From fe68274bb8cac7ae435a941858cd312124d49016 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Sun, 10 Sep 1995 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1995-09-10

---
 pc/clock.c     |   1 +
 port/devcons.c | 106 ++++++++++++++++++++++++++++++++++++++++++++++++-
 port/portdat.h |   1 +
 port/portfns.h |   1 +
 port/proc.c    |   4 +-
 5 files changed, 111 insertions(+), 2 deletions(-)

diff --git a/pc/clock.c b/pc/clock.c
index 95c66e5078906f964de973115085f18116b519a3..3c6592acbabbe5c4ff1ad9288b2dcb619334f225 100644
--- a/pc/clock.c
+++ b/pc/clock.c
@@ -44,6 +44,7 @@ clock(Ureg *ur, void *arg)
 	hardclock();
 	uartclock();
 	mouseclock();
+	randomclock();
 
 	if(up && up->state == Running){
 		if(anyready())
diff --git a/port/devcons.c b/port/devcons.c
index 455a731e4c31383c47b09ecea8ddfaf44753c714..902b0a1fb155a914fdf5e377e86c64a5f7776502 100644
--- a/port/devcons.c
+++ b/port/devcons.c
@@ -27,9 +27,11 @@ static struct
 	int	ctlpoff;
 } kbd;
 
-
 char	sysname[NAMELEN];
 
+static ulong randomread(uchar*, ulong);
+static void randomreset(void);
+
 void
 printinit(void)
 {
@@ -330,6 +332,7 @@ enum{
 	Qpgrpid,
 	Qpid,
 	Qppid,
+	Qrandom,
 	Qswap,
 	Qsysname,
 	Qsysstat,
@@ -356,6 +359,7 @@ Dirtab consdir[]={
 	"pgrpid",	{Qpgrpid},	NUMSIZE,	0444,
 	"pid",		{Qpid},		NUMSIZE,	0444,
 	"ppid",		{Qppid},	NUMSIZE,	0444,
+	"random",	{Qrandom},	0,		0664,
 	"swap",		{Qswap},	0,		0664,
 	"sysname",	{Qsysname},	0,		0664,
 	"sysstat",	{Qsysstat},	0,		0666,
@@ -406,6 +410,7 @@ readstr(ulong off, char *buf, ulong n, char *str)
 void
 consreset(void)
 {
+	randomreset();
 }
 
 void
@@ -642,6 +647,9 @@ consread(Chan *c, void *buf, long n, ulong offset)
 	case Qsysname:
 		return readstr(offset, buf, n, sysname);
 
+	case Qrandom:
+		return randomread(buf, n);
+
 	default:
 		print("consread %lux\n", c->qid);
 		error(Egreg);
@@ -879,3 +887,99 @@ setterm(char *f)
 	sprint(buf, f, conffile);
 	ksetenv("terminal", buf);
 }
+
+static struct
+{
+	QLock;
+	Rendez	r;
+	uchar	buf[4096];
+	uchar	*ep;
+	uchar	*rp;
+	uchar	*wp;
+	uchar	next;
+	uchar	bits;
+	uchar	wakeme;
+} rb;
+
+ulong randomcount;
+
+void
+randomreset(void)
+{
+	rb.ep = rb.buf + sizeof(rb.buf);
+	rb.rp = rb.wp = rb.buf;
+}
+
+/*
+ *  produce random bits in a circular buffer
+ */
+void
+randomclock(void)
+{
+	int i;
+	uchar *p;
+
+	i = rb.rp - rb.wp;
+	if(i == 1 || i == (1 - sizeof(rb.buf)))
+		return;
+
+	rb.bits = (rb.bits<<2) ^ randomcount;
+	rb.next += 2;
+	if(rb.next != 8)
+		return;
+
+	rb.next = 0;
+	*rb.wp ^= rb.bits;
+	p = rb.wp+1;
+	if(p == rb.ep)
+		p = rb.buf;
+	rb.wp = p;
+
+	if(rb.wakeme)
+		wakeup(&rb.r);
+}
+
+static int
+notempty(void*)
+{
+	return rb.wp != rb.rp;
+}
+
+/*
+ *  consume random bytes from a circular buffer
+ */
+static ulong
+randomread(uchar *p, ulong n)
+{
+	int i, sofar;
+	uchar *e;
+
+	if(waserror()){
+		qunlock(&rb);
+		nexterror();
+	}
+
+	qlock(&rb);
+	for(sofar = 0; sofar < n; sofar += i){
+		i = rb.wp - rb.rp;
+		if(i == 0){
+			rb.wakeme = 1;
+			sleep(&rb.r, notempty, 0);
+			rb.wakeme = 0;
+			continue;
+		}
+		if(i < 0)
+			i = rb.ep - rb.rp;
+		if(i > n)
+			i = n;
+		memmove(p + sofar, rb.rp, i);
+		e = rb.rp + i;
+		if(e == rb.ep)
+			e = rb.buf;
+		rb.rp = e;
+	}
+	qunlock(&rb);
+	poperror();
+
+	return n;
+}
diff --git a/port/portdat.h b/port/portdat.h
index 282b3f9d84cb74222d2bd2d5a6dea2b9267180a5..ffd35fae23cfeee1040db2133a8b501f0efab2b8 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -704,3 +704,4 @@ extern int nsyscall;
 extern Physseg physseg[];
 extern ulong crasharea;
 extern ulong crashend;
+extern ulong randomcount;
diff --git a/port/portfns.h b/port/portfns.h
index 631c0642dcee438eb4cfc35891f7ff3a59ab7f8d..d026f815a5fe981ac3ba95c37dd48d4181193fa0 100644
--- a/port/portfns.h
+++ b/port/portfns.h
@@ -216,6 +216,7 @@ long		qiwrite(Queue*, void*, int);
 long		qwrite(Queue*, void*, int);
 void		qsetlimit(Queue*, int);
 void		qnoblock(Queue*, int);
+void		randomclock(void);
 int		readnum(ulong, char*, ulong, ulong, int);
 int		readstr(ulong, char*, ulong, char*);
 void		ready(Proc*);
diff --git a/port/proc.c b/port/proc.c
index d387e1aaa1bda50e6f597d705a9d34226635afc9..c8fd00b6afb07f5aa432c5c84186f6a4da4bed55 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -47,6 +47,8 @@ char *statename[] =
 	"Rendez",
 };
 
+ulong randomcount;
+
 /*
  * Always splhi()'ed.
  */
@@ -183,7 +185,7 @@ loop:
 	 *  or one that hasn't moved in a while (load balancing).
 	 */
 	spllo();
-	for(;;){
+	for(randomcount++;;randomcount++){
 		/*
 		 *  Once a second we look for a long waiting process
 		 *  in the lowest priority queue to make sure nothing