feat: add fabric-bridge node for RDMA/inter-host MXL flow sharing

- New fabric-bridge node: initiator mode reads local MXL flow and
  transfers via Fabrics (RDMA/TCP); target mode receives remote data
  and commits to local MXL flow writer
- Add set_mxl_instance/get_mxl_instance to Node base class
- CMake option DMF_BUILD_FABRICS=OFF by default (needs libfabric)
- Target publishes target_info in status for out-of-band exchange
- Initiator receives target_info via config parameter

nodes/fabric-bridge/CMakeLists.txt

@@ -0,0 +1,28 @@
+cmake_minimum_required(VERSION 3.24 FATAL_ERROR)
+
+project(dmf-node-fabric-bridge VERSION 0.1.0 LANGUAGES CXX)
+
+find_package(fmt CONFIG REQUIRED)
+find_package(spdlog CONFIG REQUIRED)
+find_package(nlohmann_json CONFIG REQUIRED)
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(libfabric REQUIRED IMPORTED_TARGET libfabric)
+
+add_executable(dmf-node-fabric-bridge
+    src/fabric_bridge_node.cpp
+    src/main.cpp
+)
+
+target_link_libraries(dmf-node-fabric-bridge PRIVATE
+    dmf-node
+    mxl-fabrics-objects
+    mxl-fabrics-headers
+    PkgConfig::libfabric
+    spdlog::spdlog
+    fmt::fmt
+    nlohmann_json::nlohmann_json
+)
+
+target_include_directories(dmf-node-fabric-bridge PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/src
+)

nodes/fabric-bridge/src/fabric_bridge_node.cpp

@@ -0,0 +1,320 @@
+#include "fabric_bridge_node.hpp"
+
+#include <mxl/mxl.h>
+
+#include <spdlog/spdlog.h>
+
+namespace dmf_node {
+
+FabricBridgeNode::~FabricBridgeNode() {
+    running_ = false;
+    if (worker_thread_.has_value() && worker_thread_->joinable()) {
+        worker_thread_->join();
+    }
+}
+
+std::vector<PortDef> FabricBridgeNode::input_ports() const {
+    if (mode_ == FabricMode::Target) {
+        return {};
+    }
+    return {{"video_in", PortDirection::Input, MediaType::VideoV210}};
+}
+
+std::vector<PortDef> FabricBridgeNode::output_ports() const {
+    if (mode_ == FabricMode::Initiator) {
+        return {};
+    }
+    return {{"video_out", PortDirection::Output, MediaType::VideoV210}};
+}
+
+void FabricBridgeNode::configure(const nlohmann::json& params) {
+    if (params.contains("mode")) {
+        auto mode_str = params["mode"].get<std::string>();
+        if (mode_str == "initiator") mode_ = FabricMode::Initiator;
+        else if (mode_str == "target") mode_ = FabricMode::Target;
+        else spdlog::warn("Fabric-bridge: unknown mode '{}', defaulting to initiator", mode_str);
+    }
+
+    if (params.contains("bind_node")) bind_node_ = params["bind_node"].get<std::string>();
+    if (params.contains("bind_service")) bind_service_ = params["bind_service"].get<std::string>();
+    if (params.contains("provider")) {
+        auto prov_str = params["provider"].get<std::string>();
+        mxlFabricsProviderFromString(prov_str.c_str(), &provider_);
+    }
+
+    if (params.contains("target_info")) {
+        target_info_str_ = params["target_info"].get<std::string>();
+    }
+}
+
+void FabricBridgeNode::on_add_writer(const std::string& port_id, mxlFlowWriter writer) {
+    if (port_id == "video_out") {
+        writer_ = writer;
+        spdlog::info("Fabric-bridge: writer added (target mode)");
+    }
+}
+
+void FabricBridgeNode::on_add_reader(const std::string& port_id, mxlFlowReader reader) {
+    if (port_id == "video_in") {
+        reader_ = reader;
+        spdlog::info("Fabric-bridge: reader added (initiator mode)");
+    }
+}
+
+void FabricBridgeNode::on_remove_writer(const std::string& port_id) {
+    if (port_id == "video_out") {
+        writer_.reset();
+        spdlog::info("Fabric-bridge: writer removed");
+    }
+}
+
+void FabricBridgeNode::on_remove_reader(const std::string& port_id) {
+    if (port_id == "video_in") {
+        reader_.reset();
+        spdlog::info("Fabric-bridge: reader removed");
+    }
+}
+
+void FabricBridgeNode::process() {
+    if (!worker_thread_.has_value()) {
+        if (mode_ == FabricMode::Initiator && reader_.has_value() && !target_info_str_.empty()) {
+            running_ = true;
+            worker_thread_ = std::thread(&FabricBridgeNode::run_initiator, this);
+        } else if (mode_ == FabricMode::Target && writer_.has_value()) {
+            running_ = true;
+            worker_thread_ = std::thread(&FabricBridgeNode::run_target, this);
+        }
+    }
+    std::this_thread::sleep_for(std::chrono::milliseconds(100));
+}
+
+void FabricBridgeNode::run_initiator() {
+    spdlog::info("Fabric-bridge: starting initiator mode");
+
+    auto instance = get_mxl_instance();
+    if (!instance) {
+        spdlog::error("Fabric-bridge: no MXL instance");
+        running_ = false;
+        return;
+    }
+
+    mxlFabricsInstance fab_inst = nullptr;
+    auto status = mxlFabricsCreateInstance(instance, nullptr, &fab_inst);
+    if (status != MXL_STATUS_OK || !fab_inst) {
+        spdlog::error("Fabric-bridge: failed to create fabrics instance: {}", static_cast<int>(status));
+        running_ = false;
+        return;
+    }
+    fabrics_instance_ = fab_inst;
+
+    mxlFabricsInitiator initiator = nullptr;
+    status = mxlFabricsCreateInitiator(fab_inst, &initiator);
+    if (status != MXL_STATUS_OK || !initiator) {
+        spdlog::error("Fabric-bridge: failed to create initiator: {}", static_cast<int>(status));
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+    initiator_ = initiator;
+
+    mxlFlowConfigInfo config{};
+    mxlFlowReaderGetConfigInfo(*reader_, &config);
+    grain_rate_ = config.common.grainRate;
+
+    mxlFabricsInitiatorConfig init_cfg{};
+    init_cfg.version = MXL_FABRICS_API_VERSION;
+    init_cfg.interface.version = MXL_FABRICS_API_VERSION;
+    init_cfg.interface.provider = provider_;
+    init_cfg.interface.address.node = bind_node_.c_str();
+    init_cfg.interface.address.service = bind_service_.c_str();
+    init_cfg.reader = *reader_;
+
+    status = mxlFabricsInitiatorSetup(initiator, &init_cfg, nullptr);
+    if (status != MXL_STATUS_OK) {
+        spdlog::error("Fabric-bridge: initiator setup failed: {}", static_cast<int>(status));
+        mxlFabricsDestroyInitiator(fab_inst, initiator);
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+
+    mxlFabricsTargetInfo target_info = nullptr;
+    status = mxlFabricsTargetInfoFromString(target_info_str_.c_str(), &target_info);
+    if (status != MXL_STATUS_OK || !target_info) {
+        spdlog::error("Fabric-bridge: failed to parse target_info: {}", static_cast<int>(status));
+        mxlFabricsDestroyInitiator(fab_inst, initiator);
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+
+    status = mxlFabricsInitiatorAddTarget(initiator, target_info);
+    if (status != MXL_STATUS_OK) {
+        spdlog::error("Fabric-bridge: failed to add target: {}", static_cast<int>(status));
+        mxlFabricsFreeTargetInfo(target_info);
+        mxlFabricsDestroyInitiator(fab_inst, initiator);
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+
+    spdlog::info("Fabric-bridge: waiting for connection...");
+    do {
+        status = mxlFabricsInitiatorMakeProgressBlocking(initiator, 250);
+    } while (status == MXL_ERR_NOT_READY && running_);
+    spdlog::info("Fabric-bridge: connected");
+
+    auto now = mxlGetTime();
+    read_index_ = mxlTimestampToIndex(&grain_rate_, now) - 2;
+
+    spdlog::info("Fabric-bridge: initiator started, grain_rate={}/{}", grain_rate_.numerator, grain_rate_.denominator);
+
+    while (running_) {
+        auto deadline = mxlIndexToTimestamp(&grain_rate_, read_index_ + 1);
+        mxlSleepUntil(deadline);
+
+        mxlGrainInfo grain_info{};
+        uint8_t* payload = nullptr;
+        auto grain_status = mxlFlowReaderGetGrain(*reader_, read_index_, 5000000ULL, &grain_info, &payload);
+        if (grain_status != MXL_STATUS_OK) {
+            if (grain_status == MXL_ERR_OUT_OF_RANGE_TOO_LATE || grain_status == MXL_ERR_OUT_OF_RANGE_TOO_EARLY) {
+                auto ts = mxlGetTime();
+                read_index_ = mxlTimestampToIndex(&grain_rate_, ts) - 2;
+                continue;
+            }
+            read_index_++;
+            continue;
+        }
+
+        auto transfer_status = mxlFabricsInitiatorTransferGrain(initiator, read_index_, 0, grain_info.validSlices);
+        if (transfer_status != MXL_STATUS_OK) {
+            spdlog::warn("Fabric-bridge: transfer grain {} failed: {}", read_index_, static_cast<int>(transfer_status));
+            read_index_++;
+            continue;
+        }
+
+        do {
+            status = mxlFabricsInitiatorMakeProgressBlocking(initiator, 10);
+        } while (status == MXL_ERR_NOT_READY && running_);
+
+        read_index_++;
+        grains_transferred_++;
+
+        if (grains_transferred_ == 1) {
+            spdlog::info("Fabric-bridge: first grain transferred, index={}", read_index_ - 1);
+        }
+    }
+
+    mxlFabricsInitiatorRemoveTarget(initiator, target_info);
+    mxlFabricsFreeTargetInfo(target_info);
+    mxlFabricsDestroyInitiator(fab_inst, initiator);
+    mxlFabricsDestroyInstance(fab_inst);
+    spdlog::info("Fabric-bridge: initiator stopped");
+}
+
+void FabricBridgeNode::run_target() {
+    spdlog::info("Fabric-bridge: starting target mode");
+
+    auto instance = get_mxl_instance();
+    if (!instance) {
+        spdlog::error("Fabric-bridge: no MXL instance");
+        running_ = false;
+        return;
+    }
+
+    mxlFabricsInstance fab_inst = nullptr;
+    auto status = mxlFabricsCreateInstance(instance, nullptr, &fab_inst);
+    if (status != MXL_STATUS_OK || !fab_inst) {
+        spdlog::error("Fabric-bridge: failed to create fabrics instance: {}", static_cast<int>(status));
+        running_ = false;
+        return;
+    }
+    fabrics_instance_ = fab_inst;
+
+    mxlFabricsTarget tgt = nullptr;
+    status = mxlFabricsCreateTarget(fab_inst, &tgt);
+    if (status != MXL_STATUS_OK || !tgt) {
+        spdlog::error("Fabric-bridge: failed to create target: {}", static_cast<int>(status));
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+    target_ = tgt;
+
+    mxlFlowConfigInfo config{};
+    mxlFlowWriterGetConfigInfo(*writer_, &config);
+    grain_rate_ = config.common.grainRate;
+
+    mxlFabricsTargetConfig target_cfg{};
+    target_cfg.version = MXL_FABRICS_API_VERSION;
+    target_cfg.interface.version = MXL_FABRICS_API_VERSION;
+    target_cfg.interface.provider = provider_;
+    target_cfg.interface.address.node = bind_node_.c_str();
+    target_cfg.interface.address.service = bind_service_.c_str();
+    target_cfg.writer = *writer_;
+
+    mxlFabricsTargetInfo target_info = nullptr;
+    status = mxlFabricsTargetSetup(tgt, &target_cfg, nullptr, &target_info);
+    if (status != MXL_STATUS_OK || !target_info) {
+        spdlog::error("Fabric-bridge: target setup failed: {}", static_cast<int>(status));
+        mxlFabricsDestroyTarget(fab_inst, tgt);
+        mxlFabricsDestroyInstance(fab_inst);
+        running_ = false;
+        return;
+    }
+
+    size_t info_size = 0;
+    mxlFabricsTargetInfoToString(target_info, nullptr, &info_size);
+    std::vector<char> info_buf(info_size);
+    mxlFabricsTargetInfoToString(target_info, info_buf.data(), &info_size);
+    target_info_str_ = std::string(info_buf.data(), info_size);
+
+    spdlog::info("Fabric-bridge: target ready, target_info length={}", target_info_str_.size());
+    spdlog::info("Fabric-bridge: TARGET_INFO={}", target_info_str_);
+
+    while (running_) {
+        uint64_t grain_index = 0;
+        status = mxlFabricsTargetReadGrain(tgt, 200, &grain_index);
+        if (status == MXL_ERR_TIMEOUT || status == MXL_ERR_NOT_READY) {
+            continue;
+        }
+        if (status != MXL_STATUS_OK) {
+            spdlog::warn("Fabric-bridge: target read grain failed: {}", static_cast<int>(status));
+            continue;
+        }
+
+        mxlGrainInfo grain_info{};
+        uint8_t* dummy_payload = nullptr;
+        auto open_status = mxlFlowWriterOpenGrain(*writer_, grain_index, &grain_info, &dummy_payload);
+        if (open_status == MXL_STATUS_OK) {
+            grain_info.validSlices = grain_info.totalSlices;
+            mxlFlowWriterCommitGrain(*writer_, &grain_info);
+            grains_transferred_++;
+            if (grains_transferred_ == 1) {
+                spdlog::info("Fabric-bridge: first grain committed, index={}", grain_index);
+            }
+        } else {
+            spdlog::warn("Fabric-bridge: open grain {} failed: {}", grain_index, static_cast<int>(open_status));
+        }
+    }
+
+    mxlFabricsFreeTargetInfo(target_info);
+    mxlFabricsDestroyTarget(fab_inst, tgt);
+    mxlFabricsDestroyInstance(fab_inst);
+    spdlog::info("Fabric-bridge: target stopped");
+}
+
+nlohmann::json FabricBridgeNode::status() const {
+    return {
+        {"type", "fabric-bridge"},
+        {"mode", mode_ == FabricMode::Initiator ? "initiator" : "target"},
+        {"grains_transferred", grains_transferred_},
+        {"running", running_.load()},
+        {"has_reader", reader_.has_value()},
+        {"has_writer", writer_.has_value()},
+        {"target_info_length", target_info_str_.size()},
+        {"target_info", target_info_str_},
+    };
+}
+
+} // namespace dmf_node

nodes/fabric-bridge/src/fabric_bridge_node.hpp

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <dmf-node/node.hpp>
+#include <mxl/flow.h>
+#include <mxl/fabrics.h>
+#include <mxl/time.h>
+
+#include <atomic>
+#include <optional>
+#include <string>
+#include <thread>
+
+namespace dmf_node {
+
+enum class FabricMode { Initiator, Target };
+
+class FabricBridgeNode : public Node {
+public:
+    FabricBridgeNode() = default;
+    ~FabricBridgeNode();
+
+    std::string type() const override { return "fabric-bridge"; }
+
+    std::vector<PortDef> input_ports() const override;
+    std::vector<PortDef> output_ports() const override;
+
+    void configure(const nlohmann::json& params) override;
+    void on_add_writer(const std::string& port_id, mxlFlowWriter writer) override;
+    void on_add_reader(const std::string& port_id, mxlFlowReader reader) override;
+    void on_remove_writer(const std::string& port_id) override;
+    void on_remove_reader(const std::string& port_id) override;
+
+    void process() override;
+    nlohmann::json status() const override;
+
+private:
+    void run_initiator();
+    void run_target();
+
+    FabricMode mode_ = FabricMode::Initiator;
+
+    std::string bind_node_ = "0.0.0.0";
+    std::string bind_service_ = "0";
+    mxlFabricsProvider provider_ = MXL_FABRICS_PROVIDER_ANY;
+
+    std::optional<mxlFlowReader> reader_;
+    std::optional<mxlFlowWriter> writer_;
+    mxlRational grain_rate_{50, 1};
+    uint64_t read_index_ = 0;
+    uint64_t grains_transferred_ = 0;
+
+    std::string target_info_str_;
+
+    mxlFabricsInstance fabrics_instance_ = nullptr;
+    mxlFabricsInitiator initiator_ = nullptr;
+    mxlFabricsTarget target_ = nullptr;
+
+    std::optional<std::thread> worker_thread_;
+    std::atomic<bool> running_{false};
+};
+
+} // namespace dmf_node

nodes/fabric-bridge/src/main.cpp

@@ -0,0 +1,11 @@
+#include "fabric_bridge_node.hpp"
+#include <dmf-node/node_runner.hpp>
+
+int main(int argc, char* argv[]) {
+    dmf_node::NodeRunner runner;
+    if (!runner.parse_args(argc, argv)) {
+        return 1;
+    }
+    auto node = std::make_unique<dmf_node::FabricBridgeNode>();
+    return runner.exec(std::move(node));
+}