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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
<chapter id='ref-features'>
<title>Reference: Features</title>
<para>
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
<filename><link linkend='var-DISTRO_FEATURES'>DISTRO_FEATURES</link></filename>
variable, which is set in the <filename>poky.conf</filename> distribution configuration file.
Machine features are set in the
<filename><link linkend='var-MACHINE_FEATURES'>MACHINE_FEATURES</link></filename>
variable, which is set in the machine configuration file and
specifies the hardware features for a given machine.
</para>
<para>
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.
</para>
<section id='ref-features-distro'>
<title>Distro</title>
<para>
The items below are valid options for
<filename><link linkend='var-DISTRO_FEATURES'>DISTRO_FEATURES</link></filename>:
<itemizedlist>
<listitem><para><emphasis>alsa:</emphasis> ALSA support will be included (OSS compatibility
kernel modules will be installed if available).</para></listitem>
<listitem><para><emphasis>bluetooth:</emphasis> Include bluetooth support (integrated BT only)
</para></listitem>
<listitem><para><emphasis>ext2:</emphasis> Include tools for supporting for devices with internal
HDD/Microdrive for storing files (instead of Flash only devices)
</para></listitem>
<listitem><para><emphasis>irda:</emphasis> Include Irda support
</para></listitem>
<listitem><para><emphasis>keyboard:</emphasis> Include keyboard support (e.g. keymaps will be
loaded during boot).
</para></listitem>
<listitem><para><emphasis>pci:</emphasis> Include PCI bus support
</para></listitem>
<listitem><para><emphasis>pcmcia:</emphasis> Include PCMCIA/CompactFlash support
</para></listitem>
<listitem><para><emphasis>usbgadget:</emphasis> USB Gadget Device support (for USB
networking/serial/storage)
</para></listitem>
<listitem><para><emphasis>usbhost:</emphasis> USB Host support (allows to connect external
keyboard, mouse, storage, network etc)
</para></listitem>
<listitem><para><emphasis>wifi:</emphasis> WiFi support (integrated only)
</para></listitem>
<listitem><para><emphasis>cramfs:</emphasis> CramFS support
</para></listitem>
<listitem><para><emphasis>ipsec:</emphasis> IPSec support
</para></listitem>
<listitem><para><emphasis>ipv6:</emphasis> IPv6 support
</para></listitem>
<listitem><para><emphasis>nfs:</emphasis> NFS client support (for mounting NFS exports on
device)</para></listitem>
<listitem><para><emphasis>ppp:</emphasis> PPP dialup support</para></listitem>
<listitem><para><emphasis>smbfs:</emphasis> SMB networks client support (for mounting
Samba/Microsoft Windows shares on device)</para></listitem>
</itemizedlist>
</para>
</section>
<section id='ref-features-machine'>
<title>Machine</title>
<para>
The items below are valid options for
<filename><link linkend='var-MACHINE_FEATURES'>MACHINE_FEATURES</link></filename>:
<itemizedlist>
<listitem><para><emphasis>acpi:</emphasis> Hardware has ACPI (x86/x86_64 only)
</para></listitem>
<listitem><para><emphasis>alsa:</emphasis> Hardware has ALSA audio drivers
</para></listitem>
<listitem><para><emphasis>apm:</emphasis> Hardware uses APM (or APM emulation)
</para></listitem>
<listitem><para><emphasis>bluetooth:</emphasis> Hardware has integrated BT
</para></listitem>
<listitem><para><emphasis>ext2:</emphasis> Hardware HDD or Microdrive
</para></listitem>
<listitem><para><emphasis>irda:</emphasis> Hardware has Irda support
</para></listitem>
<listitem><para><emphasis>keyboard:</emphasis> Hardware has a keyboard
</para></listitem>
<listitem><para><emphasis>pci:</emphasis> Hardware has a PCI bus
</para></listitem>
<listitem><para><emphasis>pcmcia:</emphasis> Hardware has PCMCIA or CompactFlash sockets
</para></listitem>
<listitem><para><emphasis>screen:</emphasis> Hardware has a screen
</para></listitem>
<listitem><para><emphasis>serial:</emphasis> Hardware has serial support (usually RS232)
</para></listitem>
<listitem><para><emphasis>touchscreen:</emphasis> Hardware has a touchscreen
</para></listitem>
<listitem><para><emphasis>usbgadget:</emphasis> Hardware is USB gadget device capable
</para></listitem>
<listitem><para><emphasis>usbhost:</emphasis> Hardware is USB Host capable
</para></listitem>
<listitem><para><emphasis>wifi:</emphasis> Hardware has integrated WiFi
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='ref-features-image'>
<title>Images</title>
<para>
The contents of images generated by the OpenEmbedded build system can be controlled by the
<filename><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></filename>
and <filename><link linkend='var-EXTRA_IMAGE_FEATURES'>EXTRA_IMAGE_FEATURES</link></filename>
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.
</para>
<para>
Current list of
<filename>IMAGE_FEATURES</filename> contains the following:
<itemizedlist>
<listitem><para><emphasis>splash:</emphasis> Enables showing a splash screen during boot.
By default, this screen is provided by <filename>psplash</filename>, which does
allow customization.
If you prefer to use an alternative splash screen package, you can do so by
setting the <filename>SPLASH</filename> variable
to a different package name (or names) within the image recipe or at the distro
configuration level.</para></listitem>
<listitem><para><emphasis>ssh-server-dropbear:</emphasis> Installs the Dropbear minimal
SSH server.
</para></listitem>
<listitem><para><emphasis>ssh-server-openssh:</emphasis> 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 <filename>IMAGE_FEATURES</filename>, then OpenSSH will take
precedence and Dropbear will not be installed.</para></listitem>
<listitem><para><emphasis>x11:</emphasis> Installs the X server</para></listitem>
<listitem><para><emphasis>x11-base:</emphasis> Installs the X server with a
minimal environment.</para></listitem>
<listitem><para><emphasis>x11-sato:</emphasis> Installs the OpenedHand Sato environment.
</para></listitem>
<listitem><para><emphasis>tools-sdk:</emphasis> Installs a full SDK that runs on the device.
</para></listitem>
<listitem><para><emphasis>tools-debug:</emphasis> Installs debugging tools such as
<filename>strace</filename> and <filename>gdb</filename>.
</para></listitem>
<listitem><para><emphasis>tools-profile:</emphasis> Installs profiling tools such as
<filename>oprofile</filename>, <filename>exmap</filename>, and
<filename>LTTng</filename>.</para></listitem>
<listitem><para><emphasis>tools-testapps:</emphasis> Installs device testing tools (e.g.
touchscreen debugging).</para></listitem>
<listitem><para><emphasis>nfs-server:</emphasis> Installs an NFS server.</para></listitem>
<listitem><para><emphasis>dev-pkgs:</emphasis> Installs development packages (headers and
extra library links) for all packages installed in a given image.</para></listitem>
<listitem><para><emphasis>staticdev-pkgs:</emphasis> Installs static development
packages (i.e. static libraries containing <filename>*.a</filename> files) for all
packages installed in a given image.</para></listitem>
<listitem><para><emphasis>dbg-pkgs:</emphasis> Installs debug symbol packages for all packages
installed in a given image.</para></listitem>
<listitem><para><emphasis>doc-pkgs:</emphasis> Installs documentation packages for all packages
installed in a given image.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='ref-features-backfill'>
<title>Feature Backfilling</title>
<para>
Sometimes, it is necessary for a new feature to be added to control existing
functionality that was previously enabled by default and not able to be disabled.
In order to ensure that the feature remains enabled for users with existing
configurations that upgrade to a new version of the core metadata without that
configuration having to be changed, while still allowing others who want to turn
the feature off to do so, the backfilling mechanism was introduced.
This
functionality is available for <filename><link linkend='var-DISTRO_FEATURES'>DISTRO_FEATURES</link></filename>
and <filename><link linkend='var-MACHINE_FEATURES'>MACHINE_FEATURES</link></filename>.
</para>
<para>
An example is the "pulseaudio" distro feature.
Previously, PulseAudio support
was enabled within the Qt and GStreamer frameworks.
However some users desired
to be able to disable this.
To allow this to be disabled without affecting
existing configurations in which PulseAudio support should remain enabled,
"pulseaudio" was added to
<filename><link linkend='var-DISTRO_FEATURES_BACKFILL'>DISTRO_FEATURES_BACKFILL</link></filename>
within <filename>meta/conf/bitbake.conf</filename>.
This means that "pulseaudio"
is automatically added to <filename>DISTRO_FEATURES</filename> without the distro
configuration needing to be updated to do so itself.
Those who do not want PulseAudio support can add "pulseaudio" to
<filename><link linkend='var-DISTRO_FEATURES_BACKFILL_CONSIDERED'>DISTRO_FEATURES_BACKFILL_CONSIDERED</link></filename>
in their distro <filename>.conf</filename> file and this will disable adding "pulseaudio" to
<filename>DISTRO_FEATURES</filename>.
</para>
<para>
Another example is the "rtc" machine feature.
Previously, real time clock (RTC)
support was enabled for all target devices.
However certain targets do not have
this capability.
To allow this to be disabled by such machines without affecting
other machines in which RTC support should remain enabled, "rtc" was added to
<filename><link linkend='var-MACHINE_FEATURES_BACKFILL'>MACHINE_FEATURES_BACKFILL</link></filename>
within <filename>meta/conf/bitbake.conf</filename>.
This means that "rtc"
is automatically added to <filename>MACHINE_FEATURES</filename> without the
machine configuration needing to be updated to do so itself.
For machines that not need RTC support can add "rtc" to
<filename><link linkend='var-MACHINE_FEATURES_BACKFILL_CONSIDERED'>MACHINE_FEATURES_BACKFILL_CONSIDERED</link></filename>
in their machine <filename>.conf</filename> file and this will disable adding "rtc" to
<filename>MACHINE_FEATURES</filename>.
</para>
</section>
</chapter>
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