| commit | 242677a2b3dafdb3b79464eb64e0ae8bc7c5a7d5 | [log] [tgz] |
|---|---|---|
| author | Ed Tanous <ed@tanous.net> | Wed Mar 27 17:56:21 2024 -0700 |
| committer | Ed Tanous <ed@tanous.net> | Tue Jul 08 16:20:25 2025 +0000 |
| tree | 40e2bc1fe70e520a2950c887c563cd8a16cbd763 | |
| parent | f4265a78d12cc2d2a8d17d7ac0367d785cbfbf52 [diff] |
Use sd-bus array methods for read and append Currently sdbusplus uses sd_bus_message_read_basic and message_append_basic for decoding and encoding of arrays. For large arrays, this imposes a significant overhead in calling the library each time. This leads to some extreme performance degradation in some cases, for example, passing a 4K bytes data array over sdbusplus interface now takes 4096 + 2 calls of sd_bus_message_read_basic and message_append_basic, this will consume about 10ms CPU time on a Aspeed 2600 platform for each package on both send and receive side. While in this case, a DBus interface design should likely opt for using an FD rather than an array of bytes, this isn't a reason to not optimize this case. sd-bus, in version 240 added methods to deal with this performance degradation, namely sd_bus_message_read_array and sd_bus_message_append_array, which each only require a single call to load values into the array using pointers and lengths. This patchset is based on the one submitted here: https://gerrit.openbmc.org/c/openbmc/sdbusplus/+/68614 But opts for a different approach to a number of technical details on how it accomplishes the result, including changing the underlying sd-bus calls used to utilize ones that don't require sdbus internal malloc, avoiding unit tests ASAN issues in the process. This commit adds support for utilizing the above methods when doing calls to the library if the following requirements are met: 1. The container is contiguous (using the std::contiguous_iterator concept) 2. The container represents a list of values of type int/uint 8,16,32, or 64 bits wide. Note, per the sd-bus documentation, arrays of bool are explicitly not supported (presumably because the internal representation of a bool array for both libc++ and sd-bus is implementation defined). To accomplish this, the arrays handling for contiguous arrays is moved to use concepts, simplifying the code significantly, and allowing the use of std::contiguous_iterator. Change-Id: I3bd9f97ed160835e8c30c302b80553a1d450bbf9 Signed-off-by: Ed Tanous <ed@tanous.net> Signed-off-by: Yongbing Chen <yongbingchen@google.com>
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