code: plan9front

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devvga: fix race condition between writes to vgactl

to reproduce:

	for(i in `{seq 10}) echo softscreen off >/dev/vgactl

--- a/sys/src/9/pc/devvga.c

+++ b/sys/src/9/pc/devvga.c

@@ -280,8 +280,10 @@

 			error("bad channel");

 		if(chantodepth(chan) != z)

 			error("depth, channel do not match");

+		qlock(&drawlock);

 		deletescreenimage();

 		setscreensize(scr, r.max.x, r.max.y, z, chan, scr->tilt);

+		qunlock(&drawlock);

 		return;

 	case CMactualsize:

@@ -296,6 +298,7 @@

 			error(Ebadarg);

 		if(r.max.x > scr->width || r.max.y > scr->height)

 			error("physical screen bigger than virtual");

+		qlock(&drawlock);

 		deletescreenimage();

 		setactualsize(scr, r);

 		goto Resized;

@@ -324,6 +327,7 @@

 		}

 		if(scr->gscreen == nil)

 			return;

+		qlock(&drawlock);

 		r = actualscreensize(scr);

 		chan = scr->gscreen->chan;

 		z = scr->gscreen->depth;

@@ -331,9 +335,11 @@

 		setscreensize(scr, scr->width, scr->height, z, chan, tilt);

 		setactualsize(scr, r);

 		/* no break */

-	case CMdrawinit:

-		if(scr->gscreen == nil)

+	Init:

+		if(scr->gscreen == nil){

+			qunlock(&drawlock);

 			error(Enoscreen);

+		}

 		if(scr->dev && scr->dev->drawinit)

 			scr->dev->drawinit(scr);

 		hwblank = scr->blank != nil;

@@ -341,7 +347,12 @@

 	Resized:

 		vgascreenwin(scr);

 		resetscreenimage();

+		qunlock(&drawlock);

 		return;

+

+	case CMdrawinit:

+		qlock(&drawlock);

+		goto Init;

 	case CMlinear:

 		if(cb->nf!=2 && cb->nf!=3)

--- a/sys/src/9/pc/screen.c

+++ b/sys/src/9/pc/screen.c

@@ -64,17 +64,11 @@

 void

 setactualsize(VGAscr *scr, Rectangle r)

 {

-	qlock(&drawlock);

-

 	r.min = ZP;

 	r.max = tiltsize(scr->tilt, r.max);

-	if(rectclip(&r, scr->gscreen->r) == 0){

-		qunlock(&drawlock);

+	if(rectclip(&r, scr->gscreen->r) == 0)

 		return;

-	}

 	scr->gscreen->clipr = r;

-

-	qunlock(&drawlock);

 }

 static char*

@@ -136,11 +130,8 @@

 {

 	char *err;

-	qlock(&drawlock);

-	if(waserror()){

-		qunlock(&drawlock);

+	if(waserror())

 		nexterror();

-	}

 	if(memimageinit() < 0)

 		error("memimageinit failed");

@@ -169,7 +160,6 @@

 		cursoron();

 	}

-	qunlock(&drawlock);

 	poperror();

 }

--- a/sys/src/9/pc/vga.c

+++ b/sys/src/9/pc/vga.c

@@ -183,8 +183,6 @@

 	Point p;

 	int h;

-	qlock(&drawlock);

-	

 	h = scr->memdefont->height;

 	r = scr->gscreen->r;

@@ -215,11 +213,7 @@

 	curpos = window.min;

 	flushmemscreen(r);

-

-	qunlock(&drawlock);

-

 	vgascreenputs(kmesg.buf, kmesg.n);

-

 	screenputs = vgascreenputs;

 }

--- a/sys/src/9/port/devdraw.c

+++ b/sys/src/9/port/devdraw.c

@@ -949,7 +949,6 @@

 void

 deletescreenimage(void)

 {

-	dlock();

 	if(screenimage){

 		/* will be freed via screendimage; disable */

 		screenimage->clipr = ZR;

@@ -959,15 +958,12 @@

 		drawfreedimage(screendimage);

 		screendimage = nil;

 	}

-	dunlock();

 }

 void

 resetscreenimage(void)

 {

-	dlock();

 	initscreenimage();

-	dunlock();

 }

 static Chan*

--- a/sys/src/9/zynq/screen.c

+++ b/sys/src/9/zynq/screen.c

@@ -299,8 +299,8 @@

 		if(chantodepth(chan) != z)

 			error("depth, channel do not match");

-		deletescreenimage();

 		eqlock(&drawlock);

+		deletescreenimage();

 		if(memimageinit() < 0){

 			qunlock(&drawlock);

 			error("memimageinit failed");

@@ -310,14 +310,18 @@

 			gscreen = nil;

 		}

 		gscreen = allocmemimage(Rect(0,0,x,y), chan);

-		qunlock(&drawlock);

-		/* wet floor */

-

-	case CMinit:

-		if(gscreen == nil)

+	Init:

+		if(gscreen == nil){

+			qunlock(&drawlock);

 			error("no framebuffer");

+		}

 		resetscreenimage();

+		qunlock(&drawlock);

 		break;

+

+	case CMinit:

+		qlock(&drawlock);

+		goto Init;

 	}

 	free(cb);

 	poperror();