329 lines
19 KiB
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329 lines
19 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='ref-features'>
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<title>Reference: Features</title>
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<para>
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This chapter provides a reference of shipped machine and distro features
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you can include as part of the image, a reference on image types you can
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build, and a reference on feature backfilling.
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</para>
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<para>
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Features provide a mechanism for working out which packages
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should be included in the generated images.
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Distributions can select which features they want to support through the
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<filename><link linkend='var-DISTRO_FEATURES'>DISTRO_FEATURES</link></filename>
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variable, which is set in the <filename>poky.conf</filename> distribution configuration file.
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Machine features are set in the
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<filename><link linkend='var-MACHINE_FEATURES'>MACHINE_FEATURES</link></filename>
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variable, which is set in the machine configuration file and
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specifies the hardware features for a given machine.
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</para>
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<para>
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These two variables combine to work out which kernel modules,
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utilities, and other packages to include.
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A given distribution can support a selected subset of features so some machine features might not
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be included if the distribution itself does not support them.
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</para>
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<para>
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One method you can use to determine which recipes are checking to see if a
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particular feature is contained or not is to <filename>grep</filename> through
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the <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
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for the feature.
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Here is an example that discovers the recipes whose build is potentially
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changed based on a given feature:
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<literallayout class='monospaced'>
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$ cd $HOME/poky
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$ git grep 'contains.*MACHINE_FEATURES.*<feature>'
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</literallayout>
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</para>
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<section id='ref-features-distro'>
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<title>Distro</title>
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<para>
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The items below are features you can use with
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<link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>.
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Features do not have a one-to-one correspondence to packages, and they can
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go beyond simply controlling the installation of a package or packages.
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Sometimes a feature can influence how certain recipes are built.
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For example, a feature might determine whether a particular configure option
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is specified within <filename>do_configure</filename> for a particular
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recipe.
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</para>
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<para>
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This list only represents features as shipped with the Yocto Project metadata:
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<itemizedlist>
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<listitem><para><emphasis>alsa:</emphasis> Include ALSA support
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(OSS compatibility kernel modules installed if available).
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</para></listitem>
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<listitem><para><emphasis>bluetooth:</emphasis> Include
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bluetooth support (integrated BT only).</para></listitem>
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<listitem><para><emphasis>cramfs:</emphasis> Include CramFS
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support.</para></listitem>
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<listitem><para><emphasis>ext2:</emphasis> Include tools for
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supporting for devices with internal HDD/Microdrive for
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storing files (instead of Flash only devices).
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</para></listitem>
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<listitem><para><emphasis>ipsec:</emphasis> Include IPSec
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support.</para></listitem>
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<listitem><para><emphasis>ipv6:</emphasis> Include IPv6 support.
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</para></listitem>
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<listitem><para><emphasis>irda:</emphasis> Include Irda support.
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</para></listitem>
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<listitem><para><emphasis>keyboard:</emphasis> Include keyboard
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support (e.g. keymaps will be loaded during boot).
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</para></listitem>
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<listitem><para><emphasis>nfs:</emphasis> Include NFS client
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support (for mounting NFS exports on device).
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</para></listitem>
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<listitem><para><emphasis>opengl:</emphasis>
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Include the Open Graphics Library, which is a
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cross-language, multi-platform application programming
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interface used for rendering two and three-dimensional
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graphics.</para></listitem>
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<listitem><para><emphasis>pci:</emphasis> Include PCI bus
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support.</para></listitem>
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<listitem><para><emphasis>pcmcia:</emphasis> Include
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PCMCIA/CompactFlash support.</para></listitem>
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<listitem><para><emphasis>ppp:</emphasis> Include PPP dialup
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support.</para></listitem>
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<listitem><para><emphasis>smbfs:</emphasis> Include SMB networks
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client support (for mounting Samba/Microsoft Windows shares
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on device).</para></listitem>
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<listitem><para><emphasis>systemd:</emphasis> Include support
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for this <filename>init</filename> manager, which is a full
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replacement of for <filename>init</filename> with parallel
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starting of services, reduced shell overhead, and other
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features.
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This <filename>init</filename> manager is used by many
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distributions.</para></listitem>
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<listitem><para><emphasis>usbgadget:</emphasis> Include USB
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Gadget Device support (for USB networking/serial/storage).
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</para></listitem>
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<listitem><para><emphasis>usbhost:</emphasis> Include USB Host
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support (allows to connect external keyboard, mouse,
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storage, network etc).</para></listitem>
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<listitem><para><emphasis>wayland:</emphasis> Include the
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Wayland display server protocol and the library that
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supports it.</para></listitem>
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<listitem><para><emphasis>wifi:</emphasis> Include WiFi support
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(integrated only).</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='ref-features-machine'>
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<title>Machine</title>
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<para>
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The items below are features you can use with
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<link linkend='var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></link>.
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Features do not have a one-to-one correspondence to packages, and they can
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go beyond simply controlling the installation of a package or packages.
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Sometimes a feature can influence how certain recipes are built.
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For example, a feature might determine whether a particular configure option
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is specified within <filename>do_configure</filename> for a particular
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recipe.
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</para>
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<para>
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This feature list only represents features as shipped with the Yocto Project metadata:
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<itemizedlist>
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<listitem><para><emphasis>acpi:</emphasis> Hardware has ACPI (x86/x86_64 only)
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</para></listitem>
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<listitem><para><emphasis>alsa:</emphasis> Hardware has ALSA audio drivers
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</para></listitem>
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<listitem><para><emphasis>apm:</emphasis> Hardware uses APM (or APM emulation)
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</para></listitem>
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<listitem><para><emphasis>bluetooth:</emphasis> Hardware has integrated BT
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</para></listitem>
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<listitem><para><emphasis>ext2:</emphasis> Hardware HDD or Microdrive
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</para></listitem>
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<listitem><para><emphasis>irda:</emphasis> Hardware has Irda support
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</para></listitem>
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<listitem><para><emphasis>keyboard:</emphasis> Hardware has a keyboard
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</para></listitem>
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<listitem><para><emphasis>pci:</emphasis> Hardware has a PCI bus
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</para></listitem>
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<listitem><para><emphasis>pcmcia:</emphasis> Hardware has PCMCIA or CompactFlash sockets
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</para></listitem>
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<listitem><para><emphasis>screen:</emphasis> Hardware has a screen
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</para></listitem>
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<listitem><para><emphasis>serial:</emphasis> Hardware has serial support (usually RS232)
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</para></listitem>
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<listitem><para><emphasis>touchscreen:</emphasis> Hardware has a touchscreen
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</para></listitem>
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<listitem><para><emphasis>usbgadget:</emphasis> Hardware is USB gadget device capable
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</para></listitem>
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<listitem><para><emphasis>usbhost:</emphasis> Hardware is USB Host capable
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</para></listitem>
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<listitem><para><emphasis>wifi:</emphasis> Hardware has integrated WiFi
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</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='ref-features-image'>
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<title>Images</title>
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<para>
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The contents of images generated by the OpenEmbedded build system can be controlled by the
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<filename><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></filename>
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and <filename><link linkend='var-EXTRA_IMAGE_FEATURES'>EXTRA_IMAGE_FEATURES</link></filename>
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variables that you typically configure in your image recipes.
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Through these variables, you can add several different
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predefined packages such as development utilities or packages with debug
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information needed to investigate application problems or profile applications.
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</para>
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<para>
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Current list of
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<filename>IMAGE_FEATURES</filename> contains the following:
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<itemizedlist>
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<listitem><para><emphasis>dbg-pkgs:</emphasis> Installs debug symbol packages for all packages
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installed in a given image.</para></listitem>
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<listitem><para><emphasis>dev-pkgs:</emphasis> Installs development packages (headers and
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extra library links) for all packages installed in a given image.</para></listitem>
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<listitem><para><emphasis>doc-pkgs:</emphasis> Installs documentation packages for all packages
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installed in a given image.</para></listitem>
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<listitem><para><emphasis>nfs-server:</emphasis> Installs an NFS server.</para></listitem>
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<listitem><para><emphasis>read-only-rootfs:</emphasis> Creates
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an image whose root filesystem is read-only.
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See the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-read-only-root-filesystem'>Creating a Read-Only Root Filesystem</ulink>"
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section in the Yocto Project Development Manual for more
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information.</para></listitem>
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<listitem><para><emphasis>splash:</emphasis> Enables showing a splash screen during boot.
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By default, this screen is provided by <filename>psplash</filename>, which does
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allow customization.
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If you prefer to use an alternative splash screen package, you can do so by
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setting the <filename>SPLASH</filename> variable
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to a different package name (or names) within the image recipe or at the distro
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configuration level.</para></listitem>
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<listitem><para><emphasis>ssh-server-dropbear:</emphasis> Installs the Dropbear minimal
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SSH server.
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</para></listitem>
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<listitem><para><emphasis>ssh-server-openssh:</emphasis> Installs the OpenSSH SSH server,
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which is more full-featured than Dropbear.
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Note that if both the OpenSSH SSH server and the Dropbear minimal SSH server
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are present in <filename>IMAGE_FEATURES</filename>, then OpenSSH will take
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precedence and Dropbear will not be installed.</para></listitem>
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<listitem><para><emphasis>staticdev-pkgs:</emphasis> Installs static development
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packages (i.e. static libraries containing <filename>*.a</filename> files) for all
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packages installed in a given image.</para></listitem>
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<listitem><para><emphasis>tools-debug:</emphasis> Installs debugging tools such as
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<filename>strace</filename> and <filename>gdb</filename>.
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For information on GDB, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#platdev-gdb-remotedebug'>Debugging With the GNU Project Debugger (GDB) Remotely</ulink>"
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section in the Yocto Project Development Manual.
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For information on tracing and profiling, see the
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<ulink url='&YOCTO_DOCS_PROF_URL;'>Yocto Project Profiling and Tracing Manual</ulink>.
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</para></listitem>
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<listitem><para><emphasis>tools-profile:</emphasis> Installs profiling tools such as
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<filename>oprofile</filename>, <filename>exmap</filename>, and
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<filename>LTTng</filename>.
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For general information on user-space tools, see the
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"<ulink url='&YOCTO_DOCS_ADT_URL;#user-space-tools'>User-Space Tools</ulink>"
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section in the Yocto Project Application Developer's Guide.</para></listitem>
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<listitem><para><emphasis>tools-sdk:</emphasis> Installs a full SDK that runs on the device.
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</para></listitem>
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<listitem><para><emphasis>tools-testapps:</emphasis> Installs device testing tools (e.g.
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touchscreen debugging).</para></listitem>
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<listitem><para><emphasis>x11:</emphasis> Installs the X server</para></listitem>
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<listitem><para><emphasis>x11-base:</emphasis> Installs the X server with a
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minimal environment.</para></listitem>
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<listitem><para><emphasis>x11-sato:</emphasis> Installs the OpenedHand Sato environment.
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</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='ref-features-backfill'>
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<title>Feature Backfilling</title>
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<para>
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Sometimes it is necessary in the OpenEmbedded build system to extend
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<link linkend='var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></link>
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or <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>
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to control functionality that was previously enabled and not able
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to be disabled.
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For these cases, we need to add an
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additional feature item to appear in one of these variables,
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but we do not want to force developers who have existing values
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of the variables in their configuration to add the new feature
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in order to retain the same overall level of functionality.
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Thus, the OpenEmbedded build system has a mechanism to
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automatically "backfill" these added features into existing
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distro or machine configurations.
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You can see the list of features for which this is done by
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finding the
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<link linkend='var-DISTRO_FEATURES_BACKFILL'><filename>DISTRO_FEATURES_BACKFILL</filename></link>
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and <link linkend='var-MACHINE_FEATURES_BACKFILL'><filename>MACHINE_FEATURES_BACKFILL</filename></link>
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variables in the <filename>meta/conf/bitbake.conf</filename> file.
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</para>
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<para>
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Because such features are backfilled by default into all
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configurations as described in the previous paragraph, developers
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who wish to disable the new features need to be able to selectively
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prevent the backfilling from occurring.
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They can do this by adding the undesired feature or features to the
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<link linkend='var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></link>
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or <link linkend='var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></link>
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variables for distro features and machine features respectively.
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</para>
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<para>
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Here are two examples to help illustrate feature backfilling:
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<itemizedlist>
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<listitem><para><emphasis>The "pulseaudio" distro feature option</emphasis>:
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Previously, PulseAudio support was enabled within the Qt and
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GStreamer frameworks.
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Because of this, the feature is backfilled and thus
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enabled for all distros through the
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<filename>DISTRO_FEATURES_BACKFILL</filename>
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variable in the <filename>meta/conf/bitbake.conf</filename> file.
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However, your distro needs to disable the feature.
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You can disable the feature without affecting
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other existing distro configurations that need PulseAudio support
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by adding "pulseaudio" to
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<filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename>
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in your distro's <filename>.conf</filename> file.
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Adding the feature to this variable when it also
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exists in the <filename>DISTRO_FEATURES_BACKFILL</filename>
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variable prevents the build system from adding the feature to
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your configuration's <filename>DISTRO_FEATURES</filename>, effectively disabling
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the feature for that particular distro.</para></listitem>
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<listitem><para><emphasis>The "rtc" machine feature option</emphasis>:
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Previously, real time clock (RTC) support was enabled for all
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target devices.
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Because of this, the feature is backfilled and thus enabled
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for all machines through the <filename>MACHINE_FEATURES_BACKFILL</filename>
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variable in the <filename>meta/conf/bitbake.conf</filename> file.
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However, your target device does not have this capability.
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You can disable RTC support for your device without
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affecting other machines that need RTC support
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by adding the feature to your machine's
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<filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename>
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list in the machine's <filename>.conf</filename> file.
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Adding the feature to this variable when it also
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exists in the <filename>MACHINE_FEATURES_BACKFILL</filename>
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variable prevents the build system from adding the feature to
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your configuration's <filename>MACHINE_FEATURES</filename>, effectively
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disabling RTC support for that particular machine.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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</chapter>
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<!--
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vim: expandtab tw=80 ts=4 spell spelllang=en_gb
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-->
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