| commit | a0fe02cad6645d0cd9328db414758d3f2f921663 | [log] [tgz] |
|---|---|---|
| author | Alexander Hansen <alexander.hansen@9elements.com> | Mon Mar 10 18:26:56 2025 +0100 |
| committer | Patrick Williams <patrick@stwcx.xyz> | Tue Jun 17 23:05:59 2025 -0400 |
| tree | 69b87d2508bc8569ef5cf64f1e0a283f86bb35fa | |
| parent | c63e8e8ac5af1334b18aa7750341b3579979efb3 [diff] |
aserver: constructor to initialize properties Functions like 'emit_added()' do not work correctly if properties are not initialized. Often, the initial values for the properties of an interface are known, such as - Software Version Interface - Software ActivationProgress Interface - Software ApplyTime Interface - ... How was this previously handled? - Write a wrapper class for the specific aserver class. This allows to initialize the properties, as they are protected members. Example [2] - Write a wrapper class and provide methods to get/set the variables. This is done in [1] - Set each property with a method call, which emits 'PropertyChanged' signal by default, not ideal. This also does not work if the interface is ever refactored to have additional properties. To facilitate using these interfaces without having to write a wrapper class to inherit from them, and to avoid having to manually set each property, which can easily be forgotten, provide a constructor to allow for passing a struct with values for all the properties. Tested: Unit tests pass, but still needs to be build-tested against openbmc/openbmc. The concern there is mostly due to an added template parameter. References: [1] https://github.com/openbmc/sdbusplus/blob/da8574d5888b2c1622f5482a47adc7a12ffa0d0e/example/calculator-aserver.cpp#L44 [2] https://github.com/openbmc/phosphor-bmc-code-mgmt/blob/4983b138ea8fc70bd66fe4d30500e6252629fa5d/common/src/software.cpp#L29 Change-Id: I873cbca97ae16b19bfbf622303f4d52e2563a62c Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com> Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
sdbusplus contains two parts:
The sdbusplus library requires sd-bus, which is contained in libsystemd.
The sdbus++ application requires Python 3 and the Python libraries mako and inflection.
The sdbusplus library is built using meson.
meson build
cd build
ninja
ninja test
ninja install
Optionally, building the tests and examples can be disabled by passing -Dtests=disabled and -Dexamples=disabled respectively to meson.
The sdbus++ application is installed as a standard Python package using setuptools.
cd tools ./setup.py install
The sdbusplus library builds on top of the sd-bus library to create a modern C++ API for D-Bus. The library attempts to be as lightweight as possible, usually compiling to exactly the sd-bus API calls that would have been necessary, while also providing compile-time type-safety and memory leak protection afforded by modern C++ practices.
Consider the following code:
auto b = bus::new_default_system(); auto m = b.new_method_call("org.freedesktop.login1", "/org/freedesktop/login1", "org.freedesktop.login1.Manager", "ListUsers"); auto reply = b.call(m); std::vector<std::tuple<uint32_t, std::string, message::object_path>> users; reply.read(users); // or auto users = reply.unpack< std::vector<std::tuple<uint32_t, std::string, message::object_path>>>();
In a few, relatively succinct, C++ lines this snippet will create a D-Bus connection to the system bus, and call the systemd login manager to get a list of active users. The message and bus objects are automatically freed when they leave scope and the message format strings are generated at compile time based on the types being read. Compare this to the corresponding server code within logind.
In general, the library attempts to mimic the naming conventions of the sd-bus library: ex. sd_bus_call becomes sdbusplus::bus::call, sd_bus_get_unique_name becomes sdbusplus::bus::get_unique_name, sd_bus_message_get_signature becomes sdbusplus::message::get_signature, etc. This allows a relatively straight-forward translation back to the sd-bus functions for looking up the manpage details.
sdbusplus also contains a bindings generator tool: sdbus++. The purpose of a bindings generator is to reduce the boilerplate associated with creating D-Bus server or client applications. When creating a server application, rather than creating sd-bus vtables and writing C-style functions to handle each vtable callback, you can create a small YAML file to define your D-Bus interface and the sdbus++ tool will create a C++ class that implements your D-Bus interface. This class has a set of virtual functions for each method and property, which you can overload to create your own customized behavior for the interface.
There are currently two types of YAML files: interface and error. Interfaces are used to create server and client D-Bus interfaces. Errors are used to define C++ exceptions which can be thrown and will automatically turn into D-Bus error responses.
[[D-Bus client bindings are not yet implemented. See openbmc/openbmc#851.]]
The path of your file will be the interface name. For example, for an interface org.freedesktop.Example, you would create the files org/freedesktop/Example.interface.yaml and org/freedesktop/Example.errors.yaml] for interfaces and errors respectively. These can then be used to generate the server and error bindings:
sdbus++ interface server-header org.freedesktop.Example > \ org/freedesktop/Example/server.hpp sdbus++ interface server-cpp org.freedesktop.Example > \ org/freedesktop/Example/server.cpp sdbus++ error exception-header org.freedesktop.Example > \ org/freedesktop/Example/error.hpp \ sdbus++ error exception-cpp org.freedesktop.Example > \ org/freedesktop/Example/error.cpp
Markdown-based documentation can also be generated from the interface and exception files:
sdbus++ interface markdown org.freedesktop.Example > \ org/freedesktop/Example.md sdbus++ error markdown org.freedesktop.Example >> \ org/freedesktop/Example.md
See the example/meson.build for more details.
Installation of sdbusplus bindings on a custom distribution requires a few packages to be installed prior. Although these packages are the same for several distributions the names of these packages do differ. Below are the packages needed for Ubuntu and Fedora.
sudo apt install git meson libtool pkg-config g++ libsystemd-dev \ python3 python3-pip python3-yaml python3-mako python3-inflection
sudo dnf install git meson libtool gcc-c++ pkgconfig systemd-devel \ python3 python3-pip python3-yaml python3-mako
Install the inflection package using the pip utility (on Fedora)
pip3 install inflection