本頁面由 Cloud Translation API 翻譯而成。

公開駕駛功能

驅動程式元件可提供為其他駕駛人提供的功能和服務非驅動程式庫元件的功能。如此一來， Fuchsia 的元件架構就能將這些能力轉化為以及目標元件駕駛也可以將自身能力匯出至 devfs，讓其他元件能夠以檔案形式加以探索元件的命名空間

在本節中，您將公開 qemu_edu 驅動程式庫的階乘功能從系統其他位置執行的元件取用

建立新的 FIDL 程式庫

在 Bazel 工作區中，為新的 FIDL 程式庫建立新的專案目錄：

mkdir -p fuchsia-codelab/qemu_edu/fidl

完成這個部分後，專案應具備下列目錄：結構：

//fuchsia-codelab/qemu_edu/fidl
                  |- BUILD.bazel
                  |- qemu_edu.fidl

建立 qemu_edu/fidl/BUILD.bazel 檔案，並將下列陳述式新增至包含 Fuchsia SDK 的必要建構規則：

qemu_edu/fidl/BUILD.bazel：

load(
    "@fuchsia_sdk//fuchsia:defs.bzl",
    "fuchsia_fidl_library",
    "fuchsia_fidl_llcpp_library",
)

定義驅動程式庫服務通訊協定

驅動程式會使用自訂 FIDL 公開 edu 裝置的功能因此效能相當卓越使用以下指令將新的「qemu_edu/qemu_edu.fidl」檔案新增至專案工作區：包含下列內容：

qemu_edu/fidl/qemu_edu.fidl：

library examples.qemuedu;

using zx;

/// The Device protocol provides access to the functions of the QEMU edu hardware.
@discoverable
open protocol Device {
    /// Computes the factorial of 'input' using the edu device and returns the
    /// result.
    flexible ComputeFactorial(struct {
        input uint32;
    }) -> (struct {
        output uint32;
    }) error zx.Status;

    /// Performs a liveness check and return true if the device passes.
    flexible LivenessCheck() -> (struct {
        result bool;
    }) error zx.Status;
};

/// The Service enables the driver framework to offer the Device protocol to
/// other components.
service Service {
    device client_end:Device;
};

此 FIDL 通訊協定提供兩種與階乘互動的方法運算和有效性檢查硬體註冊都會在 edu 裝置上註冊。

將下列建構規則新增至專案的建構設定底部編譯 FIDL 程式庫並產生 C++ 繫結：

fuchsia_fidl_library()：宣告 examples.qemuedu FIDL ，並描述其包含的 FIDL 來源檔案。
fuchsia_fidl_llcpp_library()：說明產生的給元件的 C++ 連接線與此 FIDL 程式庫互動

qemu_edu/fidl/BUILD.bazel：

fuchsia_fidl_library(
    name = "examples.qemuedu",
    srcs = [
        "qemu_edu.fidl",
    ],
    library = "examples.qemuedu",
    visibility = ["//visibility:public"],
    deps = [
        "@fuchsia_sdk//fidl/zx",
    ],
)

fuchsia_fidl_llcpp_library(
    name = "examples.qemuedu_cc",
    library = ":examples.qemuedu",
    visibility = ["//visibility:public"],
    deps = [
        "@fuchsia_sdk//fidl/zx:zx_llcpp_cc",
        "@fuchsia_sdk//pkg/fidl_cpp_wire",
    ],
)

實作驅動程式庫服務通訊協定

定義 FIDL 通訊協定後，您需要更新驅動程式庫才能導入並將這個通訊協定提供給其他元件

完成這個部分後，專案應具備下列目錄：結構：

//fuchsia-codelab/qemu_edu/drivers
                  |- BUILD.bazel
                  |- meta
                  |   |- qemu_edu.cml
                  |- edu_device.cc
                  |- edu_device.h
                  |- edu_server.cc 
                  |- edu_server.h 
                  |- qemu_edu.bind
                  |- qemu_edu.cc
                  |- qemu_edu.h

在專案目錄中建立新的 qemu_edu/drivers/edu_server.h 檔案並在當中加入下列內容： examples.qemuedu 程式庫並建立新的 QemuEduServer 類別，實作 FIDL 通訊協定的伺服器端：

qemu_edu/drivers/edu_server.h：

#ifndef FUCHSIA_CODELAB_QEMU_EDU_SERVER_H_
#define FUCHSIA_CODELAB_QEMU_EDU_SERVER_H_

#include <fidl/examples.qemuedu/cpp/wire.h>
#include <lib/driver/logging/cpp/structured_logger.h>

#include "edu_device.h"

namespace qemu_edu {

// FIDL server implementation for the `examples.qemuedu/Device` protocol.
class QemuEduServer : public fidl::WireServer<examples_qemuedu::Device> {
 public:
  explicit QemuEduServer(std::weak_ptr<edu_device::QemuEduDevice> device)
      : device_(std::move(device)) {}

  static fidl::ServerBindingRef<examples_qemuedu::Device> BindDeviceClient(
      async_dispatcher_t* dispatcher, std::weak_ptr<edu_device::QemuEduDevice> device,
      fidl::ServerEnd<examples_qemuedu::Device> request) {
    // Bind each connection request to a unique FIDL server instance
    auto server_impl = std::make_unique<QemuEduServer>(device);
    return fidl::BindServer(dispatcher, std::move(request), std::move(server_impl),
                            std::mem_fn(&QemuEduServer::OnUnbound));
  }

  // This method is called when a server connection is torn down.
  void OnUnbound(fidl::UnbindInfo info, fidl::ServerEnd<examples_qemuedu::Device> server_end) {
    if (info.is_peer_closed()) {
      FDF_LOG(DEBUG, "Client disconnected");
    } else if (!info.is_user_initiated()) {
      FDF_LOG(ERROR, "Client connection unbound: %s", info.status_string());
    }
  }

  // fidl::WireServer<examples_qemuedu::Device>

  void ComputeFactorial(ComputeFactorialRequestView request,
                        ComputeFactorialCompleter::Sync& completer) override;
  void LivenessCheck(LivenessCheckCompleter::Sync& completer) override;
  void handle_unknown_method(fidl::UnknownMethodMetadata<examples_qemuedu::Device> metadata,
                             fidl::UnknownMethodCompleter::Sync& completer) override;

 private:
  std::weak_ptr<edu_device::QemuEduDevice> device_;
};

}  // namespace qemu_edu

#endif  // FUCHSIA_CODELAB_QEMU_EDU_SERVER_H_

在專案目錄中建立新的 qemu_edu/drivers/edu_server.cc 檔案包含下列內容來實作 examples.qemuedu/Device 並對應至裝置資源方法：

qemu_edu/drivers/edu_server.cc：

#include "edu_server.h"

namespace qemu_edu {

// Driver Service: Compute factorial on the edu device
void QemuEduServer::ComputeFactorial(ComputeFactorialRequestView request,
                                     ComputeFactorialCompleter::Sync& completer) {
  auto edu_device = device_.lock();
  if (!edu_device) {
    FDF_LOG(ERROR, "Unable to access device resources.");
    completer.ReplyError(ZX_ERR_BAD_STATE);
    return;
  }

  uint32_t input = request->input;

  edu_device->ComputeFactorial(
      input, [completer = completer.ToAsync()](zx::result<uint32_t> result_status) mutable {
        if (result_status.is_error()) {
          completer.ReplyError(result_status.error_value());
          return;
        }
        uint32_t factorial = result_status.value();
        completer.ReplySuccess(factorial);
      });
}

// Driver Service: Complete a liveness check on the edu device
void QemuEduServer::LivenessCheck(LivenessCheckCompleter::Sync& completer) {
  auto edu_device = device_.lock();
  if (!edu_device) {
    FDF_LOG(ERROR, "Unable to access device resources.");
    completer.ReplyError(ZX_ERR_BAD_STATE);
    return;
  }

  constexpr uint32_t kChallenge = 0xdeadbeef;
  constexpr uint32_t kExpectedResponse = ~(kChallenge);

  auto status = edu_device->LivenessCheck(kChallenge);
  if (status.is_error()) {
    FDF_LOG(ERROR, "Unable to send liveness check request.");
    completer.ReplyError(status.error_value());
    return;
  }
  const bool alive = (status.value() == kExpectedResponse);

  FDF_SLOG(INFO, "Replying with", KV("result", alive));
  completer.ReplySuccess(alive);
}

}  // namespace qemu_edu

更新驅動程式庫的元件資訊清單，以宣告並公開 FIDL 通訊協定一項能力

qemu_edu/drivers/meta/qemu_edu.cml：

{
    include: [
        "syslog/client.shard.cml",
    ],
    program: {
        runner: 'driver',
        binary: 'driver/libqemu_edu.so',
        bind: 'meta/bind/qemu_edu.bindbc',
        // Identifies the device categories, for compatibility tests. This
        // example driver uses the 'misc' category; real drivers should
        // select a more specific category.
        device_categories: [
          { category: 'misc', subcategory: '' },
        ],
    },
    use: [
        { service: 'fuchsia.hardware.pci.Service' },
    ],
    // Provide the device capability to other components
    capabilities: [
        { service: 'examples.qemuedu.Service' },
    ],
    expose: [
        {
            service: 'examples.qemuedu.Service',
            from: 'self',
        },
    ],
}

更新驅動程式庫的建構設定，以依附於新的 examples.qemuedu 程式庫：

qemu_edu/drivers/BUILD.bazel：

fuchsia_cc_driver(
    name = "qemu_edu",
    srcs = [
        "edu_device.cc",
        "edu_device.h",
        "edu_server.cc",
        "edu_server.h",
        "qemu_edu.cc",
        "qemu_edu.h",
    ],
    deps = [
        "//fuchsia-codelab/qemu_edu/fidl:examples.qemuedu_cc",
        "@fuchsia_sdk//fidl/fuchsia.hardware.pci:fuchsia.hardware.pci_llcpp_cc",
        "@fuchsia_sdk//pkg/driver_component_cpp",
        "@fuchsia_sdk//pkg/driver_devfs_cpp",
        "@fuchsia_sdk//pkg/hwreg",
        "@fuchsia_sdk//pkg/mmio",
    ],
)

匯出及提供通訊協定

qemu_edu 驅動程式庫會使 examples.qemuedu/Device 通訊協定成為可透過 devfs 找到其他元件用於找出哪些驅動程式庫服務可以使用非驅動程式庫元件查詢裝置檔案系統 (通常掛接到元件命名空間中的 /dev)，然後掃描檔案系統下的目錄和檔案

驅動程式管理員可將 devfs 中的項目別名為特定裝置類別項目 (例如 /dev/class/input) 會將通訊協定 ID 與已知提供的裝置類別如果非驅動程式庫元件不知道確切路徑是特定類型，而非特定類型在本練習中，edu 裝置不符合已知的類別，因此您將將這個項目設為未分類裝置。

更新驅動程式庫元件的資訊清單，以要求 fuchsia.devics.fs.Exporter 能力：

qemu_edu/drivers/meta/qemu_edu.cml：

{
    include: [
        "syslog/client.shard.cml",
    ],
    program: {
        runner: 'driver',
        binary: 'driver/libqemu_edu.so',
        bind: 'meta/bind/qemu_edu.bindbc',
        // Identifies the device categories, for compatibility tests. This
        // example driver uses the 'misc' category; real drivers should
        // select a more specific category.
        device_categories: [
          { category: 'misc', subcategory: '' },
        ],
    },
    use: [
        { service: 'fuchsia.hardware.pci.Service' },
    ],
    // Provide the device capability to other components
    capabilities: [
        { service: 'examples.qemuedu.Service' },
    ],
    expose: [
        {
            service: 'examples.qemuedu.Service',
            from: 'self',
        },
    ],
}

更新驅動程式庫的 Start() 方法，開始提供 examples.qemuedu/Device 通訊協定複製到符合裝置節點拓撲路徑的新 devfs 項目：

qemu_edu/drivers/qemu_edu.cc：

#include "qemu_edu.h"

#include <lib/driver/component/cpp/driver_export.h>

#include "edu_server.h"

// Initialize this driver instance
zx::result<> QemuEduDriver::Start() {
  // ...

  // Report the version information from the edu device.
  auto version_reg = device_->IdentificationRegister();
  FDF_SLOG(INFO, "edu device version", KV("major", version_reg.major_version()),
           KV("minor", version_reg.minor_version()));

  // Serve the examples.qemuedu/Service capability.
  examples_qemuedu::Service::InstanceHandler handler({
      .device = fit::bind_member<&QemuEduDriver::Serve>(this),
  });

  auto add_result = outgoing()->AddService<examples_qemuedu::Service>(std::move(handler));
  if (add_result.is_error()) {
    FDF_SLOG(ERROR, "Failed to add Device service", KV("status", add_result.status_string()));
    return add_result.take_error();
  }

  if (zx::result result = ExportToDevfs(); result.is_error()) {
    FDF_SLOG(ERROR, "Failed to export to devfs", KV("status", result.status_string()));
    return result.take_error();
  }
  // Create and export a devfs entry for the driver service.

  return zx::ok();
}

其他元件現在可找到 qemu_edu 驅動程式庫的功能。

重建驅動程式庫

使用 bazel build 指令驗證驅動程式庫是否成功建構：程式碼變更：

bazel build //fuchsia-codelab/qemu_edu/drivers:pkg

恭喜！您已成功從 Fuchsia 驅動程式公開 FIDL 服務。

設定硬體資源

與駕駛人互動