = xsocket(p->lsa->u.sa.sa_family, SOCK_DGRAM, 0);
@@ -336,7 +335,7 @@ client_query(ntp_peer_t *p)
 
 	p->query.msg.xmttime.int_partl = random();
 	p->query.msg.xmttime.fractionl = random();
-	p->query.xmttime = gettime();
+	p->query.xmttime = gettime_fp();
 
 	if (sendmsg_wrap(p->query.fd, /*from:*/ NULL, /*to:*/ &p->lsa->u.sa, /*addrlen:*/ p->lsa->len,
 			&p->query.msg, NTP_MSGSIZE_NOAUTH) == -1) {
@@ -377,6 +376,7 @@ adjtime_wrap(void)
 {
 	ntp_peer_t	 *p;
 	unsigned	  offset_cnt;
+	unsigned	  middle;
 	int		  i = 0;
 	ntp_peer_t	**peers;
 	double		  offset_median;
@@ -394,7 +394,10 @@ adjtime_wrap(void)
 		offset_cnt++;
 	}
 
-	peers = xzalloc(sizeof(ntp_peer_t *) * offset_cnt);
+	if (offset_cnt == 0)
+		goto clear_good;
+
+	peers = xzalloc(sizeof(peers[0]) * offset_cnt);
 	for (item = G.ntp_peers; item != NULL; item = item->link) {
 		p = (ntp_peer_t *) item->data;
 		if (p->trustlevel < TRUSTLEVEL_BADPEER)
@@ -402,62 +405,55 @@ adjtime_wrap(void)
 		peers[i++] = p;
 	}
 
-	qsort(peers, offset_cnt, sizeof(ntp_peer_t *), offset_compare);
-
-	if (offset_cnt != 0) {
-		if ((offset_cnt & 1) == 0) {
-//TODO: try offset_cnt /= 2...
-			offset_median =
-			    (peers[offset_cnt / 2 - 1]->update.offset +
-			    peers[offset_cnt / 2]->update.offset) / 2;
-			G.status.rootdelay =
-			    (peers[offset_cnt / 2 - 1]->update.delay +
-			    peers[offset_cnt / 2]->update.delay) / 2;
-			G.status.stratum = MAX(
-			    peers[offset_cnt / 2 - 1]->update.status.stratum,
-			    peers[offset_cnt / 2]->update.status.stratum);
-		} else {
-			offset_median = peers[offset_cnt / 2]->update.offset;
-			G.status.rootdelay = peers[offset_cnt / 2]->update.delay;
-			G.status.stratum = peers[offset_cnt / 2]->update.status.stratum;
-		}
-		G.status.leap = peers[offset_cnt / 2]->update.status.leap;
+	qsort(peers, offset_cnt, sizeof(peers[0]), offset_compare);
 
-		bb_info_msg("adjusting local clock by %fs", offset_median);
+	middle = offset_cnt / 2;
+	if ((offset_cnt & 1) == 0) {
+		offset_median = (peers[middle-1]->update.offset + peers[middle]->update.offset) / 2;
+		G.status.rootdelay = (peers[middle-1]->update.delay + peers[middle]->update.delay) / 2;
+		G.status.stratum = MAX(peers[middle-1]->update.status.stratum, peers[middle]->update.status.stratum);
+	} else {
+		offset_median = peers[middle]->update.offset;
+		G.status.rootdelay = peers[middle]->update.delay;
+		G.status.stratum = peers[middle]->update.status.stratum;
+	}
+	G.status.leap = peers[middle]->update.status.leap;
 
-		d_to_tv(offset_median, &tv);
-		if (adjtime(&tv, &olddelta) == -1)
-			bb_error_msg("adjtime failed");
-		else if (!G.firstadj
-		 && olddelta.tv_sec == 0
-		 && olddelta.tv_usec == 0
-		 && !G.status.synced
-		) {
-			bb_info_msg("clock synced");
-			G.status.synced = 1;
-		} else if (G.status.synced) {
-			bb_info_msg("clock unsynced");
-			G.status.synced = 0;
-		}
+	bb_info_msg("adjusting local clock by %fs", offset_median);
 
-		G.firstadj = 0;
-		G.status.reftime = gettime();
-		G.status.stratum++;	/* one more than selected peer */
-		G.scale = updated_scale(offset_median);
+	d_to_tv(offset_median, &tv);
+	if (adjtime(&tv, &olddelta) == -1)
+		bb_error_msg("adjtime failed");
+	else if (!G.firstadj
+	 && olddelta.tv_sec == 0
+	 && olddelta.tv_usec == 0
+	 && !G.status.synced
+	) {
+		bb_info_msg("clock synced");
+		G.status.synced = 1;
+	} else if (G.status.synced) {
+		bb_info_msg("clock unsynced");
+		G.status.synced = 0;
+	}
+
+	G.firstadj = 0;
+	G.status.reftime = gettime_fp();
+	G.status.stratum++;	/* one more than selected peer */
+	G.scale = updated_scale(offset_median);
 
-		G.status.refid4 = peers[offset_cnt / 2]->update.status.refid4;
+	G.status.refid4 = peers[middle]->update.status.refid4;
 
-		lsa = peers[offset_cnt / 2]->lsa;
-		G.status.refid =
+	lsa = peers[middle]->lsa;
+	G.status.refid =
 #if ENABLE_FEATURE_IPV6
-			lsa->u.sa.sa_family != AF_INET ?
-				G.status.refid4 :
+		lsa->u.sa.sa_family != AF_INET ?
+			G.status.refid4 :
 #endif
-				lsa->u.sin.sin_addr.s_addr;
-	}
+			lsa->u.sin.sin_addr.s_addr;
 
 	free(peers);
 
+ clear_good:
 	for (item = G.ntp_peers; item != NULL; item = item->link) {
 		p = (ntp_peer_t *) item->data;
 		p->update.good = 0;
@@ -514,7 +510,7 @@ settime(double offset)
 }
 
 static void
-client_update(ntp_peer_t *p)
+update_peer_data(ntp_peer_t *p)
 {
 	int i, best = 0, good = 0;
 
@@ -561,7 +557,7 @@ scale_interval(time_t requested)
 }
 
 static void
-client_dispatch(ntp_peer_t *p)
+recv_and_process_peer_pkt(ntp_peer_t *p)
 {
 	char			 *addr;
 	ssize_t			 size;
@@ -572,13 +568,13 @@ client_dispatch(ntp_peer_t *p)
 
 	addr = xmalloc_sockaddr2dotted_noport(&p->lsa->u.sa);
 
-//TODO: use MSG_DONTWAIT flag?
-	size = recv(p->query.fd, &msg, sizeof(msg), 0);
+	size = recv(p->query.fd, &msg, sizeof(msg), MSG_DONTWAIT);
 	if (size == -1) {
 		bb_perror_msg("recv(%s) error", addr);
 		if (errno == EHOSTUNREACH || errno == EHOSTDOWN
 		 || errno == ENETUNREACH || errno == ENETDOWN
 		 || errno == ECONNREFUSED || errno == EADDRNOTAVAIL
+		 || errno == EAGAIN
 		) {
 //TODO: always do this?
 			set_next(p, error_interval());
@@ -587,7 +583,7 @@ client_dispatch(ntp_peer_t *p)
 		xfunc_die();
 	}
 
-	T4 = gettime();
+	T4 = gettime_fp();
 
 	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
 		bb_error_msg("malformed packet received from %s", addr);
@@ -639,6 +635,7 @@ client_dispatch(ntp_peer_t *p)
 		goto bail;
 	}
 	offset->error = (T2 - T1) - (T3 - T4);
+// Can we use (T4 - JAN_1970) instead of time(NULL)?
 	offset->rcvd = time(NULL);
 	offset->good = 1;
 
@@ -664,21 +661,19 @@ client_dispatch(ntp_peer_t *p)
 
 	/* every received reply which we do not discard increases trust */
 	if (p->trustlevel < TRUSTLEVEL_MAX) {
-		if (p->trustlevel < TRUSTLEVEL_BADPEER
-		 && p->trustlevel + 1 >= TRUSTLEVEL_BADPEER
-		) {
-			bb_info_msg("peer %s now valid", addr);
-		}
 		p->trustlevel++;
+		if (p->trustlevel == TRUSTLEVEL_BADPEER)
+			bb_info_msg("peer %s now valid", addr);
 	}
 
 	bb_info_msg("reply from %s: offset %f delay %f, next query %ds", addr,
 			offset->offset, offset->delay, (int) interval);
 
-	client_update(p);
+	update_peer_data(p);
 	settime(offset->offset);
 
-	if (++p->shift >= OFFSET_ARRAY_SIZE)
+	p->shift++;
+	if (p->shift >= OFFSET_ARRAY_SIZE)
 		p->shift = 0;
 
  bail:
@@ -687,7 +682,7 @@ client_dispatch(ntp_peer_t *p)
 
 #if ENABLE_FEATURE_NTPD_SERVER
 static void
-server_dispatch(int fd)
+recv_and_process_client_pkt(void /*int fd*/)
 {
 	ssize_t          size;
 	uint8_t          version;
@@ -702,12 +697,14 @@ server_dispatch(int fd)
 	to = get_sock_lsa(G.listen_fd);
 	from = xzalloc(to->len);
 
-//TODO: use MGS_DONTWAIT flag?
-	size = recv_from_to(fd, &msg, sizeof(msg), 0, from, &to->u.sa, to->len);
+	size = recv_from_to(G.listen_fd, &msg, sizeof(msg), MSG_DONTWAIT, from, &to->u.sa, to->len);
 	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
 		char *addr;
-		if (size < 0)
-			bb_error_msg_and_die("recv_from_to");
+		if (size < 0) {
+			if (errno == EAGAIN)
+				goto bail;
+			bb_perror_msg_and_die("recv_from_to");
+		}
 		addr = xmalloc_sockaddr2dotted_noport(from);
 		bb_error_msg("malformed packet received from %s", addr);
 		free(addr);
@@ -727,18 +724,18 @@ server_dispatch(int fd)
 	msg.stratum = G.status.stratum;
 	msg.ppoll = query_ppoll;
 	msg.precision = G.status.precision;
-	rectime = gettime();
+	rectime = gettime_fp();
 	msg.xmttime = msg.rectime = d_to_lfp(rectime);
 	msg.reftime = d_to_lfp(G.status.reftime);
-	//msg.xmttime = d_to_lfp(gettime()); // = msg.rectime
+	//msg.xmttime = d_to_lfp(gettime_fp()); // = msg.rectime
 	msg.orgtime = query_xmttime;
 	msg.rootdelay = d_to_sfp(G.status.rootdelay);
 	version = (query_status & VERSION_MASK); /* ... >> VERSION_SHIFT - done below instead */
 	msg.refid = (version > (3 << VERSION_SHIFT)) ? G.status.refid4 : G.status.refid;
 
-	/* We reply from the address packet was sent to,
+	/* We reply from the local address packet was sent to,
 	 * this makes to/from look swapped here: */
-	sendmsg_wrap(fd,
+	sendmsg_wrap(G.listen_fd,
 		/*from:*/ &to->u.sa, /*to:*/ from, /*addrlen:*/ to->len,
 		&msg, size);
 
@@ -910,20 +907,23 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
 	ntp_init(argv);
 
 	{
-		unsigned new_cnt = g.peer_cnt;
-		idx2peer = xzalloc(sizeof(void *) * new_cnt);
+		unsigned cnt = g.peer_cnt;
 		/* if ENABLE_FEATURE_NTPD_SERVER, + 1 for listen_fd: */
-		pfd = xzalloc(sizeof(pfd[0]) * (new_cnt + ENABLE_FEATURE_NTPD_SERVER));
+		idx2peer = xzalloc(sizeof(void *) * (cnt + ENABLE_FEATURE_NTPD_SERVER));
+		pfd = xzalloc(sizeof(pfd[0]) * (cnt + ENABLE_FEATURE_NTPD_SERVER));
 	}
 
 	while (!bb_got_signal) {
 		llist_t *item;
-		unsigned i, j, first_peer_idx;
+		unsigned i, j;
 		unsigned sent_cnt, trial_cnt;
 		int nfds, timeout;
-		time_t nextaction;
+		time_t cur_time, nextaction;
 
-		nextaction = time(NULL) + 3600;
+		/* Nothing between here and poll() blocks for any significant time */
+
+		cur_time = time(NULL);
+		nextaction = cur_time + 3600;
 
 		i = 0;
 #if ENABLE_FEATURE_NTPD_SERVER
@@ -933,22 +933,19 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
 			i++;
 		}
 #endif
-		first_peer_idx = i;
+		/* Pass over peer list, send requests, time out on receives */
 		sent_cnt = trial_cnt = 0;
 		for (item = g.ntp_peers; item != NULL; item = item->link) {
 			ntp_peer_t *p = (ntp_peer_t *) item->data;
 
-			if (p->next > 0 && p->next <= time(NULL)) {
+			if (p->next != 0 && p->next <= cur_time) {
+				/* Time to send new req */
 				trial_cnt++;
-				if (client_query(p) == 0)
+				if (send_query_to_peer(p) == 0)
 					sent_cnt++;
 			}
-			if (p->next > 0 && p->next < nextaction)
-				nextaction = p->next;
-			if (p->deadline > 0 && p->deadline < nextaction)
-				nextaction = p->deadline;
-
-			if (p->deadline > 0 && p->deadline <= time(NULL)) {
+			if (p->deadline != 0 && p->deadline <= cur_time) {
+				/* Timed out waiting for reply */
 				char *addr = xmalloc_sockaddr2dotted_noport(&p->lsa->u.sa);
 
 				timeout = error_interval();
@@ -964,39 +961,49 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
 				set_next(p, timeout);
 			}
 
+			if (p->next != 0 && p->next < nextaction)
+				nextaction = p->next;
+			if (p->deadline != 0 && p->deadline < nextaction)
+				nextaction = p->deadline;
+
 			if (p->state == STATE_QUERY_SENT) {
+				/* Wait for reply from this peer */
 				pfd[i].fd = p->query.fd;
 				pfd[i].events = POLLIN;
-				idx2peer[i - first_peer_idx] = p;
+				idx2peer[i] = p;
 				i++;
 			}
 		}
 
 		if ((trial_cnt > 0 && sent_cnt == 0) || g.peer_cnt == 0)
-			settime(0);	/* no good peers, don't wait */
+			settime(0); /* no good peers, don't wait */
 
-		timeout = nextaction - time(NULL);
+		timeout = nextaction - cur_time;
 		if (timeout < 0)
 			timeout = 0;
 
+		/* Here we may block */
 		if (g.verbose)
 			bb_error_msg("entering poll %u secs", timeout);
 		nfds = poll(pfd, i, timeout * 1000);
+		if (nfds <= 0)
+			continue;
 
+		/* Process any received packets */
 		j = 0;
 #if ENABLE_FEATURE_NTPD_SERVER
-//TODO: simplify. There is only one server fd!
-		for (; nfds > 0 && j < first_peer_idx; j++) {
-			if (pfd[j].revents & (POLLIN|POLLERR)) {
+		if (g.listen_fd != -1) {
+			if (pfd[0].revents /* & (POLLIN|POLLERR)*/) {
 				nfds--;
-				server_dispatch(pfd[j].fd);
+				recv_and_process_client_pkt(/*g.listen_fd*/);
 			}
+			j = 1;
 		}
 #endif
-		for (; nfds > 0 && j < i; j++) {
-			if (pfd[j].revents & (POLLIN|POLLERR)) {
+		for (; nfds != 0 && j < i; j++) {
+			if (pfd[j].revents /* & (POLLIN|POLLERR)*/) {
 				nfds--;
-				client_dispatch(idx2peer[j - first_peer_idx]);
+				recv_and_process_peer_pkt(idx2peer[j]);
 			}
 		}
 	} /* while (!bb_got_signal) */