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Diffstat (limited to 'docs/04_Developer_Guides/01_Application_Framework')
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diff --git a/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md b/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md index e61e67f..5c38907 100644 --- a/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md +++ b/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md @@ -86,7 +86,7 @@ allowing for improved reliability and security. Each service should be represented by a `systemd` unit file installed to the appropriate location. More details can be obtained from the [Creating a New -Service](/04_Developer_Guides/02_Creating_a_New_Service/) document. +Service](../03_Creating_a_New_Service/) document. # User session management diff --git a/docs/04_Developer_Guides/01_Application_Framework/03_Creating_a_New_Service.md b/docs/04_Developer_Guides/01_Application_Framework/03_Creating_a_New_Service.md new file mode 100644 index 0000000..22e98ea --- /dev/null +++ b/docs/04_Developer_Guides/01_Application_Framework/03_Creating_a_New_Service.md @@ -0,0 +1,151 @@ +--- +title: Creating a New Service +--- + +Services are software running in the background and providing, as their name suggests, +various services to other software: access to specific system hardware, connectivity +management, and network servers. Services can be split into 2 categories: + +- **System services:** those usually run as a privileged user and make use of shared system + resources which they should have exclusive access to + +- **User services:** such services run as part of an unprivileged user's session and can + only be called by said user + +# Basic requirements + +The only mandatory requirement is that service packages provide a `.service` file +so they can be properly managed by `systemd`. This file must be installed to a specific +location, determined by the service type (system or user): + +- `/usr/lib/systemd/system/` for system services + +- `/usr/lib/systemd/user/` for user services + +Below is an example of a simple user service, running in a graphical session and +therefore requiring a compositor to be already running before the service starts: + +``` +[Unit] +Requires=agl-compositor.service +After=agl-compositor.service + +[Service] +Type=simple +ExecStart=/usr/bin/homescreen +Restart=on-failure + +[Install] +WantedBy=agl-session.target +``` + +The `WantedBy=agl-session.target` indicates the service is part of the default AGL +user session, as mentioned in the [Application Framework](../01_Application_Framework/01_Introduction/#user-session-management) +documentation. + +The `Restart=on-failure` directive ensures the service will be automatically +restarted by `systemd` in case it crashes. + +More details about `systemd` service files can be found in the +[systemd documentation](https://www.freedesktop.org/software/systemd/man/systemd.service.html). + +# D-Bus activation + +Services can also provide a D-Bus interface. In this case, they need not be started +on system boot (or user session startup in the case of user services) but can be +automatically started only when a client sends a request to the D-Bus name the service +registers. + +D-Bus activated services must name their `systemd` service file `dbus-NAME.service` +where `NAME` is the D-Bus name registered by the service. This file must include the +following lines: + +``` +[Service] +Type=dbus +BusName=NAME +ExecStart=/path/to/executable +``` + +In addition, they must provide a D-Bus service file named `NAME.service` and installed +to one of the following locations: + +- `/usr/share/dbus-1/system-services` for system services + +- `/usr/share/dbus-1/services` for user services + +The contents of the D-Bus service file must be the following: + +``` +[D-BUS Service] +Name=NAME +Exec=/path/to/executable +SystemdService=dbus-NAME.service +``` + +This ensures the service can be safely activated through D-Bus and no conflict will occur +between `systemd` and the D-Bus daemon. + +More details about D-Bus activation can be found in the +[D-Bus specification](https://dbus.freedesktop.org/doc/dbus-specification.html#message-bus-starting-services), +under the "Message Bus Starting Services (Activation)" section. + +# Services startup + +For D-Bus activated services, no additional action is required as those will be automatically +started whenever needed. Other services, however, need a few more steps in order to be +executed on system or session startup. + +## System services + +System services can take advantage of the Yocto `systemd` class which automates the process of +enabling such services. + +1\. Ensure the recipe inherits from the `systemd` class: + +``` +inherit systemd +``` + +2\. Declare the system services that needs to be enabled on boot: + +``` +SYSTEMD_SERVICE:${PN} = "NAME.service" +``` + +3\. Ensure the `FILES` variable includes the systemd service directory the corresponding +file will be installed to: + +``` +FILES:${PN} = "\ + ... + ${systemd_system_unitdir}/* \ +" +``` + +## User services + +The `systemd` class doesn't provide an equivalent mechanism for user services. This must +therefore be done manually as part of the package's install process. + +1\. Make the service a part of the user session: + +``` +do_install:append() { + install -d ${D}${systemd_user_unitdir}/agl-session.target.wants + ln -s ../NAME.service ${D}${systemd_user_unitdir}/agl-session.target.wants/NAME.service +} +``` + +This ensures `agl-session.target` depends on `NAME.service`, the latter being therefore +automatically started on session creation. + +2\. Ensure the `FILES` variable includes the systemd service directory the corresponding +file will be installed to: + +``` +FILES:${PN} = "\ + ... + ${systemd_user_unitdir}/* \ +" +``` diff --git a/docs/04_Developer_Guides/01_Application_Framework/04_Creating_a_New_Application.md b/docs/04_Developer_Guides/01_Application_Framework/04_Creating_a_New_Application.md new file mode 100644 index 0000000..014069d --- /dev/null +++ b/docs/04_Developer_Guides/01_Application_Framework/04_Creating_a_New_Application.md @@ -0,0 +1,135 @@ +--- +title: Creating a New Application +--- + +Applications are: + +- Software designed to perform a specific task during a limited amount of time. +- Graphical interface allowing user to interact with. + +Applications are executed by `applaunchd`, the AGL +[application launcher service](../01_Application_Framework/02_Application_Startup/). + +# Basic requirements + +In order to be enumerated by `applaunchd`, applications must provide the a `.desktop` file, as +defined by the [Desktop Entry specification](https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html). + +The desktop entry file should be installed to `/usr/share/applications` (or the `applications` +sub-directory of any entry present in the `XDG_DATA_DIRS` environment variable) and have a +meaningful name. It is considered good practice to use reverse-DNS notation for the desktop +entry file name, following the recommendations of the [D-Bus specification](https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names): +- this avoids potential name collisions with other desktop entry files +- it makes it easier to enable [D-Bus activation](#d-bus-activation) during the application + development cycle if needed +- for [graphical applications](#graphical-applications), it ensures the chosen Wayland `app-id` + will be unique + +Such a file must contain at least the following keys: +- `Type`: desktop entry type, must be set to `Application` +- `Name`: application name, as it should be displayed in menus and application launchers +- `Exec`: full path to the main executable + +Below is an example of a minimal desktop entry file: + +``` +[Desktop Entry] +Type=Application +Name=Example Application +Exec=/usr/bin/example-app +``` + +Graphical applications must also provide an `Icon` entry pointing to the application icon. +The value for this entry must either be the full path to the icon's file or, for icons part +of an existing [icon theme](https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html), +the name of an element of this theme. + +In addition, a number of optional fields can be used to change how `applaunchd` will consider the +application: +- `Version`: version of the Desktop Entry Specification the file conforms to, must be `1.5` +- `Hidden`: boolean value, if `true` the application is always ignored by `applaunchd` and + won't be listed nor executed +- `Terminal`: boolean value, if `true` the application is excluded when requesting the list of + graphical applications from `applaunchd` +- `DBusActivatable`: boolean value, must be `true` for [D-Bus activated applications](#d-bus-activation) +- `Implements`: list of D-Bus interfaces the application implements, only used for D-Bus activated + applications. + +Finally, graphical applications may also define the `StartupWMClass` key in some cases. Please +refer to the [graphical applications](#graphical-applications) section for more information. + +# D-Bus activation + +Similarly to [services](../02_Creating_a_New_Service/#d-bus-activation), applications can +also be activated through D-Bus. + +Such applications must name their `.desktop` file after the D-Bus name they register. In addition, +this file must contain the following entries: + +``` +DBusActivatable=true +Implements=IFACE1;IFACE2;... +``` + +Where `IFACEn` are the names of the D-Bus interfaces the application implements. + +In addition, they must provide a D-Bus service file named `NAME.service` and installed +to `/usr/share/dbus-1/services`. + +The contents of the D-Bus service file must be the following: + +``` +[D-BUS Service] +Name=NAME +Exec=/path/to/executable +``` + +For example, an application registering the `org.automotivelinux.Example` D-Bus name +and implementing the `org.automotivelinux.Example.Search1` and `org.automotivelinux.Example.Execute1` +interfaces would provide the following files: + +* Desktop entry (`/usr/share/applications/org.automotivelinux.Example.desktop`): + +``` +[Desktop Entry] +Type=Application +Version=1.5 +Name=Example Application +Exec=/usr/bin/example-app +Icon=example-icon +Terminal=false +DBusActivatable=true +Implements=org.automotivelinux.Example.Search1;org.automotivelinux.Example.Execute1 +``` + +* D-Bus service file (`/usr/share/dbus-1/services/org.automotivelinux.Example.service`): + +``` +[D-BUS Service] +Name=org.automotivelinux.Example +Exec=/usr/bin/example-app +``` + +*Note: in addition to their own D-Bus interface, D-Bus activated applications must also +implement the `org.freedesktop.Application` interface as defined in the +[Desktop Entry specification](https://specifications.freedesktop.org/desktop-entry-spec/1.1/ar01s07.html).* + +# Graphical applications + +In addition, graphical applications need to comply with a few more requirements: + +1\. Each application must set a Wayland application ID appropriately as soon as its main window +is created. + +2\. The `app-id` must be specified in the desktop entry file by adding the following line: + +``` +StartupWMClass=APP_ID +``` + +3\. The desktop entry file must be named `APP_ID.desktop`. + +Doing so will ensure other software can associate the actual `app-id` to the proper application. + +*Note: application ID's are set using the [XDG toplevel](https://wayland-book.com/xdg-shell-basics/xdg-toplevel.html) +Wayland interface.* |