platforms/drm: Introduce KWIN_DRM_DEVICES

This allows to instruct kwin what drm devices must be used explicitly.

BUG: 435467

src/plugins/platforms/drm/drm_backend.cpp

@@ -40,6 +40,7 @@
 #include <QSocketNotifier>
 // system
 #include <algorithm>
+#include <sys/stat.h>
 #include <unistd.h>
 // drm
 #include <xf86drm.h>
@@ -176,9 +177,16 @@ bool DrmBackend::initialize()
     connect(session(), &Session::activeChanged, this, &DrmBackend::activate);
     connect(session(), &Session::awoke, this, &DrmBackend::turnOutputsOn);
 
-    std::vector<UdevDevice::Ptr> devices = m_udev->listGPUs();
-    for (unsigned int gpu_index = 0; gpu_index < devices.size(); gpu_index++) {
-        addGpu(std::move(devices.at(gpu_index)));
+    const QStringList explicitGpus = qEnvironmentVariable("KWIN_DRM_DEVICES").split(':', Qt::SkipEmptyParts);
+    if (!explicitGpus.isEmpty()) {
+        for (const QString &fileName : explicitGpus) {
+            addGpu(fileName);
+        }
+    } else {
+        const auto devices = m_udev->listGPUs();
+        for (const UdevDevice::Ptr &device : devices) {
+            addGpu(device->devNode());
+        }
     }
 
     if (m_gpus.isEmpty()) {
@@ -217,7 +225,7 @@ void DrmBackend::handleUdevEvent()
 
         if (device->action() == QStringLiteral("add")) {
             if (m_gpus.isEmpty() || !primaryGpu()->useEglStreams()) {
-                if (const auto &gpu = addGpu(std::move(device))) {
+                if (const auto &gpu = addGpu(device->devNode())) {
                     updateOutputs();
                     updateCursor();
                     emit gpuAdded(gpu);
@@ -249,24 +257,31 @@ void DrmBackend::handleUdevEvent()
     }
 }
 
-DrmGpu *DrmBackend::addGpu(std::unique_ptr<UdevDevice> device)
+DrmGpu *DrmBackend::addGpu(const QString &fileName)
 {
-    int fd = session()->openRestricted(device->devNode());
+    int fd = session()->openRestricted(fileName);
     if (fd < 0) {
-        qCWarning(KWIN_DRM) << "failed to open drm device at" << device->devNode();
+        qCWarning(KWIN_DRM) << "failed to open drm device at" << fileName;
         return nullptr;
     }
 
     // try to make a simple drm get resource call, if it fails it is not useful for us
     drmModeRes *resources = drmModeGetResources(fd);
     if (!resources) {
-        qCDebug(KWIN_DRM) << "Skipping KMS incapable drm device node at" << device->devNode();
+        qCDebug(KWIN_DRM) << "Skipping KMS incapable drm device node at" << fileName;
         session()->closeRestricted(fd);
         return nullptr;
     }
     drmModeFreeResources(resources);
 
-    DrmGpu *gpu = new DrmGpu(this, device->devNode(), fd, device->devNum());
+    struct stat buf;
+    if (fstat(fd, &buf) == -1) {
+        qCDebug(KWIN_DRM, "Failed to fstat %s: %s", qPrintable(fileName), strerror(errno));
+        session()->closeRestricted(fd);
+        return nullptr;
+    }
+
+    DrmGpu *gpu = new DrmGpu(this, fileName, fd, buf.st_rdev);
     if (!gpu->useEglStreams() || m_gpus.isEmpty()) {
         m_gpus.append(gpu);
         m_active = true;

src/plugins/platforms/drm/drm_backend.h

@@ -92,7 +92,7 @@ private:
     void writeOutputsConfiguration();
     QString generateOutputConfigurationUuid() const;
     void handleUdevEvent();
-    DrmGpu *addGpu(std::unique_ptr<UdevDevice> device);
+    DrmGpu *addGpu(const QString &fileName);
 
     QScopedPointer<Udev> m_udev;
     QScopedPointer<UdevMonitor> m_udevMonitor;

src/plugins/platforms/drm/drm_gpu.cpp

@@ -36,7 +36,7 @@
 namespace KWin
 {
 
-DrmGpu::DrmGpu(DrmBackend *backend, QByteArray devNode, int fd, dev_t deviceId)
+DrmGpu::DrmGpu(DrmBackend *backend, const QString &devNode, int fd, dev_t deviceId)
     : m_backend(backend)
     , m_devNode(devNode)
     , m_fd(fd)

src/plugins/platforms/drm/drm_gpu.h

@@ -34,7 +34,7 @@ class DrmGpu : public QObject
 {
     Q_OBJECT
 public:
-    DrmGpu(DrmBackend *backend, QByteArray devNode, int fd, dev_t deviceId);
+    DrmGpu(DrmBackend *backend, const QString &devNode, int fd, dev_t deviceId);
     ~DrmGpu();
 
     // getters
@@ -58,7 +58,7 @@ public:
         return m_useEglStreams;
     }
 
-    QByteArray devNode() const {
+    QString devNode() const {
         return m_devNode;
     }
 
@@ -118,7 +118,7 @@ private:
     DrmBackend* const m_backend;
     AbstractEglBackend *m_eglBackend;
 
-    const QByteArray m_devNode;
+    const QString m_devNode;
     QSize m_cursorSize;
     const int m_fd;
     const dev_t m_deviceId;

src/plugins/platforms/fbdev/fb_backend.cpp

@@ -103,14 +103,14 @@ bool FramebufferBackend::initialize()
 {
     setSoftwareCursorForced(true);
 
-    QByteArray framebufferDevice = deviceIdentifier();
+    QString framebufferDevice = deviceIdentifier();
     if (framebufferDevice.isEmpty()) {
         const auto fbs = Udev().listFramebuffers();
         if (fbs.size() > 0) {
             framebufferDevice = fbs.at(0)->devNode();
         }
     }
-    int fd = open(framebufferDevice.constData(), O_RDWR | O_CLOEXEC);
+    int fd = open(framebufferDevice.toUtf8().constData(), O_RDWR | O_CLOEXEC);
     qCDebug(KWIN_FB) << "Using frame buffer device:" << framebufferDevice;
     if (fd < 0) {
         qCWarning(KWIN_FB) << "failed to open frame buffer device:" << framebufferDevice;

src/udev.cpp

@@ -208,9 +208,9 @@ UdevDevice::~UdevDevice()
     udev_device_unref(m_device);
 }
 
-const char *UdevDevice::devNode()
+QString UdevDevice::devNode() const
 {
-    return udev_device_get_devnode(m_device);
+    return QString::fromUtf8(udev_device_get_devnode(m_device));
 }
 
 dev_t UdevDevice::devNum() const

src/udev.h

@@ -30,7 +30,7 @@ public:
     UdevDevice(udev_device *device);
     ~UdevDevice();
 
-    const char *devNode();
+    QString devNode() const;
     dev_t devNum() const;
     const char *property(const char *key);
     bool hasProperty(const char *key, const char *value);