From ada2d0d0700b7b49e0455b39980e012630cd4801 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Fri, 8 Jun 1990 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1990-06-08

---
 power/dat.h     |  3 ++-
 power/devbit3.c | 61 ++++++++++++++++++++++++++++++++++---------------
 2 files changed, 44 insertions(+), 20 deletions(-)

diff --git a/power/dat.h b/power/dat.h
index 61b6809a0f143dd3fd9e1139679c0c19c1a6a38c..90a8abc2391c5890b11af82f30134c27c6a768ba 100644
--- a/power/dat.h
+++ b/power/dat.h
@@ -345,7 +345,8 @@ struct User
 	 * I/O point for bit3 interface.  This is the easiest way to allocate
 	 * them, but not the prettiest or most general.
 	 */
-	Bit3msg	bit3;
+	Bit3msg	kbit3;
+	Bit3msg	ubit3;
 	/*
 	 * Rest of structure controlled by devproc.c and friends.
 	 * lock(&p->debug) to modify.
diff --git a/power/devbit3.c b/power/devbit3.c
index f4e7f46d90fef2fa5024e0836de46e95f5fa63b7..6f8fcecd65df6fc5a78964a1270f2d3d5861e66e 100644
--- a/power/devbit3.c
+++ b/power/devbit3.c
@@ -11,6 +11,7 @@
 static struct
 {
 	QLock;
+	QLock	buflock;
 	int	open;
 	char	buf[10*1024];
 }bit3;
@@ -89,7 +90,7 @@ bit3open(Chan *c, int omode)
 {
 	Bit3msg *bp;
 
-	bp = &((User*)(u->p->upage->pa|KZERO))->bit3;
+	bp = &((User*)(u->p->upage->pa|KZERO))->kbit3;
 	if(c->qid!=1 || omode!=ORDWR)
 		error(0, Eperm);
 	qlock(&bit3);
@@ -134,26 +135,40 @@ bit3read(Chan *c, void *buf, long n)
 	Bit3msg *bp;
 	int docpy;
 
-	bp = &((User*)(u->p->upage->pa|KZERO))->bit3;
-	bp->rcount = 0;
 	switch(c->qid){
 	case 1:
 		if(n > sizeof bit3.buf)
 			error(0, Egreg);
-		docpy = 0;
-		qlock(&bit3);
-		if((((ulong)buf)&(KSEGM|3)) == KSEG0)
+		if((((ulong)buf)&(KSEGM|3)) == KSEG0){
+			/*
+			 *  use supplied buffer, no need to lock for reply
+			 */
+			bp = &((User*)(u->p->upage->pa|KZERO))->kbit3;
+			bp->rcount = 0;
+			qlock(&bit3);
 			bit3send(bp, READ, buf, n);
-		else{
+			qunlock(&bit3);
+			do
+				n = bp->rcount;
+			while(n == 0);
+		}else{
+			/*
+			 *  use bit3 buffer.  lock the buffer till the reply
+			 */
+			bp = &((User*)(u->p->upage->pa|KZERO))->ubit3;
+			bp->rcount = 0;
+			qlock(&bit3.buflock);
+
+			qlock(&bit3);
 			bit3send(bp, READ, bit3.buf, n);
-			docpy = 1;
-		}
-		qunlock(&bit3);
-		do
-			n = bp->rcount;
-		while(n == 0);
-		if(docpy)
+			qunlock(&bit3);
+			do
+				n = bp->rcount;
+			while(n == 0);
 			memcpy(buf, bit3.buf, n);
+
+			qunlock(&bit3.buflock);
+		}
 		return n;
 	}
 	error(0, Egreg);
@@ -165,19 +180,27 @@ bit3write(Chan *c, void *buf, long n)
 {
 	Bit3msg *bp;
 
-	bp = &((User*)(u->p->upage->pa|KZERO))->bit3;
 	switch(c->qid){
 	case 1:
 		if(n > sizeof bit3.buf)
 			error(0, Egreg);
-		qlock(&bit3);
-		if((((ulong)buf)&(KSEGM|3)) == KSEG0)
+		if((((ulong)buf)&(KSEGM|3)) == KSEG0){
+			bp = &((User*)(u->p->upage->pa|KZERO))->kbit3;
+			qlock(&bit3);
 			bit3send(bp, WRITE, buf, n);
-		else{
+			qunlock(&bit3);
+		}else{
+			bp = &((User*)(u->p->upage->pa|KZERO))->ubit3;
+			qlock(&bit3.buflock);
+
+			qlock(&bit3);
 			memcpy(bit3.buf, buf, n);
 			bit3send(bp, WRITE, bit3.buf, n);
+			do; while(*BIT3ADDR);
+			qunlock(&bit3);
+
+			qunlock(&bit3.buflock);
 		}
-		qunlock(&bit3);
 		return n;
 	}
 	error(0, Egreg);