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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 24d8c1a..e61e67f 100644 --- a/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md +++ b/docs/04_Developer_Guides/01_Application_Framework/01_Introduction.md @@ -4,49 +4,63 @@ title: Introduction # Foreword -The AGL Application Framework is nothing new. However, the implementation used up until -the `lamprey` release has been retired starting with the `marlin` release and replaced -by a redesigned Application Framework one. However, this new implementation isn't a 1:1 -replacement, and as such it doesn't provide all of the features of the previous -Application Framework. Some of those will be added back over time, others have been -discarded in favor of more modern and/or widely-used alternatives. +The AGL Application Framework is nothing new. However, the implementation used +up until the `lamprey` release has been retired starting with the `marlin` +release and replaced by a redesigned Application Framework one. However, this +new implementation isn't a 1:1 replacement, and as such it doesn't provide all +of the features of the previous Application Framework. Some of those will be +added back over time, others have been discarded in favor of more modern and/or +widely-used alternatives. + +With `needlefish` release, further changes have been added, including a gRPC +interface, alongside a D-BUs one, as well as using systemd units to start +applications. + # Introduction -As a provider of an integrated solution to build up on, AGL needs to define a reliable -and well-specified method for managing the deployment and integration of applications -and services, as well as the way they can interact with the rest of the system. +As a provider of an integrated solution to build up on, AGL needs to define a +reliable and well-specified method for managing the deployment and integration +of applications and services, as well as the way they can interact with the +rest of the system. -This is achieved by providing a common set of rules and components, known as the -Application Framework. By ensuring conformity to those rules, application developers -can have a good understanding of the requirements for creating and packaging -applications targeting AGL-based systems. Likewise, system developers and integrators -have a clear path for including such applications in AGL-based products. +This is achieved by providing a common set of rules and components, known as +the Application Framework. By ensuring conformity to those rules, application +developers can have a good understanding of the requirements for creating and +packaging applications targeting AGL-based systems. Likewise, system developers +and integrators have a clear path for including such applications in AGL-based +products. The Application Framework's scope extends to the following areas: - system services integration and lifecycle management -- user session management, including user-level applications and services lifecycle - management +- user session management, including user-level applications and services + lifecycle management - inter-process communication -In order to be as simple as possible and avoid any unneded custom implementation, the -Application Framework relies mainly on third-party technologies and/or software -components, most of those being maintained under the -[freedesktop.org](https://www.freedesktop.org) umbrella. Those include: +In order to be as simple as possible and avoid any unneded custom +implementation, the Application Framework relies mainly on third-party +technologies and/or software components, most of those being maintained under +the [freedesktop.org](https://www.freedesktop.org) umbrella. Those include: + +- [systemd](https://www.freedesktop.org/wiki/Software/systemd/): system + services and user session services management -- [systemd](https://www.freedesktop.org/wiki/Software/systemd/): system services and user session services management +- [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/): inter-process + communication, now in deprecated phase. -- [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/): inter-process communication +- [gRPC](https://grpc.io/about): inter-process communication - [Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/): - application enumeration and startup + application enumeration and startup, now in deprecated phase, systemd being + the one would list out applications and handling start-up. -AGL also provides reference implementations whenever possible and relevant, located in -the [meta-agl](/04_Developer_Guides/02_AGL_Layers/02_meta_agl/) layer under `meta-app-framework`. At the -moment, the Application Framework contains 2 such components: +AGL also provides reference implementations whenever possible and relevant, +located in the [meta-agl](/04_Developer_Guides/02_AGL_Layers/02_meta_agl/) +layer under `meta-app-framework`. At the moment, the Application Framework +contains 2 such components: - `agl-session`: `systemd` unit files for user sessions management @@ -54,56 +68,59 @@ moment, the Application Framework contains 2 such components: # Services management -Both system and user services are managed by `systemd`, which provides a number of -important features, such as dependency management or service monitoring: when starting -a service, `systemd` will ensure any other units this service depends on are available, -and otherwise start those dependencies. Similarly, `systemd` can automatically restart -a crashed service, ensuring minimal downtime. +Both system and user services are managed by `systemd`, which provides a number +of important features, such as dependency management or service monitoring: +when starting a service, `systemd` will ensure any other units this service +depends on are available, and otherwise start those dependencies. Similarly, +`systemd` can automatically restart a crashed service, ensuring minimal +downtime. `systemd` also provides an efficient first layer of security through its [sandboxing](https://www.freedesktop.org/software/systemd/man/systemd.exec.html#Sandboxing) and other security-related options. -It is also well integrated with D-Bus and can be used for a more fine-grained control -over D-Bus activated services: by delegating the actual service startup to `systemd`, -developers can take advantage of some of its advanced features, allowing for improved -reliability and security. +It is also well integrated with D-Bus and can be used for a more fine-grained +control over D-Bus activated services: by delegating the actual service startup +to `systemd`, developers can take advantage of some of its advanced features, +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. +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. # User session management -Similarly, user sessions and the services they rely on are also managed by `systemd`. +Similarly, user sessions and the services they rely on are also managed by +`systemd`. AGL provides 2 `systemd` units: -1\. `agl-session@.service` is a template system service for managing user sessions; it -takes a username or UID as a parameter, creating a session for the desired user. -Instanciating this service can be achieved by enabling `agl-session@USER.service`, for -example by executing the following command on a running system: +1\. `agl-session@.service` is a template system service for managing user +sessions; it takes a username or UID as a parameter, creating a session for the +desired user. Instanciating this service can be achieved by enabling +`agl-session@USER.service`, for example by executing the following command on a +running system: ``` $ systemctl enable agl-session@USER.service ``` -By default, AGL enables this service as `agl-session@agl-driver.service`, running as -user `agl-driver`. +By default, AGL enables this service as `agl-session@agl-driver.service`, +running as user `agl-driver`. -*Note: while you can create sessions for as many users as needed, only one instance of -`agl-session@.service` is allowed per user.* +*Note: while you can create sessions for as many users as needed, only one +instance of `agl-session@.service` is allowed per user.* 2\. `agl-session.target` is a user target for managing user services and their dependencies. It is started by `agl-session@.service`. -By default, `agl-compositor` is part of this target. It is therefore automatically -started for user `agl-driver`. +By default, `agl-compositor` is part of this target. It is therefore +automatically started for user `agl-driver`. -Any other service needed as part of the user session should similarly depend on this -target by appending the following lines to their unit file: +Any other service needed as part of the user session should similarly depend on +this target by appending the following lines to their unit file: ``` [Install] @@ -112,39 +129,48 @@ WantedBy=agl-session.target # Inter-process communication -In order to provide a "standard", language-independent IPC mechanism and avoid the need -for maintaining custom bindings for each programming language to be used on top of AGL, -the Application Framework promotes the use of [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/) -as the preferred way for applications to interact with services. +In order to provide a "standard", language-independent IPC mechanism and avoid +the need for maintaining custom bindings for each programming language to be +used on top of AGL, the Application Framework used to promote the use of +[D-Bus](https://www.freedesktop.org/wiki/Software/dbus/) as the preferred way +for applications to interact with services. Starting with `needlefish` release +we instead switched to using [gRPC](https://grpc.io) for our system-wide IPC, +with D-Bus being kept to provide functionality to services and application +which haven't transitioned yet to using gRPC. -Most services already included in AGL provide one or several D-Bus interfaces, and can -therefore interact with D-Bus capable applications and services without requiring any -additional component. Those services include, among others: +Most services already included in AGL provide one or several D-Bus interfaces, +and can therefore interact with D-Bus capable applications and services +without requiring any additional component. Those services include, among +others: -- [ConnMan](https://git.kernel.org/pub/scm/network/connman/connman.git/): network connectivity +- [ConnMan](https://git.kernel.org/pub/scm/network/connman/connman.git/): + network connectivity - [BlueZ](http://www.bluez.org/): Bluetooth connectivity -- [oFono](https://git.kernel.org/pub/scm/network/ofono/ofono.git): telephony and modem - management +- [oFono](https://git.kernel.org/pub/scm/network/ofono/ofono.git): telephony + and modem management -- [GeoClue](https://gitlab.freedesktop.org/geoclue/geoclue/-/wikis/home): geolocation +- [GeoClue](https://gitlab.freedesktop.org/geoclue/geoclue/-/wikis/home): + geolocation # Application launcher service -As mentioned above, the Application Framework follows the guidelines of the +The Application Framework used to follow the guidelines of the [Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/) -for application enumeration and startup. +for application enumeration and startup, but now instead relies on systemd to +provide that functionality indirectly, using the `applaunchd` application. -As no simple reference implementation exists for this part of the specification, AGL -provides an application launcher service named `applaunchd`. This service is part of the -default user session, and as such is automatically started on session startup. It can -therefore be considered always available. +As no simple reference implementation exists for this part of the +specification, AGL provides an application launcher service named `applaunchd`. +This service is part of the default user session, and as such is automatically +started on session startup. It can therefore be considered always available. -`applaunchd` enumerates applications installed on the system and provides a D-bus -interface for services and applications to: +`applaunchd` enumerates applications installed on the system and provides a +D-bus (deprecated)/gRPC interface for services and applications to: - query the list of available applications - request the startup and/or activation of a specific application - be notified when applications are started or terminated -`applaunchd` is described with more details in [the following document](../02_Application_Startup/). +`applaunchd` is described with more details in +[the following document](../02_Application_Startup/). |