Fail loudly on a touch read, stop the workers before their sockets close, and file down the small edges

fb.go

@@ -170,23 +170,24 @@ func findDisplay(fd int) (connID, crtcID uint32, err error) {
 }
 
 // The card number is not stable across machines, so the card driving a
-// connected display is the one we want.
-func openCard() (int, error) {
+// connected display is the one we want, and the display it found comes back
+// with it.
+func openCard() (fd int, connID, crtcID uint32, err error) {
 	paths, err := filepath.Glob("/dev/dri/card*")
 	if err != nil {
-		return -1, err
+		return -1, 0, 0, err
 	}
 	for _, p := range paths {
 		fd, err := unix.Open(p, unix.O_RDWR|unix.O_CLOEXEC, 0)
 		if err != nil {
 			continue
 		}
-		if _, _, err := findDisplay(fd); err == nil {
-			return fd, nil
+		if connID, crtcID, err := findDisplay(fd); err == nil {
+			return fd, connID, crtcID, nil
 		}
 		unix.Close(fd)
 	}
-	return -1, fmt.Errorf("no drm device with a connected display")
+	return -1, 0, 0, fmt.Errorf("no drm device with a connected display")
 }
 
 func (fb *framebuffer) addScanout(i int) error {
@@ -223,7 +224,7 @@ func (fb *framebuffer) addScanout(i int) error {
 }
 
 func openFramebuffer() (*framebuffer, error) {
-	fd, err := openCard()
+	fd, connID, crtcID, err := openCard()
 	if err != nil {
 		return nil, err
 	}
@@ -236,11 +237,6 @@ func openFramebuffer() (*framebuffer, error) {
 		return nil, fmt.Errorf("take drm master: %w", err)
 	}
 
-	connID, crtcID, err := findDisplay(fd)
-	if err != nil {
-		fb.close()
-		return nil, err
-	}
 	mode, err := preferredMode(fd, connID)
 	if err != nil {
 		fb.close()

input.go

@@ -119,8 +119,11 @@ func watchTouch(w, h int) (*touchState, error) {
 		var down bool
 		for {
 			n, err := f.Read(buf)
+			// Nothing else feeds this state, so returning here would freeze the
+			// last touch in place and leave the reset button dead while the panel
+			// goes on looking alive.
 			if err != nil {
-				return
+				panic(fmt.Sprintf("reading touchscreen events: %v", err))
 			}
 			for o := 0; o+sizeofInputEvent <= n; o += sizeofInputEvent {
 				typ := *(*uint16)(unsafe.Pointer(&buf[o+16]))
@@ -142,9 +145,11 @@ func watchTouch(w, h int) (*touchState, error) {
 					if code != synReport {
 						break
 					}
+					// Scaled onto [0, w-1], so full deflection is the last pixel
+					// rather than one past it.
 					state.set(
-						int(int64(rawX-minX)*int64(w)/int64(maxX-minX)),
-						int(int64(rawY-minY)*int64(h)/int64(maxY-minY)),
+						int(int64(rawX-minX)*int64(w-1)/int64(maxX-minX)),
+						int(int64(rawY-minY)*int64(h-1)/int64(maxY-minY)),
 						down)
 				}
 			}

main.go

@@ -640,6 +640,20 @@ func run(aName, bName string, nsPerM float64) error {
 		defer wg.Done()
 		samp.run(&done, startTx)
 	}()
+	// Every return from here on stops the workers before the deferred closes
+	// pull their sockets out from under them: otherwise the sampler panics on a
+	// closed fd and can mask the error that actually ended the run. An error
+	// before the gate opens closes it here, or the wait would hang on
+	// goroutines still parked at startTx.
+	defer func() {
+		done.Store(true)
+		select {
+		case <-startTx:
+		default:
+			close(startTx)
+		}
+		wg.Wait()
+	}()
 	rxReady.Wait()
 
 	sig := make(chan os.Signal, 1)
@@ -674,8 +688,6 @@ func run(aName, bName string, nsPerM float64) error {
 	for {
 		select {
 		case <-sig:
-			done.Store(true)
-			wg.Wait()
 			return nil
 		case <-space:
 			start = resetAll(dirs, stats)

probe.go

@@ -170,10 +170,13 @@ func (p *probeSender) awaitTx(scratch, oob []byte) (int64, bool) {
 	fds := []unix.PollFd{{Fd: int32(p.fd), Events: unix.POLLERR}}
 	deadline := time.Now().Add(probeTimeout)
 	for {
-		ms := int(time.Until(deadline).Milliseconds())
-		if ms <= 0 {
+		left := time.Until(deadline)
+		if left <= 0 {
 			return 0, false
 		}
+		// Rounded up, since truncating would give up with time still on the
+		// clock and shave the last fraction of a millisecond off every wait.
+		ms := int((left + time.Millisecond - 1) / time.Millisecond)
 		n, err := unix.Poll(fds, ms)
 		if err == unix.EINTR {
 			continue

render.go

@@ -75,8 +75,10 @@ func commas(v uint64) string {
 // on the label. Below a thousand no letter is left dangling, since a trailing
 // space would push the figure off centre.
 func scaleSI(v float64) string {
+	// %.2f rounds 999.995 and up to a fourth digit, so the magnitude rolls over
+	// where the rounding does rather than at the bare thousand.
 	for _, mag := range []string{"", "k", "M", "G", "T"} {
-		if v < 1000 {
+		if v < 999.995 {
 			if mag == "" {
 				return fmt.Sprintf("%.2f", v)
 			}