gamescope only offers LINEAR dmabufs, which the EGL/GL interop path can't handle (NVIDIA's
EGL lists no LINEAR modifier for sampling). Attempt a direct CUDA external-memory import
(cuImportExternalMemory OPAQUE_FD, cached per buffer fd, one DtoD copy per frame into the
pooled buffer): the FFI + plumbing are in place, and LINEAR(0) is now advertised alongside
the tiled EGL modifiers (tiled first, so KWin still prefers it — regression-tested).
Empirically the 595 desktop driver rejects raw dmabuf fds as OPAQUE_FD (CUDA_ERROR_UNKNOWN),
matching the documented limitation — true LINEAR GPU import needs a Vulkan interop bridge
(import dmabuf via VK_EXT_external_memory_dma_buf, GPU-copy into an exportable allocation,
hand that to CUDA), noted as future work. So the importer now degrades instead of dying:
on GPU-import failure it logs once, disables itself, and falls through to the CPU mmap path.
Validated: gamescope + LUMEN_ZEROCOPY=1 runs full-rate (122.9 fps @720p120, valid HEVC) via
the fallback; KWin keeps real zero-copy.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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