1.说明

本节介绍如何使用sdbusplus，用来对应不同的场景。

可以参考之前的文章: https://blog.csdn.net/wit_yuan/article/details/145192471

建议阅读本篇文章一定要仔细阅读sd-bus specification

2.说明

2.1 简单server服务注册

本节参考: https://gitee.com/wit_yuan/openbmc_testcode/blob/yuan_test_sdbusplus_1/recipe-example/files/test_add_interface.cpp
简单的注册服务，可以只需要使用几个api即可,基本代码如下:

#include <xyz/openbmc_project/net/Calculator/client.hpp>
#include <xyz/openbmc_project/net/Calculator/server.hpp>
#include <sdbusplus/server.hpp>

#include <iostream>
#include <string_view>

#include <sdbusplus/asio/connection.hpp>
#include <sdbusplus/asio/object_server.hpp>
#include <sdbusplus/asio/property.hpp>

#include <sys/sysinfo.h>
#include <systemd/sd-journal.h>

static std::string busServiceName = "xyz.openbmc_project.test.MyTestService";
int main()
{
    std::shared_ptr<sdbusplus::asio::connection> conn;
    boost::asio::io_context io;
    conn = std::make_shared<sdbusplus::asio::connection>(io);
    conn->request_name(busServiceName.c_str());
    io.run();
    return 0;
}

简单说一下调用实际的功能:

std::make_shared<sdbusplus::asio::connection>(io)

在文件build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/asio/connection.hpp中有定义:

    connection(boost::asio::io_context& io) :
        sdbusplus::bus_t(sdbusplus::bus::new_default()), io_(io),
        socket(io_.get_executor(), get_fd())
    {
        read_immediate();
    }

因此，默认其实调用了函数:

sdbusplus::bus::new_default()

另外:sdbusplus::bus_t(sdbusplus::bus::new_default())实际调用了文件:build/evb-ast2500/workspace/sources/sdbusplus/src/bus.cpp中的函数内容:

bus::bus(busp_t b) :
    _intf(&sdbus_impl),
    _bus(_intf->sd_bus_ref(b), details::BusDeleter(&sdbus_impl))
{
    // Emitting object added causes a message to get the properties
    // which can trigger a 'transaction' in the server bindings.  If
    // the bus isn't up far enough, this causes an assert deep in
    // sd-bus code.  Get the 'unique_name' to ensure the bus is up far
    // enough to avoid the assert.
    if (b != nullptr)
    {
        get_unique_name();
    }
}

因此:

_intf = &sdbus_impl,
_bus = _intf->sd_bus_ref(b)

在文件build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/sdbus.hpp:中可以看到:

class SdBusImpl : public SdBusInterface
{
int sd_bus_add_object_manager(...)
int sd_bus_add_object_vtable(...)
int sd_bus_add_match(...)
int sd_bus_attach_event( ...)
int sd_bus_call(...)
int sd_bus_call_async(...)
int sd_bus_detach_event(...)
int sd_bus_emit_interfaces_added_strv(...)
...
int sd_bus_emit_object_added(...)
int sd_bus_get_fd(...)
int sd_bus_message_enter_container(...)
sd_bus* sd_bus_message_get_bus(...)
const char* sd_bus_message_get_interface(...)
const char* sd_bus_message_get_path(...)
int sd_bus_message_is_method_call(..)
int sd_bus_message_new_method_call(...)
int sd_bus_message_new_signal(...)
int sd_bus_process(...)
int sd_bus_request_name(...)
void sd_bus_close(...)
int sd_bus_is_open(...)
int sd_bus_wait(...)
}
extern SdBusImpl sdbus_impl;

以及文件:build/evb-ast2500/workspace/sources/sdbusplus/src/sdbus.cpp中定义的:

#include <sdbusplus/sdbus.hpp>

namespace sdbusplus
{
SdBusImpl sdbus_impl;
}

包含的均为sd-bus接口的调用封装。

注意函数read_immediate()调用函数:

    void read_immediate()
    {
        boost::asio::post(io_, [&] {
            if (process_discard())
            {
                read_immediate();
            }
            else
            {
                read_wait();
            }
        });
    }

因此，函数调用:

conn->request_name(busServiceName.c_str());

实际执行了文件build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/bus.hpp中的:

    void request_name(const char* service)
    {
        int r = _intf->sd_bus_request_name(
            _bus.get(), service,
            (SD_BUS_NAME_ALLOW_REPLACEMENT | SD_BUS_NAME_REPLACE_EXISTING));
        if (r < 0)
        {
            throw exception::SdBusError(-r, "sd_bus_request_name");
        }
    }

qemu启动之后，可以看到这个例子只是一个简单的例子，并无实际的意义，因为并不能找到相关的接口功能。执行结果如下:

2.2 添加接口

添加接口与相关的属性，才具初始的功能。

先分析2行代码:

    sdbusplus::asio::object_server obj_server = sdbusplus::asio::object_server(conn);
    Iface = obj_server.add_interface("/org/freedesktop" , busServiceName); 
    Iface->initialize();

在文件:build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/asio/object_server.hpp中定义了:

    object_server(const std::shared_ptr<sdbusplus::asio::connection>& conn,
                  const bool skipManager = false) : conn_(conn)
    {
        if (!skipManager)
        {
            add_manager("/");
        }
    }

因此默认skipManager = false，会调用add_manager("/");

Iface = obj_server.add_interface("/org/freedesktop" , busServiceName);

调用文件:build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/asio/object_server.hpp中的函数:

    std::shared_ptr<dbus_interface>
        add_interface(const std::string& path, const std::string& name)
    {
        auto dbusIface = std::make_shared<dbus_interface>(conn_, path, name);
        interfaces_.emplace_back(dbusIface);
        return dbusIface;
    }

只需要注意:interfaces_是被定义在类中的私有变量:

  private:
    std::shared_ptr<sdbusplus::asio::connection> conn_;
    std::vector<std::shared_ptr<dbus_interface>> interfaces_;
    std::vector<server::manager_t> managers_;

另外，dbus_interface有在build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/asio/object_server.hpp中定义了:

    dbus_interface(std::shared_ptr<sdbusplus::asio::connection> conn,
                   const std::string& path, const std::string& name) :
        conn_(conn), path_(path), name_(name)

    {}

所以，在这里只完成了基本的赋值与将定义的接口放入vector(数组)中。

最后，需要调用:Iface->initialize();，可以看到调用了文件build/evb-ast2500/workspace/sources/sdbusplus/include/sdbusplus/asio/object_server.hpp中的:

    bool initialize(const bool skipPropertyChangedSignal = false)
    {
        // can only register once
        if (is_initialized())
        {
            return false;
        }
        vtable_.reserve(2 + property_callbacks_.size() +
                        method_callbacks_.size() + signals_.size());
        vtable_.emplace_back(vtable::start());
        property_callbacks_.shrink_to_fit();
        for (auto& element : property_callbacks_)
        {
            if (element.on_set_message_)
            {
                vtable_.emplace_back(vtable::property_o(
                    element.name_.c_str(), element.signature_, get_handler,
                    set_handler, reinterpret_cast<size_t>(&element),
                    element.flags_ | SD_BUS_VTABLE_ABSOLUTE_OFFSET));
            }
            else
            {
                vtable_.emplace_back(vtable::property_o(
                    element.name_.c_str(), element.signature_, get_handler,
                    reinterpret_cast<size_t>(&element),
                    element.flags_ | SD_BUS_VTABLE_ABSOLUTE_OFFSET));
            }
        }

        method_callbacks_.shrink_to_fit();
        for (auto& element : method_callbacks_)
        {
            vtable_.emplace_back(vtable::method_o(
                element.name_.c_str(), element.arg_signature_,
                element.return_signature_, method_handler,
                reinterpret_cast<size_t>(&element),
                element.flags_ | SD_BUS_VTABLE_ABSOLUTE_OFFSET));
        }

        signals_.shrink_to_fit();
        for (const auto& element : signals_)
        {
            vtable_.emplace_back(
                vtable::signal(element.name_.c_str(), element.signature_));
        }

        vtable_.emplace_back(vtable::end());
        vtable_.shrink_to_fit();

        interface_.emplace(static_cast<sdbusplus::bus_t&>(*conn_),
                           path_.c_str(), name_.c_str(),
                           static_cast<const sd_bus_vtable*>(&vtable_[0]),
                           nullptr);
        conn_->emit_interfaces_added(path_.c_str(),
                                     std::vector<std::string>{name_});
        if (!skipPropertyChangedSignal)
        {
            for (const auto& element : property_callbacks_)
            {
                signal_property(element.name_);
            }
        }
        return true;
    }

另外，分析一下内容:

vtable_.reserve(2 + property_callbacks_.size() +
                        method_callbacks_.size() + signals_.size());

可以看到代码是在vtable是针对property、method、signals的执行操作，由于SD_BUS_VTABLE_START(0)和SD_BUS_VTABLE_END占用2个空间，故加2。

这一节的代码参考: https://gitee.com/wit_yuan/openbmc_testcode/blob/yuan_add_interface/recipe-example/files/test_add_interface.cpp

需要之前的hello服务器程序运行起来。

同样，可以看到设置和获取property值的变化: