Disable the DRM master hooks when EGLFS isn't used

app/app.pro

@@ -317,6 +317,7 @@ libdrm {
     linux {
         !disable-masterhooks {
             message(Master hooks enabled)
+            DEFINES += HAVE_DRM_MASTER_HOOKS
             SOURCES += masterhook.c masterhook_internal.c
             LIBS += -ldl -pthread
         }

app/main.cpp

@@ -85,6 +85,10 @@ static QAtomicInteger<uint64_t> s_LogBytesWritten = 0;
 static QFile* s_LoggerFile;
 #endif
 
+#ifdef HAVE_DRM_MASTER_HOOKS
+extern "C" bool g_DisableDrmHooks;
+#endif
+
 class LoggerTask : public QRunnable
 {
 public:
@@ -789,6 +793,11 @@ int main(int argc, char *argv[])
     }
 #endif
 
+#ifdef HAVE_DRM_MASTER_HOOKS
+    // Only use the Qt-SDL DRM master interoperability hooks if Qt is using KMS
+    g_DisableDrmHooks = QGuiApplication::platformName() != "eglfs";
+#endif
+
 #ifdef STEAM_LINK
     // Qt 5.9 from the Steam Link SDK is not able to load any fonts
     // since the Steam Link doesn't include any of the ones it looks

app/masterhook.c

@@ -28,6 +28,9 @@
 #include <xf86drm.h>
 #include <xf86drmMode.h>
 
+// Used to turn off the hooks when Qt is not using EGLFS
+bool g_DisableDrmHooks = false;
+
 // We require SDL 2.0.15+ to hook because it supports sharing
 // the DRM FD with our code. This avoids having multiple DRM FDs
 // in flight at the same time which would significantly complicate
@@ -90,6 +93,10 @@ int drmModeSetCrtc(int fd, uint32_t crtcId, uint32_t bufferId,
     // Lookup the real libdrm function pointers if we haven't yet
     pthread_once(&s_InitDrmFunctions, lookupRealDrmFunctions);
 
+    if (g_DisableDrmHooks) {
+        return fn_drmModeSetCrtc(fd, crtcId, bufferId, x, y, connectors, count, mode);
+    }
+
     // Grab the first DRM Master FD that makes it in here. This will be the Qt
     // EGLFS backend's DRM FD, on which we will call drmDropMaster() later.
     if (g_QtDrmMasterFd == -1 && drmIsMaster(fd)) {
@@ -128,7 +135,7 @@ int drmModePageFlip(int fd, uint32_t crtc_id, uint32_t fb_id, uint32_t flags, vo
 
     // Call into the real thing
     int err = fn_drmModePageFlip(fd, crtc_id, fb_id, flags, user_data);
-    if (err == -EACCES && fd == g_QtDrmMasterFd) {
+    if (!g_DisableDrmHooks && err == -EACCES && fd == g_QtDrmMasterFd) {
         // If SDL took master from us, try to grab it back temporarily
         int oldMasterFd = takeMasterFromSdlFd();
         drmSetMaster(fd);
@@ -148,6 +155,10 @@ int drmModeAtomicCommit(int fd, drmModeAtomicReqPtr req,
     // Lookup the real libdrm function pointers if we haven't yet
     pthread_once(&s_InitDrmFunctions, lookupRealDrmFunctions);
 
+    if (g_DisableDrmHooks) {
+        return fn_drmModeAtomicCommit(fd, req, flags, user_data);
+    }
+
     // Grab the first DRM Master FD that makes it in here. This will be the Qt
     // EGLFS backend's DRM FD, on which we will call drmDropMaster() later.
     if (g_QtDrmMasterFd == -1 && drmIsMaster(fd)) {
@@ -210,6 +221,10 @@ int close(int fd)
     // Lookup the real libc functions if we haven't yet
     pthread_once(&s_InitLibCFunctions, lookupRealLibCFunctions);
 
+    if (g_DisableDrmHooks) {
+        return fn_close(fd);
+    }
+
     // Remove this entry from the SDL FD table
     bool lastSdlFd = removeSdlFd(fd);
 

app/masterhook_internal.c

@@ -31,6 +31,7 @@
 
 extern int g_QtDrmMasterFd;
 extern struct stat g_DrmMasterStat;
+extern bool g_DisableDrmHooks;
 
 #define MAX_SDL_FD_COUNT 8
 int g_SdlDrmMasterFds[MAX_SDL_FD_COUNT];
@@ -114,6 +115,10 @@ int openHook(typeof(open) *real_open, typeof(close) *real_close, const char *pat
         fd = real_open(pathname, flags);
     }
 
+    if (g_DisableDrmHooks) {
+        return fd;
+    }
+
     // If the file was successfully opened and we have a DRM master FD,
     // check if the FD we just opened is a DRM device.
     if (fd >= 0 && g_QtDrmMasterFd != -1) {