The missing zero-copy path is closed. NVIDIA's EGL won't sample LINEAR and the CUDA driver
rejects raw dmabuf fds — but Vulkan imports dmabufs (VK_EXT_external_memory_dma_buf) and
exports OPAQUE_FD memory that CUDA officially imports. zerocopy/vulkan.rs (ash):
dmabuf fd → VkBuffer (import cached per fd) → vkCmdCopyBuffer (GPU) →
exportable VkBuffer → vkGetMemoryFdKHR(OPAQUE_FD) → cuImportExternalMemory → CUdeviceptr
The exportable buffer + CUDA mapping are per-resolution; per frame it's one GPU buffer copy
(fence-waited) + one pitched CUDA copy into the encoder's pool. No CPU touches pixels.
EglImporter::import_linear now routes through the bridge (lazy init; any failure still falls
back to the CPU mmap path). cuda::ExternalDmabuf gained import_owned_fd for the
Vulkan-exported fd.
Validated live: gamescope 720p120 → "Vulkan→CUDA exportable staging buffer ready
size=3686400" (exactly 1280*720*4), full-rate 122.7 fps, decoded frame pixel-correct
(vkcube). KWin's tiled EGL path regression-tested intact. NV12 negotiation dropped — moot
now that BGRx is fully zero-copy.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
826da9968e