From 8fa6c5307b46e8ee855581569c9a9efd8ff91c7c Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Sat, 3 Jun 2023 12:16:33 +0300
Subject: [PATCH] backends/drm: Reopen the drm node

GEM handles are not reference counted and are unique per drm file
descriptor.

With the upcoming changes, dmabuf and dumb buffers will be abstraced
using DmaBufAttributes.

The issue with it is that we need GEM handles to get a drm framebuffer.
drmPrimeFDToHandle() can be used to get the GEM handle for a drm file
descriptor, but we would hit the reference counting issues then and
potentially double close GEM handles.

In order to resolve that, this change makes the drm backend reopen the
drm node to get a new GEM handle namespace for rendering.
---
 src/backends/drm/drm_gpu.cpp | 11 ++++++++++-
 src/backends/drm/drm_gpu.h   |  1 +
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/backends/drm/drm_gpu.cpp b/src/backends/drm/drm_gpu.cpp
index dbb3b7fed9..8b4f013e9d 100644
--- a/src/backends/drm/drm_gpu.cpp
+++ b/src/backends/drm/drm_gpu.cpp
@@ -78,7 +78,15 @@ DrmGpu::DrmGpu(DrmBackend *backend, const QString &devNode, int fd, dev_t device
     m_isNVidia = strstr(version->name, "nvidia-drm");
     m_isVirtualMachine = strstr(version->name, "virtio") || strstr(version->name, "qxl")
         || strstr(version->name, "vmwgfx") || strstr(version->name, "vboxvideo");
-    m_gbmDevice = gbm_create_device(m_fd);
+
+    // Reopen the drm node to create a new GEM handle namespace.
+    m_gbmFd = FileDescriptor{open(devNode.toLocal8Bit(), O_RDWR | O_CLOEXEC)};
+    if (m_gbmFd.isValid()) {
+        drm_magic_t magic;
+        drmGetMagic(m_gbmFd.get(), &magic);
+        drmAuthMagic(m_fd, magic);
+        m_gbmDevice = gbm_create_device(m_gbmFd.get());
+    }
 
     m_socketNotifier = std::make_unique<QSocketNotifier>(fd, QSocketNotifier::Read);
     connect(m_socketNotifier.get(), &QSocketNotifier::activated, this, &DrmGpu::dispatchEvents);
@@ -102,6 +110,7 @@ DrmGpu::~DrmGpu()
     if (m_gbmDevice) {
         gbm_device_destroy(m_gbmDevice);
     }
+    m_gbmFd = FileDescriptor{};
     m_platform->session()->closeRestricted(m_fd);
 }
 
diff --git a/src/backends/drm/drm_gpu.h b/src/backends/drm/drm_gpu.h
index cfac2c5097..574c4af5b3 100644
--- a/src/backends/drm/drm_gpu.h
+++ b/src/backends/drm/drm_gpu.h
@@ -139,6 +139,7 @@ private:
     bool m_isActive = true;
     clockid_t m_presentationClock;
     gbm_device *m_gbmDevice;
+    FileDescriptor m_gbmFd;
     std::unique_ptr<EglDisplay> m_eglDisplay;
     DrmBackend *const m_platform;