platforms/drm: Ignore udev events while session is inactive

While the session is inactive, the drm master permissions are revoked.
Therefore, we cannot perform things such as modesetting, etc. It also
makes no sense to create or destroy DrmOutput objects.

CCBUG: 435941

src/plugins/platforms/drm/drm_backend.cpp

@@ -158,8 +158,6 @@ void DrmBackend::reactivate()
             // only relevant in atomic mode
             o->m_modesetRequested = true;
             o->m_crtc->blank(o);
-            o->showCursor();
-            o->moveCursor();
         }
     }
 
@@ -169,6 +167,11 @@ void DrmBackend::reactivate()
     if (Compositor *compositor = Compositor::self()) {
         compositor->addRepaintFull();
     }
+
+    // While the session had been inactive, an output could have been added or
+    // removed, we need to re-scan outputs.
+    updateOutputs();
+    updateCursor();
 }
 
 void DrmBackend::deactivate()
@@ -247,27 +250,7 @@ bool DrmBackend::initialize()
         const int fd = m_udevMonitor->fd();
         if (fd != -1) {
             QSocketNotifier *notifier = new QSocketNotifier(fd, QSocketNotifier::Read, this);
-            connect(notifier, &QSocketNotifier::activated, this,
-                [this] {
-                    while (auto device = m_udevMonitor->getDevice()) {
-                        bool drm = false;
-                        for (auto gpu : m_gpus) {
-                            if (gpu->drmId() == device->sysNum()) {
-                                drm = true;
-                                break;
-                            }
-                        }
-                        if (!drm) {
-                            return;
-                        }
-                        if (device->hasProperty("HOTPLUG", "1")) {
-                            qCDebug(KWIN_DRM) << "Received hot plug event for monitored drm device";
-                            updateOutputs();
-                            updateCursor();
-                        }
-                    }
-                }
-            );
+            connect(notifier, &QSocketNotifier::activated, this, &DrmBackend::handleUdevEvent);
             m_udevMonitor->enable();
         }
     }
@@ -275,12 +258,33 @@ bool DrmBackend::initialize()
     return true;
 }
 
+void DrmBackend::handleUdevEvent()
+{
+    while (auto device = m_udevMonitor->getDevice()) {
+        if (!session()->isActive()) {
+            continue;
+        }
+
+        bool drm = false;
+        for (auto gpu : m_gpus) {
+            if (gpu->drmId() == device->sysNum()) {
+                drm = true;
+                break;
+            }
+        }
+        if (!drm) {
+            continue;
+        }
+        if (device->hasProperty("HOTPLUG", "1")) {
+            qCDebug(KWIN_DRM) << "Received hot plug event for monitored drm device";
+            updateOutputs();
+            updateCursor();
+        }
+    }
+}
+
 void DrmBackend::addOutput(DrmOutput *o)
 {
-    if (!m_active) {
-        o->renderLoop()->inhibit();
-    }
-
     m_outputs.append(o);
     m_enabledOutputs.append(o);
     emit o->gpu()->outputEnabled(o);

src/plugins/platforms/drm/drm_backend.h

@@ -103,6 +103,7 @@ private:
     QString generateOutputConfigurationUuid() const;
     DrmOutput *findOutput(quint32 connector);
     void updateOutputsEnabled();
+    void handleUdevEvent();
     QScopedPointer<Udev> m_udev;
     QScopedPointer<UdevMonitor> m_udevMonitor;
     Session *m_session = nullptr;