poky/documentation/ref-manual/features.rst - mdmillerii/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-SA-2.0-UK

 ********
 Features
 ********

 This chapter provides a reference of shipped machine and distro features
 you can include as part of your image, a reference on image features you
 can select, and a reference on feature backfilling.

 Features provide a mechanism for working out which packages should be
 included in the generated images. Distributions can select which
 features they want to support through the ``DISTRO_FEATURES`` variable,
 which is set or appended to in a distribution's configuration file such
 as ``poky.conf``, ``poky-tiny.conf``, ``poky-lsb.conf`` and so forth.
 Machine features are set in the ``MACHINE_FEATURES`` variable, which is
 set in the machine configuration file and specifies the hardware
 features for a given machine.

 These two variables combine to work out which kernel modules, utilities,
 and other packages to include. A given distribution can support a
 selected subset of features so some machine features might not be
 included if the distribution itself does not support them.

 One method you can use to determine which recipes are checking to see if
 a particular feature is contained or not is to ``grep`` through the
 :term:`Metadata` for the feature. Here is an example that
 discovers the recipes whose build is potentially changed based on a
 given feature:
 ::

    $ cd poky
    $ git grep 'contains.*MACHINE_FEATURES.*feature'

 .. _ref-features-machine:

 Machine Features
 ================

 The items below are features you can use with
 :term:`MACHINE_FEATURES`. Features do not have a
 one-to-one correspondence to packages, and they can go beyond simply
 controlling the installation of a package or packages. Sometimes a
 feature can influence how certain recipes are built. For example, a
 feature might determine whether a particular configure option is
 specified within the :ref:`ref-tasks-configure` task
 for a particular recipe.

 This feature list only represents features as shipped with the Yocto
 Project metadata:

 -  *acpi:* Hardware has ACPI (x86/x86_64 only)

 -  *alsa:* Hardware has ALSA audio drivers

 -  *apm:* Hardware uses APM (or APM emulation)

 -  *bluetooth:* Hardware has integrated BT

 -  *efi:* Support for booting through EFI

 -  *ext2:* Hardware HDD or Microdrive

 -  *keyboard:* Hardware has a keyboard

 -  *pcbios:* Support for booting through BIOS

 -  *pci:* Hardware has a PCI bus

 -  *pcmcia:* Hardware has PCMCIA or CompactFlash sockets

 -  *phone:* Mobile phone (voice) support

 -  *qvga:* Machine has a QVGA (320x240) display

 -  *rtc:* Machine has a Real-Time Clock

 -  *screen:* Hardware has a screen

 -  *serial:* Hardware has serial support (usually RS232)

 -  *touchscreen:* Hardware has a touchscreen

 -  *usbgadget:* Hardware is USB gadget device capable

 -  *usbhost:* Hardware is USB Host capable

 -  *vfat:* FAT file system support

 -  *wifi:* Hardware has integrated WiFi

 .. _ref-features-distro:

 Distro Features
 ===============

 The items below are features you can use with
 :term:`DISTRO_FEATURES` to enable features across
 your distribution. Features do not have a one-to-one correspondence to
 packages, and they can go beyond simply controlling the installation of
 a package or packages. In most cases, the presence or absence of a
 feature translates to the appropriate option supplied to the configure
 script during the :ref:`ref-tasks-configure` task for
 the recipes that optionally support the feature.

 Some distro features are also machine features. These select features
 make sense to be controlled both at the machine and distribution
 configuration level. See the
 :term:`COMBINED_FEATURES` variable for more
 information.

 This list only represents features as shipped with the Yocto Project
 metadata:

 -  *alsa:* Include ALSA support (OSS compatibility kernel modules
    installed if available).

 -  *api-documentation:* Enables generation of API documentation during
    recipe builds. The resulting documentation is added to SDK tarballs
    when the ``bitbake -c populate_sdk`` command is used. See the
    ":ref:`sdk-manual/appendix-customizing-standard:adding api documentation to the standard sdk`"
    section in the Yocto Project Application Development and the
    Extensible Software Development Kit (eSDK) manual.

 -  *bluetooth:* Include bluetooth support (integrated BT only).

 -  *cramfs:* Include CramFS support.

 -  *directfb:* Include DirectFB support.

 -  *ext2:* Include tools for supporting for devices with internal
    HDD/Microdrive for storing files (instead of Flash only devices).

 -  *ipsec:* Include IPSec support.

 -  *ipv6:* Include IPv6 support.

 -  *keyboard:* Include keyboard support (e.g. keymaps will be loaded
    during boot).

 -  *ldconfig:* Include support for ldconfig and ``ld.so.conf`` on the
    target.

 -  *nfs:* Include NFS client support (for mounting NFS exports on
    device).

 -  *opengl:* Include the Open Graphics Library, which is a
    cross-language, multi-platform application programming interface used
    for rendering two and three-dimensional graphics.

 -  *pci:* Include PCI bus support.

 -  *pcmcia:* Include PCMCIA/CompactFlash support.

 -  *ppp:* Include PPP dialup support.

 -  *ptest:* Enables building the package tests where supported by
    individual recipes. For more information on package tests, see the
    ":ref:`dev-manual/common-tasks:testing packages with ptest`" section
    in the Yocto Project Development Tasks Manual.

 -  *smbfs:* Include SMB networks client support (for mounting
    Samba/Microsoft Windows shares on device).

 -  *systemd:* Include support for this ``init`` manager, which is a full
    replacement of for ``init`` with parallel starting of services,
    reduced shell overhead, and other features. This ``init`` manager is
    used by many distributions.

 -  *usbgadget:* Include USB Gadget Device support (for USB
    networking/serial/storage).

 -  *usbhost:* Include USB Host support (allows to connect external
    keyboard, mouse, storage, network etc).

 -  *usrmerge:* Merges the ``/bin``, ``/sbin``, ``/lib``, and ``/lib64``
    directories into their respective counterparts in the ``/usr``
    directory to provide better package and application compatibility.

 -  *wayland:* Include the Wayland display server protocol and the
    library that supports it.

 -  *wifi:* Include WiFi support (integrated only).

 -  *x11:* Include the X server and libraries.

 .. _ref-features-image:

 Image Features
 ==============

 The contents of images generated by the OpenEmbedded build system can be
 controlled by the :term:`IMAGE_FEATURES` and
 :term:`EXTRA_IMAGE_FEATURES` variables that
 you typically configure in your image recipes. Through these variables,
 you can add several different predefined packages such as development
 utilities or packages with debug information needed to investigate
 application problems or profile applications.

 The following image features are available for all images:

 -  *allow-empty-password:* Allows Dropbear and OpenSSH to accept root
    logins and logins from accounts having an empty password string.

 -  *dbg-pkgs:* Installs debug symbol packages for all packages installed
    in a given image.

 -  *debug-tweaks:* Makes an image suitable for development (e.g. allows
    root logins without passwords and enables post-installation logging).
    See the 'allow-empty-password', 'empty-root-password', and
    'post-install-logging' features in this list for additional
    information.

 -  *dev-pkgs:* Installs development packages (headers and extra library
    links) for all packages installed in a given image.

 -  *doc-pkgs:* Installs documentation packages for all packages
    installed in a given image.

 -  *empty-root-password:* Sets the root password to an empty string,
    which allows logins with a blank password.

 -  *package-management:* Installs package management tools and preserves
    the package manager database.

 -  *post-install-logging:* Enables logging postinstall script runs to
    the ``/var/log/postinstall.log`` file on first boot of the image on
    the target system.

    .. note::

       To make the ``/var/log`` directory on the target persistent, use the
       :term:`VOLATILE_LOG_DIR` variable by setting it to "no".

 -  *ptest-pkgs:* Installs ptest packages for all ptest-enabled recipes.

 -  *read-only-rootfs:* Creates an image whose root filesystem is
    read-only. See the
    ":ref:`dev-manual/common-tasks:creating a read-only root filesystem`"
    section in the Yocto Project Development Tasks Manual for more
    information.

 -  *splash:* Enables showing a splash screen during boot. By default,
    this screen is provided by ``psplash``, which does allow
    customization. If you prefer to use an alternative splash screen
    package, you can do so by setting the ``SPLASH`` variable to a
    different package name (or names) within the image recipe or at the
    distro configuration level.

 -  *staticdev-pkgs:* Installs static development packages, which are
    static libraries (i.e. ``*.a`` files), for all packages installed in
    a given image.

 Some image features are available only when you inherit the
 :ref:`core-image <ref-classes-core-image>` class. The current list of
 these valid features is as follows:

 -  *hwcodecs:* Installs hardware acceleration codecs.

 -  *nfs-server:* Installs an NFS server.

 -  *perf:* Installs profiling tools such as ``perf``, ``systemtap``, and
    ``LTTng``. For general information on user-space tools, see the
    :doc:`/sdk-manual/index` manual.

 -  *ssh-server-dropbear:* Installs the Dropbear minimal SSH server.

 -  *ssh-server-openssh:* Installs the OpenSSH SSH server, which is more
    full-featured than Dropbear. Note that if both the OpenSSH SSH server
    and the Dropbear minimal SSH server are present in
    ``IMAGE_FEATURES``, then OpenSSH will take precedence and Dropbear
    will not be installed.

 -  *tools-debug:* Installs debugging tools such as ``strace`` and
    ``gdb``. For information on GDB, see the
    ":ref:`dev-manual/common-tasks:debugging with the gnu project debugger (gdb) remotely`" section
    in the Yocto Project Development Tasks Manual. For information on
    tracing and profiling, see the :doc:`/profile-manual/index`.

 -  *tools-sdk:* Installs a full SDK that runs on the device.

 -  *tools-testapps:* Installs device testing tools (e.g. touchscreen
    debugging).

 -  *x11:* Installs the X server.

 -  *x11-base:* Installs the X server with a minimal environment.

 -  *x11-sato:* Installs the OpenedHand Sato environment.

 .. _ref-features-backfill:

 Feature Backfilling
 ===================

 Sometimes it is necessary in the OpenEmbedded build system to extend
 :term:`MACHINE_FEATURES` or
 :term:`DISTRO_FEATURES` to control functionality
 that was previously enabled and not able to be disabled. For these
 cases, we need to add an additional feature item to appear in one of
 these variables, but we do not want to force developers who have
 existing values of the variables in their configuration to add the new
 feature in order to retain the same overall level of functionality.
 Thus, the OpenEmbedded build system has a mechanism to automatically
 "backfill" these added features into existing distro or machine
 configurations. You can see the list of features for which this is done
 by finding the
 :term:`DISTRO_FEATURES_BACKFILL` and
 :term:`MACHINE_FEATURES_BACKFILL`
 variables in the ``meta/conf/bitbake.conf`` file.

 Because such features are backfilled by default into all configurations
 as described in the previous paragraph, developers who wish to disable
 the new features need to be able to selectively prevent the backfilling
 from occurring. They can do this by adding the undesired feature or
 features to the
 :term:`DISTRO_FEATURES_BACKFILL_CONSIDERED`
 or
 :term:`MACHINE_FEATURES_BACKFILL_CONSIDERED`
 variables for distro features and machine features respectively.

 Here are two examples to help illustrate feature backfilling:

 -  *The "pulseaudio" distro feature option*: Previously, PulseAudio
    support was enabled within the Qt and GStreamer frameworks. Because
    of this, the feature is backfilled and thus enabled for all distros
    through the ``DISTRO_FEATURES_BACKFILL`` variable in the
    ``meta/conf/bitbake.conf`` file. However, your distro needs to
    disable the feature. You can disable the feature without affecting
    other existing distro configurations that need PulseAudio support by
    adding "pulseaudio" to ``DISTRO_FEATURES_BACKFILL_CONSIDERED`` in
    your distro's ``.conf`` file. Adding the feature to this variable
    when it also exists in the ``DISTRO_FEATURES_BACKFILL`` variable
    prevents the build system from adding the feature to your
    configuration's ``DISTRO_FEATURES``, effectively disabling the
    feature for that particular distro.

 -  *The "rtc" machine feature option*: Previously, real time clock (RTC)
    support was enabled for all target devices. Because of this, the
    feature is backfilled and thus enabled for all machines through the
    ``MACHINE_FEATURES_BACKFILL`` variable in the
    ``meta/conf/bitbake.conf`` file. However, your target device does not
    have this capability. You can disable RTC support for your device
    without affecting other machines that need RTC support by adding the
    feature to your machine's ``MACHINE_FEATURES_BACKFILL_CONSIDERED``
    list in the machine's ``.conf`` file. Adding the feature to this
    variable when it also exists in the ``MACHINE_FEATURES_BACKFILL``
    variable prevents the build system from adding the feature to your
    configuration's ``MACHINE_FEATURES``, effectively disabling RTC
    support for that particular machine.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	********
	Features
	********

	This chapter provides a reference of shipped machine and distro features
	you can include as part of your image, a reference on image features you
	can select, and a reference on feature backfilling.

	Features provide a mechanism for working out which packages should be
	included in the generated images. Distributions can select which
	features they want to support through the ``DISTRO_FEATURES`` variable,
	which is set or appended to in a distribution's configuration file such
	as ``poky.conf``, ``poky-tiny.conf``, ``poky-lsb.conf`` and so forth.
	Machine features are set in the ``MACHINE_FEATURES`` variable, which is
	set in the machine configuration file and specifies the hardware
	features for a given machine.

	These two variables combine to work out which kernel modules, utilities,
	and other packages to include. A given distribution can support a
	selected subset of features so some machine features might not be
	included if the distribution itself does not support them.

	One method you can use to determine which recipes are checking to see if
	a particular feature is contained or not is to ``grep`` through the
	:term:`Metadata` for the feature. Here is an example that
	discovers the recipes whose build is potentially changed based on a
	given feature:
	::

	$ cd poky
	$ git grep 'contains.MACHINE_FEATURES.feature'

	.. _ref-features-machine:

	Machine Features
	================

	The items below are features you can use with
	:term:`MACHINE_FEATURES`. Features do not have a
	one-to-one correspondence to packages, and they can go beyond simply
	controlling the installation of a package or packages. Sometimes a
	feature can influence how certain recipes are built. For example, a
	feature might determine whether a particular configure option is
	specified within the :ref:`ref-tasks-configure` task
	for a particular recipe.

	This feature list only represents features as shipped with the Yocto
	Project metadata:

	- acpi: Hardware has ACPI (x86/x86_64 only)

	- alsa: Hardware has ALSA audio drivers

	- apm: Hardware uses APM (or APM emulation)

	- bluetooth: Hardware has integrated BT

	- efi: Support for booting through EFI

	- ext2: Hardware HDD or Microdrive

	- keyboard: Hardware has a keyboard

	- pcbios: Support for booting through BIOS

	- pci: Hardware has a PCI bus

	- pcmcia: Hardware has PCMCIA or CompactFlash sockets

	- phone: Mobile phone (voice) support

	- qvga: Machine has a QVGA (320x240) display

	- rtc: Machine has a Real-Time Clock

	- screen: Hardware has a screen

	- serial: Hardware has serial support (usually RS232)

	- touchscreen: Hardware has a touchscreen

	- usbgadget: Hardware is USB gadget device capable

	- usbhost: Hardware is USB Host capable

	- vfat: FAT file system support

	- wifi: Hardware has integrated WiFi

	.. _ref-features-distro:

	Distro Features
	===============

	The items below are features you can use with
	:term:`DISTRO_FEATURES` to enable features across
	your distribution. Features do not have a one-to-one correspondence to
	packages, and they can go beyond simply controlling the installation of
	a package or packages. In most cases, the presence or absence of a
	feature translates to the appropriate option supplied to the configure
	script during the :ref:`ref-tasks-configure` task for
	the recipes that optionally support the feature.

	Some distro features are also machine features. These select features
	make sense to be controlled both at the machine and distribution
	configuration level. See the
	:term:`COMBINED_FEATURES` variable for more
	information.

	This list only represents features as shipped with the Yocto Project
	metadata:

	- alsa: Include ALSA support (OSS compatibility kernel modules
	installed if available).

	- api-documentation: Enables generation of API documentation during
	recipe builds. The resulting documentation is added to SDK tarballs
	when the ``bitbake -c populate_sdk`` command is used. See the
	":ref:`sdk-manual/appendix-customizing-standard:adding api documentation to the standard sdk`"
	section in the Yocto Project Application Development and the
	Extensible Software Development Kit (eSDK) manual.

	- bluetooth: Include bluetooth support (integrated BT only).

	- cramfs: Include CramFS support.

	- directfb: Include DirectFB support.

	- ext2: Include tools for supporting for devices with internal
	HDD/Microdrive for storing files (instead of Flash only devices).

	- ipsec: Include IPSec support.

	- ipv6: Include IPv6 support.

	- keyboard: Include keyboard support (e.g. keymaps will be loaded
	during boot).

	- ldconfig: Include support for ldconfig and ``ld.so.conf`` on the
	target.

	- nfs: Include NFS client support (for mounting NFS exports on
	device).

	- opengl: Include the Open Graphics Library, which is a
	cross-language, multi-platform application programming interface used
	for rendering two and three-dimensional graphics.

	- pci: Include PCI bus support.

	- pcmcia: Include PCMCIA/CompactFlash support.

	- ppp: Include PPP dialup support.

	- ptest: Enables building the package tests where supported by
	individual recipes. For more information on package tests, see the
	":ref:`dev-manual/common-tasks:testing packages with ptest`" section
	in the Yocto Project Development Tasks Manual.

	- smbfs: Include SMB networks client support (for mounting
	Samba/Microsoft Windows shares on device).

	- systemd: Include support for this ``init`` manager, which is a full
	replacement of for ``init`` with parallel starting of services,
	reduced shell overhead, and other features. This ``init`` manager is
	used by many distributions.

	- usbgadget: Include USB Gadget Device support (for USB
	networking/serial/storage).

	- usbhost: Include USB Host support (allows to connect external
	keyboard, mouse, storage, network etc).

	- usrmerge: Merges the ``/bin``, ``/sbin``, ``/lib``, and ``/lib64``
	directories into their respective counterparts in the ``/usr``
	directory to provide better package and application compatibility.

	- wayland: Include the Wayland display server protocol and the
	library that supports it.

	- wifi: Include WiFi support (integrated only).

	- x11: Include the X server and libraries.

	.. _ref-features-image:

	Image Features
	==============

	The contents of images generated by the OpenEmbedded build system can be
	controlled by the :term:`IMAGE_FEATURES` and
	:term:`EXTRA_IMAGE_FEATURES` variables that
	you typically configure in your image recipes. Through these variables,
	you can add several different predefined packages such as development
	utilities or packages with debug information needed to investigate
	application problems or profile applications.

	The following image features are available for all images:

	- allow-empty-password: Allows Dropbear and OpenSSH to accept root
	logins and logins from accounts having an empty password string.

	- dbg-pkgs: Installs debug symbol packages for all packages installed
	in a given image.

	- debug-tweaks: Makes an image suitable for development (e.g. allows
	root logins without passwords and enables post-installation logging).
	See the 'allow-empty-password', 'empty-root-password', and
	'post-install-logging' features in this list for additional
	information.

	- dev-pkgs: Installs development packages (headers and extra library
	links) for all packages installed in a given image.

	- doc-pkgs: Installs documentation packages for all packages
	installed in a given image.

	- empty-root-password: Sets the root password to an empty string,
	which allows logins with a blank password.

	- package-management: Installs package management tools and preserves
	the package manager database.

	- post-install-logging: Enables logging postinstall script runs to
	the ``/var/log/postinstall.log`` file on first boot of the image on
	the target system.

	.. note::

	To make the ``/var/log`` directory on the target persistent, use the
	:term:`VOLATILE_LOG_DIR` variable by setting it to "no".

	- ptest-pkgs: Installs ptest packages for all ptest-enabled recipes.

	- read-only-rootfs: Creates an image whose root filesystem is
	read-only. See the
	":ref:`dev-manual/common-tasks:creating a read-only root filesystem`"
	section in the Yocto Project Development Tasks Manual for more
	information.

	- splash: Enables showing a splash screen during boot. By default,
	this screen is provided by ``psplash``, which does allow
	customization. If you prefer to use an alternative splash screen
	package, you can do so by setting the ``SPLASH`` variable to a
	different package name (or names) within the image recipe or at the
	distro configuration level.

	- staticdev-pkgs: Installs static development packages, which are
	static libraries (i.e. ``*.a`` files), for all packages installed in
	a given image.

	Some image features are available only when you inherit the
	:ref:`core-image <ref-classes-core-image>` class. The current list of
	these valid features is as follows:

	- hwcodecs: Installs hardware acceleration codecs.

	- nfs-server: Installs an NFS server.

	- perf: Installs profiling tools such as ``perf``, ``systemtap``, and
	``LTTng``. For general information on user-space tools, see the
	:doc:`/sdk-manual/index` manual.

	- ssh-server-dropbear: Installs the Dropbear minimal SSH server.

	- ssh-server-openssh: Installs the OpenSSH SSH server, which is more
	full-featured than Dropbear. Note that if both the OpenSSH SSH server
	and the Dropbear minimal SSH server are present in
	``IMAGE_FEATURES``, then OpenSSH will take precedence and Dropbear
	will not be installed.

	- tools-debug: Installs debugging tools such as ``strace`` and
	``gdb``. For information on GDB, see the
	":ref:`dev-manual/common-tasks:debugging with the gnu project debugger (gdb) remotely`" section
	in the Yocto Project Development Tasks Manual. For information on
	tracing and profiling, see the :doc:`/profile-manual/index`.

	- tools-sdk: Installs a full SDK that runs on the device.

	- tools-testapps: Installs device testing tools (e.g. touchscreen
	debugging).

	- x11: Installs the X server.

	- x11-base: Installs the X server with a minimal environment.

	- x11-sato: Installs the OpenedHand Sato environment.

	.. _ref-features-backfill:

	Feature Backfilling
	===================

	Sometimes it is necessary in the OpenEmbedded build system to extend
	:term:`MACHINE_FEATURES` or
	:term:`DISTRO_FEATURES` to control functionality
	that was previously enabled and not able to be disabled. For these
	cases, we need to add an additional feature item to appear in one of
	these variables, but we do not want to force developers who have
	existing values of the variables in their configuration to add the new
	feature in order to retain the same overall level of functionality.
	Thus, the OpenEmbedded build system has a mechanism to automatically
	"backfill" these added features into existing distro or machine
	configurations. You can see the list of features for which this is done
	by finding the
	:term:`DISTRO_FEATURES_BACKFILL` and
	:term:`MACHINE_FEATURES_BACKFILL`
	variables in the ``meta/conf/bitbake.conf`` file.

	Because such features are backfilled by default into all configurations
	as described in the previous paragraph, developers who wish to disable
	the new features need to be able to selectively prevent the backfilling
	from occurring. They can do this by adding the undesired feature or
	features to the
	:term:`DISTRO_FEATURES_BACKFILL_CONSIDERED`
	or
	:term:`MACHINE_FEATURES_BACKFILL_CONSIDERED`
	variables for distro features and machine features respectively.

	Here are two examples to help illustrate feature backfilling:

	- The "pulseaudio" distro feature option: Previously, PulseAudio
	support was enabled within the Qt and GStreamer frameworks. Because
	of this, the feature is backfilled and thus enabled for all distros
	through the ``DISTRO_FEATURES_BACKFILL`` variable in the
	``meta/conf/bitbake.conf`` file. However, your distro needs to
	disable the feature. You can disable the feature without affecting
	other existing distro configurations that need PulseAudio support by
	adding "pulseaudio" to ``DISTRO_FEATURES_BACKFILL_CONSIDERED`` in
	your distro's ``.conf`` file. Adding the feature to this variable
	when it also exists in the ``DISTRO_FEATURES_BACKFILL`` variable
	prevents the build system from adding the feature to your
	configuration's ``DISTRO_FEATURES``, effectively disabling the
	feature for that particular distro.

	- The "rtc" machine feature option: Previously, real time clock (RTC)
	support was enabled for all target devices. Because of this, the
	feature is backfilled and thus enabled for all machines through the
	``MACHINE_FEATURES_BACKFILL`` variable in the
	``meta/conf/bitbake.conf`` file. However, your target device does not
	have this capability. You can disable RTC support for your device
	without affecting other machines that need RTC support by adding the
	feature to your machine's ``MACHINE_FEATURES_BACKFILL_CONSIDERED``
	list in the machine's ``.conf`` file. Adding the feature to this
	variable when it also exists in the ``MACHINE_FEATURES_BACKFILL``
	variable prevents the build system from adding the feature to your
	configuration's ``MACHINE_FEATURES``, effectively disabling RTC
	support for that particular machine.