drm: Follow symlinks for AQ_DRM_DEVICES (#34)

src/backend/drm/DRM.cpp

@@ -8,6 +8,8 @@
 #include <thread>
 #include <deque>
 #include <cstring>
+#include <filesystem>
+#include <system_error>
 #include <sys/mman.h>
 #include <fcntl.h>
 
@@ -135,6 +137,22 @@ static std::vector<SP<CSessionDevice>> scanGPUs(SP<CBackend> backend) {
         backend->log(AQ_LOG_DEBUG, std::format("drm: Explicit device list {}", explicitGpus));
         Hyprutils::String::CVarList explicitDevices(explicitGpus, 0, ':', true);
 
+        // Iterate over GPUs and canonicalize the paths
+        for (auto& d : explicitDevices) {
+          std::error_code ec;
+
+          auto canonicalFilePath = std::filesystem::canonical(d, ec);
+
+          // If there is an error, log and continue.
+          // TODO: Verify that the path is a valid DRM device. (https://gitlab.freedesktop.org/wlroots/wlroots/-/blob/master/backend/session/session.c?ref_type=heads#L369-387)
+          if (ec) {
+              backend->log(AQ_LOG_ERROR, std::format("drm: Failed to canonicalize path {}", d));
+              continue;
+          }
+
+          d = canonicalFilePath.string();
+        }
+
         for (auto& d : explicitDevices) {
             bool found = false;
             for (auto& vd : devices) {