本指南說明如何使用 metadata 程式庫。中繼資料可以是任意資料 由驅動程式庫在繫結至節點時建立,應可存取 繫結至其子節點的驅動程式在一般情況下,駕駛可以自行建立 FIDL 通訊協定傳輸中繼資料,但 metadata 程式庫提供傳遞憑證的功能 將中繼資料提供給駕駛人,使用更少的程式碼
您可以參考的例子,瞭解為何駕駛人傳送、擷取及轉送中繼資料 請按這裡。
中繼資料定義
首先,中繼資料類型必須定義為 FIDL 類型:
library fuchsia.examples.metadata;
// Type of the metadata to be passed.
type Metadata = table {
1: test_property string:MAX;
};
這項中繼資料將使用
fuchsia.driver.metadata/Service
FIDL 服務。不過,外送命名空間中的 Service 名稱
並非 fuchsia.driver.metadata.Service
。而是自訂的
我們提供的字串,與中繼資料的類型有關。
在本教學課程中,我們將在同一個 FIDL 程式庫中定義該字串,如上所示:
library fuchsia.examples.metadata;
const SERVICE string = "fuchsia.examples.metadata.Metadata";
FIDL 程式庫的建構目標將定義如下:
fidl("fuchsia.examples.metadata") {
sources = [ "fuchsia.examples.metadata.fidl" ]
}
中繼資料庫
如要使用 metadata 程式庫,我們需要將 fdf_metadata::ObjectDetails 範本 類別如下:
#include <fidl/fuchsia.examples.metadata/cpp/fidl.h>
// `ObjectDetails` must be specialized within the `fdf_metadata` namespace.
namespace fdf_metadata {
template <>
// Pass the metadata type as the template argument.
struct ObjectDetails<fuchsia_examples_metadata::Metadata> {
// Specify the name of the service used to serve the metadata.
inline static const char* Name = fuchsia_examples_metadata::kService;
};
} // namespace fdf_metadata
由於貨運業者和接收者都必須進行這項設定,因此我們可將 複製到新程式庫中,由這兩個驅動程式一同包含:
source_set("examples_metadata") {
# This header file should contain the above code.
sources = [ "examples_metadata.h" ]
public_deps = [
# This should be the fuchsia.examples.metadata FIDL library's C++ target.
":fuchsia.examples.metadata_cpp",
]
}
正在傳送中繼資料
初始設定
假設有一個驅動程式庫想將中繼資料傳送給其子項:
#include <lib/driver/component/cpp/driver_export.h>
class Sender : public fdf::DriverBase {
public:
Sender(fdf::DriverStartArgs start_args, fdf::UnownedSynchronizedDispatcher driver_dispatcher)
: DriverBase("parent", std::move(start_args), std::move(driver_dispatcher)) {}
};
FUCHSIA_DRIVER_EXPORT(Sender);
元件資訊清單如下: ``` { 包含:[ "inspect/client.shard.cml", "syslog/client.shard.cml", ], program: { 執行元件: "驅動程式庫", 二進位檔案:「driver/parent.so」、 繫結: "meta/繫結/parent.bindbc", },您好: }
It's build targets are defined as follows:
fuchsia_driver("driver") { testonly = true output_name =「parent」 source = [ "parent.cc", ] deps = [ "//src/devices/lib/driver:driver_runtime", ] }
fuchsia_driver_component("component") { testonly = true 元件名稱 = 「父項」 資訊清單 =「meta/parent.cml」 deps = [ ":driver", ":bind", # 個未在本教學課程中指定的繫結規則。 ] info =「parent.json」# 本教學課程未指定資訊。 } ```
傳送程序
此驅動程式庫必須具有
執行個體
fdf_metadata::MetadataServer
類別的呼叫,呼叫
fdf_metadata::MetadataServer::SetMetadata()
方法,然後提供
將中繼資料傳送至驅動程式庫傳出目錄,方法是呼叫
fdf_metadata::MetadataServer::Serve()
方法:
// Make sure to include the metadata library that specializes the
// `fdf_metadata::ObjectDetails` class. It is needed by
// `fdf_metadata::MetadataServer`.
#include "examples_metadata.h"
#include <lib/driver/metadata/cpp/metadata_server.h>
class Sender : public fdf::DriverBase {
public:
zx::result<> Start() override {
// Set the metadata to be served.
fuchsia_examples_metadata::Metadata metadata{{.test_property = "test value"}};
ZX_ASSERT(metadata_server_.SetMetadata(std::move(metadata)) == ZX_OK);
// Serve the metadata to the driver's outgoing directory.
ZX_ASSERT(metadata_server_.Serve(*outgoing(), dispatcher()) == ZX_OK);
return zx::ok();
}
private:
// Responsible for serving metadata.
fdf_metadata::MetadataServer<fuchsia_examples_metadata::Metadata> metadata_server_;
};
fdf_metadata::MetadataServer::SetMetadata()
可以多次呼叫
在 fdf_metadata::MetadataServer::Serve()
之前或之後,以及中繼資料伺服器
將提供最新的中繼資料執行個體驅動程式將無法擷取
未呼叫 fdf_metadata::MetadataServer::SetMetadata()
時的中繼資料
然後嘗試擷取中繼資料
需要更新 driver
建構目標:
fuchsia_driver("driver") {
testonly = true
output_name = "parent"
sources = [
"parent.cc",
]
deps = [
"//src/devices/lib/driver:driver_runtime",
":examples_metadata",
]
}
公開中繼資料服務
最後,驅動程式庫需要宣告
fuchsia.examples.metadata.Metadata
FIDL 服務位於元件資訊清單中:
{
include: [
"inspect/client.shard.cml",
"syslog/client.shard.cml",
],
program: {
runner: "driver",
binary: "driver/parent.so",
bind: "meta/bind/parent.bindbc",
},
capabilities: [
{ service: "fuchsia.examples.metadata.Metadata" },
],
expose: [
{
service: "fuchsia.examples.metadata.Metadata",
from: "self",
},
],
}
就技術層面而言,我們不提供 fuchsia.examples.metadata.Metadata
FIDL 服務。
但其實
fdf_metadata::MetadataServer
會放送
fuchsia.driver.metadata/Service
FIDL 服務,以便傳送中繼資料。不過
fdf_metadata::MetadataServer
並未以「fuchsia.driver.metadata.Service
」這個名稱提供這項服務
視為一般 FIDL 服務而是以「名稱」之下提供服務
fuchsia.examples.metadata.Metadata
。讓接收端驅動程式庫
識別傳遞的中繼資料類型這表示我們必須宣告
並公開 fuchsia.examples.metadata.Metadata
服務
服務不存在
擷取中繼資料
初始設定
假設有一個驅動程式庫想接收來自父項的中繼資料 驅動程式庫:
#include <lib/driver/component/cpp/driver_export.h>
class Retriever : public fdf::DriverBase {
public:
Retriever(fdf::DriverStartArgs start_args, fdf::UnownedSynchronizedDispatcher driver_dispatcher)
: DriverBase("child", std::move(start_args), std::move(driver_dispatcher)) {}
};
FUCHSIA_DRIVER_EXPORT(Retriever);
元件資訊清單如下:
{
include: [
"inspect/client.shard.cml",
"syslog/client.shard.cml",
],
program: {
runner: "driver",
binary: "driver/child.so",
bind: "meta/bind/child.bindbc",
},
}
其建構目標的定義如下:
fuchsia_driver("driver") {
testonly = true
output_name = "child"
sources = [
"child.cc",
]
deps = [
"//src/devices/lib/driver:driver_runtime",
]
}
fuchsia_driver_component("component") {
testonly = true
component_name = "child"
manifest = "meta/child.cml"
deps = [
":driver",
":bind", # Bind rules not specified in this tutorial.
]
info = "child.json" # Info not specified in this tutorial.
}
擷取程序
為了從驅動程式庫的驅動程式庫上擷取中繼資料,驅動程式庫會
呼叫 fdf_metadata::GetMetadata()
:
#include <lib/driver/metadata/cpp/metadata.h>
// Make sure to include the metadata library that specializes the
// `fdf_metadata::ObjectDetails` class. It is needed by
// `fdf_metadata::GetMetadata()`.
#include "examples_metadata.h"
class Retriever : public fdf::DriverBase {
public:
zx::result<> Start() override {
zx::result<fuchsia_examples_metadata::Metadata> metadata =
fdf_metadata::GetMetadata<fuchsia_examples_metadata::Metadata>(incoming());
ZX_ASSERT(!metadata.is_error());
return zx::ok();
}
};
需要更新 driver
建構目標:
fuchsia_driver("driver") {
testonly = true
output_name = "child"
sources = [
"child.cc",
]
deps = [
"//src/devices/lib/driver:driver_runtime",
":examples_metadata",
]
}
使用中繼資料服務
最後,驅動程式庫需要宣告其使用
fuchsia.examples.metadata.Metadata
FIDL 服務位於元件資訊清單中:
{
include: [
"inspect/client.shard.cml",
"syslog/client.shard.cml",
],
program: {
runner: "driver",
binary: "driver/child.so",
bind: "meta/bind/child.bindbc",
},
use: [
{ service: "fuchsia.examples.metadata.Metadata" },
],
}
轉送中繼資料
初始設定
假設某個驅動程式庫想從父項擷取中繼資料 然後再將此中繼資料轉送至其子項驅動程式:
#include <lib/driver/component/cpp/driver_export.h>
class Forwarder : public fdf::DriverBase {
public:
Forwarder(fdf::DriverStartArgs start_args, fdf::UnownedSynchronizedDispatcher driver_dispatcher)
: DriverBase("forward", std::move(start_args), std::move(driver_dispatcher)) {}
};
FUCHSIA_DRIVER_EXPORT(Forwarder);
元件資訊清單如下:
{
include: [
"inspect/client.shard.cml",
"syslog/client.shard.cml",
],
program: {
runner: "driver",
binary: "driver/forward_driver.so",
bind: "meta/bind/forward.bindbc",
},
}
其建構目標的定義如下:
fuchsia_driver("driver") {
testonly = true
output_name = "forward_driver"
sources = [
"forward_driver.cc",
]
deps = [
"//src/devices/lib/driver:driver_runtime",
]
}
fuchsia_driver_component("component") {
testonly = true
component_name = "forward"
manifest = "meta/forward.cml"
deps = [
":driver",
":bind", # Bind rules not specified in this tutorial.
]
info = "forward.json" # Info not specified in this tutorial.
}
轉送程序
讓驅動程式庫將中繼資料從父項驅動程式庫轉送至其子項
就必須建立
fdf_metadata::MetadataServer
類別的呼叫,呼叫
fdf_metadata::MetadataServer::ForwardMetadata()
方法,然後提供
將中繼資料傳送至驅動程式庫傳出目錄,方法是呼叫
fdf_metadata::MetadataServer::Serve()
方法:
// Make sure to include the metadata library that specializes the
// `fdf_metadata::ObjectDetails` class. It is needed by
// `fdf_metadata::MetadataServer`.
#include "examples_metadata.h"
#include <lib/driver/metadata/cpp/metadata_server.h>
class Forwarder : public fdf::DriverBase {
public:
zx::result<> Start() override {
// Set metadata using the driver's parent driver metadata.
ZX_ASSERT(metadata_server_.ForwardMetadata(incoming()) == ZX_OK);
// Serve the metadata to the driver's outgoing directory.
ZX_ASSERT(metadata_server_.Serve(*outgoing(), dispatcher()) == ZX_OK);
return zx::ok();
}
private:
// Responsible for serving metadata.
fdf_metadata::MetadataServer<fuchsia_examples_metadata::Metadata> metadata_server_;
};
請注意,fdf_metadata::MetadataServer::ForwardMetadata()
會
未確認家長驅動程式庫是否變更了先前提供的中繼資料
已呼叫 fdf_metadata::MetadataServer::ForwardMetadata()
。駕駛人
將在以下時間過後再次呼叫 fdf_metadata::MetadataServer::ForwardMetadata()
:
以便導入變更
需要更新 driver
建構目標:
fuchsia_driver("driver") {
testonly = true
output_name = "forward_driver"
sources = [
"forward_driver.cc",
]
deps = [
"//src/devices/lib/driver:driver_runtime",
":examples_metadata",
]
}
公開及使用中繼資料服務
最後,驅動程式庫需要宣告、使用及公開
fuchsia.examples.metadata.Metadata
FIDL 服務位於元件資訊清單中:
{
include: [
"inspect/client.shard.cml",
"syslog/client.shard.cml",
],
program: {
runner: "driver",
binary: "driver/forward_driver.so",
bind: "meta/bind/forward.bindbc",
},
capabilities: [
{ service: "fuchsia.examples.metadata.Metadata" },
],
expose: [
{
service: "fuchsia.examples.metadata.Metadata",
from: "self",
},
],
use: [
{ service: "fuchsia.examples.metadata.Metadata" },
],
}