feat: add cuDF C FFI

Cargo.toml

@@ -26,6 +26,7 @@ members = [
     "vortex-duckdb",
     "vortex-cuda",
     "vortex-cuda/cub",
+    "vortex-cuda/ffi",
     "vortex-cuda/gpu-scan-cli",
     "vortex-cuda/macros",
     "vortex-cuda/nvcomp",

vortex-cuda/ffi/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "vortex-cuda-ffi"
+description = "Native C FFI bindings for Vortex CUDA interop"
+readme = "README.md"
+publish = false
+version = { workspace = true }
+homepage = { workspace = true }
+repository = { workspace = true }
+authors = { workspace = true }
+license = { workspace = true }
+keywords = { workspace = true }
+include = { workspace = true }
+edition = { workspace = true }
+rust-version = { workspace = true }
+categories = { workspace = true }
+
+[dependencies]
+arrow-schema = { workspace = true, features = ["ffi"] }
+futures = { workspace = true, features = ["executor"] }
+vortex = { workspace = true, features = ["object_store"] }
+vortex-cuda = { path = ".." }
+vortex-ffi = { path = "../../vortex-ffi" }
+
+[dev-dependencies]
+vortex-array = { workspace = true, features = ["_test-harness"] }
+vortex-cuda-macros = { workspace = true }
+
+[lib]
+name = "vortex_cuda_ffi"
+crate-type = ["rlib", "staticlib", "cdylib"]
+
+[lints]
+workspace = true

vortex-cuda/ffi/README.md

@@ -0,0 +1,16 @@
+# vortex-cuda-ffi
+
+CUDA-specific C FFI helpers for cuDF interop.
+
+This crate keeps CUDA out of the base `vortex-ffi` crate. Its public C API exports a borrowed `vx_array` as an `ArrowSchema + ArrowDeviceArray` pair.
+
+It does not create cuDF objects itself. The caller passes the exported Arrow Device structs to cuDF and releases them after cuDF is done importing.
+
+Use this crate as the CUDA-enabled FFI artifact. Include both headers:
+
+```c
+#include "vortex.h"
+#include "vortex_cuda.h"
+```
+
+and link the CUDA FFI library (`vortex_cuda_ffi`). Do not pass Vortex handles between independently linked Rust FFI libraries.

vortex-cuda/ffi/cinclude/vortex_cuda.h

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright the Vortex contributors
+#pragma once
+
+#include <stdint.h>
+
+#include "vortex.h"
+
+/* Link against the CUDA-enabled FFI library that provides both the base Vortex FFI and these CUDA
+ * entry points. Do not pass Vortex handles between independently linked Rust FFI libraries. */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef USE_OWN_ARROW_DEVICE
+typedef int32_t ArrowDeviceType;
+#define ARROW_DEVICE_CPU 1
+#define ARROW_DEVICE_CUDA 2
+#define ARROW_DEVICE_CUDA_HOST 3
+#define ARROW_DEVICE_OPENCL 4
+#define ARROW_DEVICE_VULKAN 7
+#define ARROW_DEVICE_METAL 8
+#define ARROW_DEVICE_VPI 9
+#define ARROW_DEVICE_ROCM 10
+#define ARROW_DEVICE_ROCM_HOST 11
+#define ARROW_DEVICE_EXT_DEV 12
+#define ARROW_DEVICE_CUDA_MANAGED 13
+#define ARROW_DEVICE_ONEAPI 14
+#define ARROW_DEVICE_WEBGPU 15
+#define ARROW_DEVICE_HEXAGON 16
+
+struct ArrowDeviceArray {
+    struct ArrowArray array;
+    int64_t device_id;
+    ArrowDeviceType device_type;
+    void *sync_event;
+    int64_t reserved[3];
+};
+#endif
+
+typedef struct vx_cuda_error vx_cuda_error;
+
+/**
+ * Return the message for a CUDA FFI error.
+ *
+ * The returned pointer is valid until `error` is freed with `vx_cuda_error_free`.
+ */
+const char *vx_cuda_error_get_message(const vx_cuda_error *error);
+
+/** Free a CUDA FFI error. */
+void vx_cuda_error_free(vx_cuda_error *error);
+
+/**
+ * Export a borrowed Vortex array for cuDF's Arrow Device import path.
+ *
+ * On success, returns 0 and writes independently releasable `out_schema` and `out_array` values.
+ * This function does not create a cuDF object; the caller passes these outputs to cuDF and releases
+ * both with their embedded Arrow callbacks after cuDF is done importing.
+ *
+ * Guarantees:
+ * - `out_array->device_type == ARROW_DEVICE_CUDA`.
+ * - `out_array->device_id` identifies the CUDA device for every exported buffer.
+ * - Struct arrays export as table-shaped schemas; non-struct arrays export as column fields.
+ * - Schema/layout remapping matches Vortex's CUDA exporter, including decimals and lists.
+ *
+ * On error, returns 1 and writes `error_out` when it is not NULL.
+ */
+int vx_cuda_array_export_arrow_device(const vx_session *session,
+                                      const vx_array *array,
+                                      FFI_ArrowSchema *out_schema,
+                                      struct ArrowDeviceArray *out_array,
+                                      vx_cuda_error **error_out);
+
+
+#ifdef __cplusplus
+}
+#endif