monitor: centralize solitary and scanout eligibility checks

1 files changed, 49 insertions, 0 deletions

diff --git a/src/helpers/Drm.cpp b/src/helpers/Drm.cpp
index 207b5e3d..f91c5692 100644
--- a/src/helpers/Drm.cpp
+++ b/src/helpers/Drm.cpp
@@ -1,7 +1,50 @@
 #include <xf86drm.h>
+#include <array>
+#include <map>
+#include <mutex>
+#include <optional>
+#include <sys/stat.h>
 #include "Drm.hpp"
 
+namespace {
+    using SDRMNodePair = std::array<dev_t, 2>;
+
+    std::optional<SDRMNodePair> getDrmNodePair(int fd1, int fd2) {
+        const auto DEVA = DRM::devIDFromFD(fd1);
+        const auto DEVB = DRM::devIDFromFD(fd2);
+        if (!DEVA || !DEVB)
+            return std::nullopt;
+
+        SDRMNodePair pair = {*DEVA, *DEVB};
+        if (pair[0] > pair[1])
+            std::swap(pair[0], pair[1]);
+
+        return pair;
+    }
+}
+
+std::optional<dev_t> DRM::devIDFromFD(int fd) {
+    struct stat stat = {};
+    if (fstat(fd, &stat) != 0 || !S_ISCHR(stat.st_mode))
+        return std::nullopt;
+
+    return stat.st_rdev;
+}
+
 bool DRM::sameGpu(int fd1, int fd2) {
+    if (fd1 >= 0 && fd1 == fd2)
+        return true;
+
+    static std::mutex                   cacheMutex;
+    static std::map<SDRMNodePair, bool> sameGpuCache;
+
+    const auto                          NODEPAIR = getDrmNodePair(fd1, fd2);
+    if (NODEPAIR) {
+        std::scoped_lock lock(cacheMutex);
+        if (const auto it = sameGpuCache.find(*NODEPAIR); it != sameGpuCache.end())
+            return it->second;
+    }
+
     drmDevice* devA = nullptr;
     drmDevice* devB = nullptr;
 
@@ -16,5 +59,11 @@ bool DRM::sameGpu(int fd1, int fd2) {
 
     drmFreeDevice(&devA);
     drmFreeDevice(&devB);
+
+    if (NODEPAIR) {
+        std::scoped_lock lock(cacheMutex);
+        sameGpuCache[*NODEPAIR] = same;
+    }
+
     return same;
 }