From 585e2325b33c067dabe84f9940a8d5e4aa4968f7 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Tue, 9 Mar 1993 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1993-03-09

---
 port/devproc.c | 35 +++++++++++++++++++++++++++++++++--
 port/portdat.h |  1 +
 port/portfns.h |  1 +
 port/proc.c    | 13 ++++++++++++-
 4 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/port/devproc.c b/port/devproc.c
index 464736a76b32d24e4f9357dc43190bc13250a2ff..ed22d0fab2ac4b48655a984ff71cdcc8d80422c3 100644
--- a/port/devproc.c
+++ b/port/devproc.c
@@ -18,6 +18,7 @@ enum{
 	Qsegment,
 	Qstatus,
 	Qtext,
+	Qwait,
 };
 
 #define	STATSIZE	(2*NAMELEN+12+7*12)
@@ -31,6 +32,7 @@ Dirtab procdir[] =
 	"segment",	{Qsegment},	0,			0444,
 	"status",	{Qstatus},	STATSIZE,		0444,
 	"text",		{Qtext},	0,			0000,
+	"wait",		{Qwait},	0,			0400,
 };
 
 /* Segment type from portdat.h */
@@ -157,8 +159,6 @@ procopen(Chan *c, int omode)
 
 	switch(QID(c->qid)){
 	case Qtext:
-		if(omode != OREAD)
-			error(Eperm);
 		tc = proctext(c, p);
 		tc->offset = 0;
 		return tc;
@@ -169,6 +169,7 @@ procopen(Chan *c, int omode)
 	case Qsegment:
 	case Qproc:
 	case Qstatus:
+	case Qwait:
 		break;
 
 	case Qnotepg:
@@ -243,6 +244,7 @@ procread(Chan *c, void *va, long n, ulong offset)
 	long l;
 	User *up;
 	Segment *sg;
+	Waitq *wq;
 
 	if(c->qid.path & CHDIR)
 		return devdirread(c, a, n, 0, 0, procgen);
@@ -383,6 +385,35 @@ procread(Chan *c, void *va, long n, ulong offset)
 			exhausted("segments");
 		memmove(a, &statbuf[offset], n);
 		return n;
+
+	case Qwait:
+		if(n < sizeof(Waitmsg))
+			error(Etoosmall);
+
+		if(!canqlock(&p->qwaitr))
+			error(Einuse);
+
+		if(waserror()) {
+			qunlock(&p->qwaitr);
+			nexterror();
+		}
+
+		lock(&p->exl);
+		while(p->waitq == 0) {
+			unlock(&p->exl);
+			sleep(&p->waitr, haswaitq, p);
+			lock(&p->exl);
+		}
+		wq = p->waitq;
+		p->waitq = wq->next;
+		p->nwait--;
+		unlock(&p->exl);
+
+		qunlock(&p->qwaitr);
+		poperror();
+		memmove(a, &wq->w, sizeof(Waitmsg));
+		free(wq);
+		return sizeof(Waitmsg);
 	}
 	error(Egreg);
 	return 0;		/* not reached */
diff --git a/port/portdat.h b/port/portdat.h
index d4f714f58b410f811f399eab8d5ec175a474a992..24242c8af9e4373713b345ac354b1cedcea8c7cf 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -576,6 +576,7 @@ struct Proc
 	Waitq	*waitq;			/* Exited processes wait children */
 	int	nchild;			/* Number of living children */
 	int	nwait;			/* Number of uncollected wait records */
+	QLock	qwaitr;
 	Rendez	waitr;			/* Place to hang out in wait */
 	Proc	*parent;
 
diff --git a/port/portfns.h b/port/portfns.h
index bd723dd897321fabf8d97964f21885397eb4eeeb..782dff32e3b20d66782945d523d4c907c22765c9 100644
--- a/port/portfns.h
+++ b/port/portfns.h
@@ -83,6 +83,7 @@ Block*		getq(Queue*);
 int		gets(IOQ*, void*, int);
 void		gotolabel(Label*);
 Block*		grabq(Queue*);
+int		haswaitq(void*);
 int		hwcursmove(int, int);
 int		hwcursset(uchar*, uchar*, int, int);
 long		ibrk(ulong, int);
diff --git a/port/proc.c b/port/proc.c
index 6cbbcadd465fc3963c88f6bb6508e49a8fde6fe4..eb08a3e88b87d09d1a8fb8ad85f40576b20f00f1 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -590,7 +590,7 @@ pexit(char *exitstr, int freemem)
 			p->waitq = wq;
 			p->nwait++;
 			unlock(&p->exl);
-	
+
 			wakeup(&p->waitr);
 		}
 		else {
@@ -652,6 +652,14 @@ pwait(Waitmsg *w)
 
 	p = u->p;
 
+	if(!canqlock(&p->qwaitr))
+		error(Einuse);
+
+	if(waserror()) {
+		qunlock(&p->qwaitr);
+		nexterror();
+	}
+
 	lock(&p->exl);
 	if(p->nchild == 0 && p->waitq == 0) {
 		unlock(&p->exl);
@@ -667,6 +675,9 @@ pwait(Waitmsg *w)
 	p->nwait--;
 	unlock(&p->exl);
 
+	qunlock(&p->qwaitr);
+	poperror();
+
 	if(w)
 		memmove(w, &wq->w, sizeof(Waitmsg));
 	cpid = atoi(wq->w.pid);