qt: shutdown backend on backend shutdown to release devices

Our hidraw udev rule:

```
KERNEL=="hidraw*", SUBSYSTEM=="hidraw", ATTRS{idVendor}=="03eb",
ATTRS{idProduct}=="2403", TAG+="uaccess", TAG+="udev-acl",
SYMLINK+="bitbox02-%n"
```

creates `/dev/bitbox02-N` symlinks (one per HID interface).

The BitBoxApp uses libusb (default backend of karalabe/hid), not
hidraw. However, when a device is opened, the corresponding symlink is
removed, and restored when it is closed (presumably to ensure
exclusive access). Howewer, we never closed the opened devices when
the app closed, leading to the symlink being missing afterwards. This
resulted in apps that use hidraw not being able to connect after the
BitBoxApp connected first, like Sparrow.

This commit calls the backend shutdown on app close, also closing the
opened devices.

Author: benma

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 # 4.47.1
 - Linux: fix support for Wayland
+- Linux: release device upon app close, enabling other apps to connect to the BitBox after the BitBoxApp closes
 
 # 4.47.0
 - Bundle BitBox02 firmware version v9.22.0

backend/backend.go

@@ -898,6 +898,11 @@ func (backend *Backend) Environment() Environment {
 
 // Close shuts down the backend. After this, no other method should be called.
 func (backend *Backend) Close() error {
+	backend.ratesUpdater.Stop()
+	// Call this without `accountsAndKeystoreLock` as it eventually calls `DeregisterKeystore()`,
+	// which acquires the same lock.
+	backend.usbManager.Close()
+
 	defer backend.accountsAndKeystoreLock.Lock()()
 
 	errors := []string{}

backend/bridgecommon/bridgecommon.go

@@ -363,8 +363,9 @@ func Shutdown() {
 
 	log := logging.Get().WithGroup("server")
 	if globalShutdown != nil {
+		log.Info("Shutdown about to be called")
 		globalShutdown()
-		log.Info("Shutdown called")
+		log.Info("Shutdown finished")
 	} else {
 		log.Info("Shutdown called, but backend not running")
 	}

backend/devices/usb/manager.go

@@ -91,6 +91,7 @@ type Manager struct {
 	onUnregister func(string)
 
 	updateCh chan struct{}
+	quitCh   chan struct{}
 
 	socksProxy socksproxy.SocksProxy
 
@@ -118,6 +119,7 @@ func NewManager(
 		onRegister:        onRegister,
 		onUnregister:      onUnregister,
 		updateCh:          make(chan struct{}),
+		quitCh:            make(chan struct{}),
 		socksProxy:        socksProxy,
 
 		log: logging.Get().WithGroup("manager"),
@@ -272,6 +274,14 @@ func (manager *Manager) Update() {
 func (manager *Manager) listen() {
 	for {
 		select {
+		case <-manager.quitCh:
+			return
+		default:
+		}
+
+		select {
+		case <-manager.quitCh:
+			return
 		case <-manager.updateCh:
 		case <-time.After(time.Second):
 		}
@@ -336,3 +346,15 @@ func (manager *Manager) Start() {
 	go manager.listen()
 	manager.Update()
 }
+
+// Close closes and unregisters all devices.
+func (manager *Manager) Close() {
+	manager.log.Info("Closing devices manager")
+	close(manager.quitCh)
+	for deviceID, device := range manager.devices {
+		manager.log.WithField("device-id", deviceID).Info("manager: closing device")
+		device.Close()
+		delete(manager.devices, deviceID)
+		manager.onUnregister(deviceID)
+	}
+}

frontends/qt/libserver.h

@@ -49,7 +49,7 @@ extern void handleURI(cchar_t* uri);
 extern void serve(cppHeapFree cppHeapFreeFn, pushNotificationsCallback pushNotificationsFn, responseCallback responseFn, notifyUserCallback notifyUserFn, cchar_t* preferredLocale, getSaveFilenameCallback getSaveFilenameFn);
 extern void systemOpen(cchar_t* url);
 extern void goLog(cchar_t* msg);
-
+extern void backendShutdown();
 #ifdef __cplusplus
 }
 #endif

frontends/qt/main.cpp

@@ -460,6 +460,7 @@ int main(int argc, char *argv[])
         delete view;
         view = nullptr;
         webClassMutex.unlock();
+        backendShutdown();
     });
 
 #if defined(_WIN32)

frontends/qt/server/server.go

@@ -206,6 +206,11 @@ func goLog(msg *C.cchar_t) {
 	logging.Get().WithGroup("qt-frontend").Info(goMsg)
 }
 
+//export backendShutdown
+func backendShutdown() {
+	bridgecommon.Shutdown()
+}
+
 func authResult(ok bool) {
 	bridgecommon.AuthResult(ok)
 }