From cc7c6340905c8929e7c40ae6723e279c9cc6adf0 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Sat, 1 Aug 1998 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1998-08-01

---
 ip/rudp.c | 71 +++++++++++++++++++++++++++++++++++++++++++------------
 ip/udp.c  |  3 +--
 2 files changed, 57 insertions(+), 17 deletions(-)

diff --git a/ip/rudp.c b/ip/rudp.c
index 6f2981e82df0fe659c6be69d5130c834e2854c0a..2ec802699a986b034de3669ecd797007a59f2ddc 100644
--- a/ip/rudp.c
+++ b/ip/rudp.c
@@ -14,6 +14,15 @@
 #define DEBUG	0
 #define DPRINT if(DEBUG)print
 
+#define SEQDIFF(a,b) ( (a)>=(b)?\
+			(a)-(b):\
+			0xffffffffUL-((b)-(a)) )
+#define INSEQ(a,start,end) ( (start)<=(end)?\
+				((a)>(start)&&(a)<=(end)):\
+				((a)>(start)||(a)<=(end)) )
+#define UNACKED(r) SEQDIFF(r->sndseq, r->ackrcvd)
+#define NEXTSEQ(a) ( (a)+1 == 0 ? 1 : (a)+1 )
+
 enum
 {
 	UDP_HDRSIZE	= 20,	/* pseudo header + udp header */
@@ -27,7 +36,7 @@ enum
 	Rudprxms	= 200,
 	Rudptickms	= 100,
 	Rudpmaxxmit	= 10,
-
+	Maxunacked	= 100,
 };
 
 typedef struct Udphdr Udphdr;
@@ -93,7 +102,7 @@ struct Reliable
 {
 	Reliable *next;
 
-	uchar addr[IPaddrlen];	/* always V6 when put here */
+	uchar	addr[IPaddrlen];	/* always V6 when put here */
 	ushort	port;
 
 	Block	*unacked;	/* unacked msg list */
@@ -110,6 +119,11 @@ struct Reliable
 
 	ulong	acksent;	/* last ack sent */
 	ulong	ackrcvd;	/* last msg for which ack was rcvd */
+
+	/* flow control */
+	QLock	lock;
+	Rendez	vous;
+	int	blocked;
 };
 
 
@@ -185,8 +199,17 @@ rudpconnect(Conv *c, char **argv, int argc)
 static int
 rudpstate(Conv *c, char *state, int n)
 {
-	USED(c);
-	return snprint(state, n, "%s", "Reliable UDP V0.1");
+	Rudpcb *ucb;
+	Reliable *r;
+	int m;
+
+	m = snprint(state, n, "%s", c->inuse?"Open":"Closed");
+	ucb = (Rudpcb*)c->ptcl;
+	qlock(ucb);
+	for(r = ucb->r; r; r = r->next)
+		m += snprint(state+m, n-m, " %I/%d", r->addr, UNACKED(r));
+	qunlock(ucb);
+	return m;
 }
 
 static char*
@@ -238,6 +261,12 @@ rudpclose(Conv *c)
 	unlock(c);
 }
 
+int
+flow(Reliable *r)
+{
+	return UNACKED(r) <= Maxunacked;
+}
+
 void
 rudpkick(Conv *c, int)
 {
@@ -339,14 +368,14 @@ rudpkick(Conv *c, int)
 
 	qlock(ucb);
 	r = relstate(ucb, raddr, rport, "kick");
-	r->sndseq++;
+	r->sndseq = NEXTSEQ(r->sndseq);
 	hnputl(rh->relseq, r->sndseq);
 	hnputl(rh->relsgen, r->sndgen);
 
 	hnputl(rh->relack, r->rcvseq);  /* ACK last rcvd packet */
 	hnputl(rh->relagen, r->rcvgen);
 
-	if(r->rcvseq < r->acksent)
+	if(r->rcvseq != r->acksent)
 		r->acksent = r->rcvseq;
 
 	hnputs(uh->udpcksum, ptclcsum(bp, UDP_IPHDR, dlen+UDP_RHDRSIZE));
@@ -360,6 +389,15 @@ rudpkick(Conv *c, int)
 		r->sndseq, r->sndgen, r->rcvseq, r->rcvgen, r->sndgen);
 
 	ipoput(f, bp, 0, c->ttl);
+
+	/* flow control of sorts */
+	qlock(&r->lock);
+	if(UNACKED(r) > Maxunacked){
+		r->blocked = 1;
+		sleep(&r->vous, flow, r);
+		r->blocked = 0;
+	}
+	qunlock(&r->lock);
 }
 
 void
@@ -664,7 +702,7 @@ loop:
 				if(r->timeout > Rudprxms*r->xmits)
 					relrexmit(c, r);
 			}
-			if(r->acksent < r->rcvseq)
+			if(r->acksent != r->rcvseq)
 				relsendack(c, r);
 		}
 		qunlock(ucb);
@@ -736,7 +774,6 @@ reliput(Conv *c, Block *bp, uchar *addr, ushort port)
 	ack = nhgetl(rh->relack);
 	agen = nhgetl(rh->relagen);
 
-
 	upriv = c->p->priv;
 	ucb = (Rudpcb*)c->ptcl;
 	r = relstate(ucb, addr, port, "input");
@@ -748,16 +785,20 @@ reliput(Conv *c, Block *bp, uchar *addr, ushort port)
 	/* dequeue acked packets */
 	if(ack && agen == r->sndgen){
 		ackreal = 0;
-		while(r->unacked != nil && ack > r->ackrcvd){
+		while(r->unacked != nil && INSEQ(ack, r->ackrcvd, r->sndseq)){
 			nbp = r->unacked;
 			r->unacked = nbp->list;
 			DPRINT("%d/%d acked, r->sndgen = %d\n", 
 			       ack, agen, r->sndgen);
 			freeb(nbp);
-			r->ackrcvd++;
+			r->ackrcvd = NEXTSEQ(r->ackrcvd);
 			ackreal = 1;
 		}
 
+		/* flow control */
+		if(UNACKED(r) < Maxunacked/8 && r->blocked)
+			wakeup(&r->vous);
+
 		/*
 		 *  retransmit next packet if the acked packet
 		 *  was transmitted more than once
@@ -777,7 +818,6 @@ reliput(Conv *c, Block *bp, uchar *addr, ushort port)
 		if(seq != 1)
 			return -1;
 
-
 		/* new connection */
 		if(r->rcvgen != 0){
 			DPRINT("new con r->rcvgen = %d, sgen = %d\n", r->rcvgen, sgen);
@@ -786,8 +826,8 @@ reliput(Conv *c, Block *bp, uchar *addr, ushort port)
 		r->rcvgen = sgen;
 	}
 
-	/* no message */
-	if(seq == 0)
+	/* no message or input queue full */
+	if(seq == 0 || qfull(c->rq))
 		return -1;
 
 	if(DEBUG && ++drop == drop_rate){
@@ -797,9 +837,9 @@ reliput(Conv *c, Block *bp, uchar *addr, ushort port)
 	}
 
 	/* refuse out of order delivery */
-	if(seq != r->rcvseq + 1){
+	if(seq != NEXTSEQ(r->rcvseq)){
 		upriv->orders++;
-		DPRINT("out of sequence %d not %d\n", seq, r->rcvseq + 1);
+		DPRINT("out of sequence %d not %d\n", seq, NEXTSEQ(r->rcvseq));
 		return -1;
 	}
 	r->rcvseq = seq;
@@ -880,6 +920,7 @@ relhangup(Conv *, Reliable *r)
 	r->ackrcvd = 0;
 	r->xmits = 0;
 	r->timeout = 0;
+	wakeup(&r->vous);
 }
 
 /*
diff --git a/ip/udp.c b/ip/udp.c
index 660d178af4fa6c086de58b6011ffbe726e788d6e..474241d97faaaea15799a36c59d1973b42a1fbc6 100644
--- a/ip/udp.c
+++ b/ip/udp.c
@@ -91,8 +91,7 @@ udpconnect(Conv *c, char **argv, int argc)
 static int
 udpstate(Conv *c, char *state, int n)
 {
-	USED(c);
-	return snprint(state, n, "%s", "Datagram");
+	return snprint(state, n, "%s", c->inuse?"Open":"Closed");
 }
 
 static char*