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Andrew Geisslerf0343792020-11-18 10:42:21 -06001.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
Andrew Geisslerc9f78652020-09-18 14:11:35 -05002
3********
4Features
5********
6
7This chapter provides a reference of shipped machine and distro features
8you can include as part of your image, a reference on image features you
9can select, and a reference on feature backfilling.
10
11Features provide a mechanism for working out which packages should be
12included in the generated images. Distributions can select which
Andrew Geissler09036742021-06-25 14:25:14 -050013features they want to support through the :term:`DISTRO_FEATURES` variable,
Andrew Geisslerc9f78652020-09-18 14:11:35 -050014which is set or appended to in a distribution's configuration file such
15as ``poky.conf``, ``poky-tiny.conf``, ``poky-lsb.conf`` and so forth.
Andrew Geissler09036742021-06-25 14:25:14 -050016Machine features are set in the :term:`MACHINE_FEATURES` variable, which is
Andrew Geisslerc9f78652020-09-18 14:11:35 -050017set in the machine configuration file and specifies the hardware
18features for a given machine.
19
20These two variables combine to work out which kernel modules, utilities,
21and other packages to include. A given distribution can support a
22selected subset of features so some machine features might not be
23included if the distribution itself does not support them.
24
25One method you can use to determine which recipes are checking to see if
26a particular feature is contained or not is to ``grep`` through the
27:term:`Metadata` for the feature. Here is an example that
28discovers the recipes whose build is potentially changed based on a
Andrew Geisslerc926e172021-05-07 16:11:35 -050029given feature::
Andrew Geisslerc9f78652020-09-18 14:11:35 -050030
31 $ cd poky
32 $ git grep 'contains.*MACHINE_FEATURES.*feature'
33
34.. _ref-features-machine:
35
36Machine Features
37================
38
39The items below are features you can use with
40:term:`MACHINE_FEATURES`. Features do not have a
41one-to-one correspondence to packages, and they can go beyond simply
42controlling the installation of a package or packages. Sometimes a
43feature can influence how certain recipes are built. For example, a
44feature might determine whether a particular configure option is
45specified within the :ref:`ref-tasks-configure` task
46for a particular recipe.
47
48This feature list only represents features as shipped with the Yocto
49Project metadata:
50
51- *acpi:* Hardware has ACPI (x86/x86_64 only)
52
53- *alsa:* Hardware has ALSA audio drivers
54
55- *apm:* Hardware uses APM (or APM emulation)
56
57- *bluetooth:* Hardware has integrated BT
58
59- *efi:* Support for booting through EFI
60
61- *ext2:* Hardware HDD or Microdrive
62
63- *keyboard:* Hardware has a keyboard
64
Patrick Williams92b42cb2022-09-03 06:53:57 -050065- *numa:* Hardware has non-uniform memory access
66
Andrew Geisslerc9f78652020-09-18 14:11:35 -050067- *pcbios:* Support for booting through BIOS
68
69- *pci:* Hardware has a PCI bus
70
71- *pcmcia:* Hardware has PCMCIA or CompactFlash sockets
72
73- *phone:* Mobile phone (voice) support
74
Patrick Williams975a06f2022-10-21 14:42:47 -050075- *qemu-usermode:* QEMU can support user-mode emulation for this machine
76
Andrew Geisslerc9f78652020-09-18 14:11:35 -050077- *qvga:* Machine has a QVGA (320x240) display
78
79- *rtc:* Machine has a Real-Time Clock
80
81- *screen:* Hardware has a screen
82
83- *serial:* Hardware has serial support (usually RS232)
84
85- *touchscreen:* Hardware has a touchscreen
86
87- *usbgadget:* Hardware is USB gadget device capable
88
89- *usbhost:* Hardware is USB Host capable
90
91- *vfat:* FAT file system support
92
93- *wifi:* Hardware has integrated WiFi
94
95.. _ref-features-distro:
96
97Distro Features
98===============
99
100The items below are features you can use with
101:term:`DISTRO_FEATURES` to enable features across
102your distribution. Features do not have a one-to-one correspondence to
103packages, and they can go beyond simply controlling the installation of
104a package or packages. In most cases, the presence or absence of a
105feature translates to the appropriate option supplied to the configure
106script during the :ref:`ref-tasks-configure` task for
Andrew Geissler615f2f12022-07-15 14:00:58 -0500107the recipes that optionally support the feature. Appropriate options
108must be supplied, and enabling/disabling :term:`PACKAGECONFIG` for the
109concerned packages is one way of supplying such options.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500110
111Some distro features are also machine features. These select features
112make sense to be controlled both at the machine and distribution
113configuration level. See the
114:term:`COMBINED_FEATURES` variable for more
115information.
116
Patrick Williams975a06f2022-10-21 14:42:47 -0500117.. note::
118
119 :term:`DISTRO_FEATURES` is normally independent of kernel configuration,
120 so if a feature specified in :term:`DISTRO_FEATURES` also relies on
121 support in the kernel, you will also need to ensure that support is
122 enabled in the kernel configuration.
123
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500124This list only represents features as shipped with the Yocto Project
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500125metadata, as extra layers can define their own:
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500126
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500127- *3g:* Include support for cellular data.
128
Patrick Williams7784c422022-11-17 07:29:11 -0600129- *acl:* Include :wikipedia:`Access Control List <Access-control_list>` support.
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500130
Patrick Williams7784c422022-11-17 07:29:11 -0600131- *alsa:* Include :wikipedia:`Advanced Linux Sound Architecture <Advanced_Linux_Sound_Architecture>`
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500132 support (OSS compatibility kernel modules installed if available).
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500133
134- *api-documentation:* Enables generation of API documentation during
135 recipe builds. The resulting documentation is added to SDK tarballs
136 when the ``bitbake -c populate_sdk`` command is used. See the
Andrew Geissler09209ee2020-12-13 08:44:15 -0600137 ":ref:`sdk-manual/appendix-customizing-standard:adding api documentation to the standard sdk`"
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500138 section in the Yocto Project Application Development and the
139 Extensible Software Development Kit (eSDK) manual.
140
141- *bluetooth:* Include bluetooth support (integrated BT only).
142
143- *cramfs:* Include CramFS support.
144
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500145- *debuginfod:* Include support for getting ELF debugging information through
Andrew Geissler517393d2023-01-13 08:55:19 -0600146 a :ref:`debuginfod <dev-manual/debugging:using the debuginfod server method>`
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500147 server.
148
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500149- *directfb:* Include DirectFB support.
150
151- *ext2:* Include tools for supporting for devices with internal
152 HDD/Microdrive for storing files (instead of Flash only devices).
153
Patrick Williams975a06f2022-10-21 14:42:47 -0500154- *gobject-introspection-data:* Include data to support
155 `GObject Introspection <https://gi.readthedocs.io/en/latest/>`__.
156
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500157- *ipsec:* Include IPSec support.
158
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500159- *ipv4:* Include IPv4 support.
160
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500161- *ipv6:* Include IPv6 support.
162
163- *keyboard:* Include keyboard support (e.g. keymaps will be loaded
164 during boot).
165
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500166- *multiarch:* Enable building applications with multiple architecture
167 support.
168
Patrick Williams7784c422022-11-17 07:29:11 -0600169- *ld-is-gold:* Use the :wikipedia:`gold <Gold_(linker)>`
Patrick Williams975a06f2022-10-21 14:42:47 -0500170 linker instead of the standard GCC linker (bfd).
171
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500172- *ldconfig:* Include support for ldconfig and ``ld.so.conf`` on the
173 target.
174
Patrick Williams975a06f2022-10-21 14:42:47 -0500175- *lto:* Enable `Link-Time Optimisation <https://gcc.gnu.org/wiki/LinkTimeOptimization>`__.
176
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500177- *nfc:* Include support for
178 `Near Field Communication <https://en.wikipedia.org/wiki/Near-field_communication>`__.
179
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500180- *nfs:* Include NFS client support (for mounting NFS exports on
181 device).
182
Patrick Williams975a06f2022-10-21 14:42:47 -0500183- *nls:* Include National Language Support (NLS).
184
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500185- *opengl:* Include the Open Graphics Library, which is a
186 cross-language, multi-platform application programming interface used
187 for rendering two and three-dimensional graphics.
188
Patrick Williams975a06f2022-10-21 14:42:47 -0500189- *overlayfs:* Include `OverlayFS <https://docs.kernel.org/filesystems/overlayfs.html>`__
190 support.
191
Patrick Williams7784c422022-11-17 07:29:11 -0600192- *pam:* Include :wikipedia:`Pluggable Authentication Module (PAM) <Pluggable_authentication_module>`
Patrick Williams975a06f2022-10-21 14:42:47 -0500193 support.
194
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500195- *pci:* Include PCI bus support.
196
197- *pcmcia:* Include PCMCIA/CompactFlash support.
198
Patrick Williams7784c422022-11-17 07:29:11 -0600199- *polkit:* Include :wikipedia:`Polkit <Polkit>` support.
Patrick Williams975a06f2022-10-21 14:42:47 -0500200
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500201- *ppp:* Include PPP dialup support.
202
203- *ptest:* Enables building the package tests where supported by
204 individual recipes. For more information on package tests, see the
Andrew Geissler517393d2023-01-13 08:55:19 -0600205 ":ref:`dev-manual/packages:testing packages with ptest`" section
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500206 in the Yocto Project Development Tasks Manual.
207
Patrick Williams975a06f2022-10-21 14:42:47 -0500208- *pulseaudio:* Include support for
209 `PulseAudio <https://www.freedesktop.org/wiki/Software/PulseAudio/>`__.
210
211- *selinux:* Include support for
Patrick Williams7784c422022-11-17 07:29:11 -0600212 :wikipedia:`Security-Enhanced Linux (SELinux) <Security-Enhanced_Linux>`
Patrick Williams975a06f2022-10-21 14:42:47 -0500213 (requires `meta-selinux <https://layers.openembedded.org/layerindex/layer/meta-selinux/>`__).
214
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500215- *seccomp:* Enables building applications with
Patrick Williams7784c422022-11-17 07:29:11 -0600216 :wikipedia:`seccomp <Seccomp>` support, to
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500217 allow them to strictly restrict the system calls that they are allowed
218 to invoke.
219
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500220- *smbfs:* Include SMB networks client support (for mounting
221 Samba/Microsoft Windows shares on device).
222
223- *systemd:* Include support for this ``init`` manager, which is a full
224 replacement of for ``init`` with parallel starting of services,
225 reduced shell overhead, and other features. This ``init`` manager is
226 used by many distributions.
227
228- *usbgadget:* Include USB Gadget Device support (for USB
229 networking/serial/storage).
230
231- *usbhost:* Include USB Host support (allows to connect external
232 keyboard, mouse, storage, network etc).
233
234- *usrmerge:* Merges the ``/bin``, ``/sbin``, ``/lib``, and ``/lib64``
235 directories into their respective counterparts in the ``/usr``
236 directory to provide better package and application compatibility.
237
Patrick Williams7784c422022-11-17 07:29:11 -0600238- *vfat:* Include :wikipedia:`FAT filesystem <File_Allocation_Table>`
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500239 support.
240
Patrick Williams7784c422022-11-17 07:29:11 -0600241- *vulkan:* Include support for the :wikipedia:`Vulkan API <Vulkan>`.
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500242
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500243- *wayland:* Include the Wayland display server protocol and the
244 library that supports it.
245
246- *wifi:* Include WiFi support (integrated only).
247
248- *x11:* Include the X server and libraries.
249
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500250- *xattr:* Include support for
Patrick Williams7784c422022-11-17 07:29:11 -0600251 :wikipedia:`extended file attributes <Extended_file_attributes>`.
Andrew Geissler87f5cff2022-09-30 13:13:31 -0500252
253- *zeroconf:* Include support for
254 `zero configuration networking <https://en.wikipedia.org/wiki/Zero-configuration_networking>`__.
255
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500256.. _ref-features-image:
257
258Image Features
259==============
260
261The contents of images generated by the OpenEmbedded build system can be
262controlled by the :term:`IMAGE_FEATURES` and
263:term:`EXTRA_IMAGE_FEATURES` variables that
264you typically configure in your image recipes. Through these variables,
265you can add several different predefined packages such as development
266utilities or packages with debug information needed to investigate
267application problems or profile applications.
268
William A. Kennington IIIac69b482021-06-02 12:28:27 -0700269Here are the image features available for all images:
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500270
Andrew Geissler615f2f12022-07-15 14:00:58 -0500271- *allow-empty-password:* Allows Dropbear and OpenSSH to accept
272 logins from accounts having an empty password string.
273
274- *allow-root-login:* Allows Dropbear and OpenSSH to accept root logins.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500275
276- *dbg-pkgs:* Installs debug symbol packages for all packages installed
277 in a given image.
278
279- *debug-tweaks:* Makes an image suitable for development (e.g. allows
Andrew Geissler615f2f12022-07-15 14:00:58 -0500280 root logins, logins without passwords ---including root ones, and enables
281 post-installation logging). See the ``allow-empty-password``,
282 ``allow-root-login``, ``empty-root-password``, and ``post-install-logging``
283 features in this list for additional information.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500284
285- *dev-pkgs:* Installs development packages (headers and extra library
286 links) for all packages installed in a given image.
287
288- *doc-pkgs:* Installs documentation packages for all packages
289 installed in a given image.
290
Andrew Geissler615f2f12022-07-15 14:00:58 -0500291- *empty-root-password:* This feature or ``debug-tweaks`` is required if
292 you want to allow root login with an empty password. If these features
293 are not present in :term:`IMAGE_FEATURES`, a non-empty password is
294 forced in ``/etc/passwd`` and ``/etc/shadow`` if such files exist.
295
296 .. note::
Andrew Geissler6aa7eec2023-03-03 12:41:14 -0600297 ``empty-root-password`` doesn't set an empty root password by itself.
Andrew Geissler615f2f12022-07-15 14:00:58 -0500298 You get an initial empty root password thanks to the
299 :oe_git:`base-passwd </openembedded-core/tree/meta/recipes-core/base-passwd/>`
300 and :oe_git:`shadow </openembedded-core/tree/meta/recipes-extended/shadow/>`
Andrew Geissler6aa7eec2023-03-03 12:41:14 -0600301 recipes, and the presence of ``empty-root-password`` or ``debug-tweaks``
Andrew Geissler615f2f12022-07-15 14:00:58 -0500302 just disables the mechanism which forces an non-empty password for the
303 root user.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500304
Patrick Williams975a06f2022-10-21 14:42:47 -0500305- *lic-pkgs:* Installs license packages for all packages installed in a
306 given image.
307
Andrew Geissler595f6302022-01-24 19:11:47 +0000308- *overlayfs-etc:* Configures the ``/etc`` directory to be in ``overlayfs``.
309 This allows to store device specific information elsewhere, especially
310 if the root filesystem is configured to be read-only.
311
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500312- *package-management:* Installs package management tools and preserves
313 the package manager database.
314
315- *post-install-logging:* Enables logging postinstall script runs to
316 the ``/var/log/postinstall.log`` file on first boot of the image on
317 the target system.
318
319 .. note::
320
Andrew Geissler4c19ea12020-10-27 13:52:24 -0500321 To make the ``/var/log`` directory on the target persistent, use the
322 :term:`VOLATILE_LOG_DIR` variable by setting it to "no".
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500323
324- *ptest-pkgs:* Installs ptest packages for all ptest-enabled recipes.
325
326- *read-only-rootfs:* Creates an image whose root filesystem is
327 read-only. See the
Andrew Geissler517393d2023-01-13 08:55:19 -0600328 ":ref:`dev-manual/read-only-rootfs:creating a read-only root filesystem`"
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500329 section in the Yocto Project Development Tasks Manual for more
330 information.
331
Patrick Williams975a06f2022-10-21 14:42:47 -0500332- *read-only-rootfs-delayed-postinsts:* when specified in conjunction
333 with ``read-only-rootfs``, specifies that post-install scripts are
334 still permitted (this assumes that the root filesystem will be made
335 writeable for the first boot; this feature does not do anything to
336 ensure that - it just disables the check for post-install scripts.)
337
338- *serial-autologin-root:* when specified in conjunction with
339 ``empty-root-password`` will automatically login as root on the
340 serial console. This of course opens up a security hole if the
341 serial console is potentially accessible to an attacker, so use
342 with caution.
343
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500344- *splash:* Enables showing a splash screen during boot. By default,
345 this screen is provided by ``psplash``, which does allow
346 customization. If you prefer to use an alternative splash screen
347 package, you can do so by setting the ``SPLASH`` variable to a
348 different package name (or names) within the image recipe or at the
349 distro configuration level.
350
Patrick Williams975a06f2022-10-21 14:42:47 -0500351- *stateless-rootfs:*: specifies that the image should be created as
352 stateless - when using ``systemd``, ``systemctl-native`` will not
353 be run on the image, leaving the image for population at runtime by
354 systemd.
355
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500356- *staticdev-pkgs:* Installs static development packages, which are
357 static libraries (i.e. ``*.a`` files), for all packages installed in
358 a given image.
359
360Some image features are available only when you inherit the
Andrew Geissler517393d2023-01-13 08:55:19 -0600361:ref:`ref-classes-core-image` class. The current list of
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500362these valid features is as follows:
363
364- *hwcodecs:* Installs hardware acceleration codecs.
365
366- *nfs-server:* Installs an NFS server.
367
368- *perf:* Installs profiling tools such as ``perf``, ``systemtap``, and
369 ``LTTng``. For general information on user-space tools, see the
Andrew Geissler09209ee2020-12-13 08:44:15 -0600370 :doc:`/sdk-manual/index` manual.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500371
372- *ssh-server-dropbear:* Installs the Dropbear minimal SSH server.
373
Patrick Williams975a06f2022-10-21 14:42:47 -0500374 .. note::
375
376 As of the 4.1 release, the ``ssh-server-dropbear`` feature also
377 recommends the ``openssh-sftp-server`` package, which by default
378 will be pulled into the image. This is because recent versions of
379 the OpenSSH ``scp`` client now use the SFTP protocol, and thus
380 require an SFTP server to be present to connect to. However, if
381 you wish to use the Dropbear ssh server `without` the SFTP server
382 installed, you can either remove ``ssh-server-dropbear`` from
383 ``IMAGE_FEATURES`` and add ``dropbear`` to :term:`IMAGE_INSTALL`
384 instead, or alternatively still use the feature but set
385 :term:`BAD_RECOMMENDATIONS` as follows::
386
387 BAD_RECOMMENDATIONS += "openssh-sftp-server"
388
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500389- *ssh-server-openssh:* Installs the OpenSSH SSH server, which is more
390 full-featured than Dropbear. Note that if both the OpenSSH SSH server
391 and the Dropbear minimal SSH server are present in
Andrew Geissler09036742021-06-25 14:25:14 -0500392 :term:`IMAGE_FEATURES`, then OpenSSH will take precedence and Dropbear
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500393 will not be installed.
394
395- *tools-debug:* Installs debugging tools such as ``strace`` and
396 ``gdb``. For information on GDB, see the
Andrew Geissler517393d2023-01-13 08:55:19 -0600397 ":ref:`dev-manual/debugging:debugging with the gnu project debugger (gdb) remotely`" section
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500398 in the Yocto Project Development Tasks Manual. For information on
Andrew Geissler09209ee2020-12-13 08:44:15 -0600399 tracing and profiling, see the :doc:`/profile-manual/index`.
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500400
401- *tools-sdk:* Installs a full SDK that runs on the device.
402
403- *tools-testapps:* Installs device testing tools (e.g. touchscreen
404 debugging).
405
Patrick Williams975a06f2022-10-21 14:42:47 -0500406- *weston:* Installs Weston (reference Wayland environment).
407
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500408- *x11:* Installs the X server.
409
410- *x11-base:* Installs the X server with a minimal environment.
411
412- *x11-sato:* Installs the OpenedHand Sato environment.
413
414.. _ref-features-backfill:
415
416Feature Backfilling
417===================
418
419Sometimes it is necessary in the OpenEmbedded build system to extend
420:term:`MACHINE_FEATURES` or
421:term:`DISTRO_FEATURES` to control functionality
422that was previously enabled and not able to be disabled. For these
423cases, we need to add an additional feature item to appear in one of
424these variables, but we do not want to force developers who have
425existing values of the variables in their configuration to add the new
426feature in order to retain the same overall level of functionality.
427Thus, the OpenEmbedded build system has a mechanism to automatically
428"backfill" these added features into existing distro or machine
429configurations. You can see the list of features for which this is done
430by finding the
431:term:`DISTRO_FEATURES_BACKFILL` and
432:term:`MACHINE_FEATURES_BACKFILL`
433variables in the ``meta/conf/bitbake.conf`` file.
434
435Because such features are backfilled by default into all configurations
436as described in the previous paragraph, developers who wish to disable
437the new features need to be able to selectively prevent the backfilling
438from occurring. They can do this by adding the undesired feature or
439features to the
440:term:`DISTRO_FEATURES_BACKFILL_CONSIDERED`
441or
442:term:`MACHINE_FEATURES_BACKFILL_CONSIDERED`
443variables for distro features and machine features respectively.
444
445Here are two examples to help illustrate feature backfilling:
446
447- *The "pulseaudio" distro feature option*: Previously, PulseAudio
448 support was enabled within the Qt and GStreamer frameworks. Because
449 of this, the feature is backfilled and thus enabled for all distros
Andrew Geissler09036742021-06-25 14:25:14 -0500450 through the :term:`DISTRO_FEATURES_BACKFILL` variable in the
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500451 ``meta/conf/bitbake.conf`` file. However, your distro needs to
452 disable the feature. You can disable the feature without affecting
453 other existing distro configurations that need PulseAudio support by
Andrew Geissler09036742021-06-25 14:25:14 -0500454 adding "pulseaudio" to :term:`DISTRO_FEATURES_BACKFILL_CONSIDERED` in
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500455 your distro's ``.conf`` file. Adding the feature to this variable
Andrew Geissler09036742021-06-25 14:25:14 -0500456 when it also exists in the :term:`DISTRO_FEATURES_BACKFILL` variable
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500457 prevents the build system from adding the feature to your
Andrew Geissler09036742021-06-25 14:25:14 -0500458 configuration's :term:`DISTRO_FEATURES`, effectively disabling the
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500459 feature for that particular distro.
460
461- *The "rtc" machine feature option*: Previously, real time clock (RTC)
462 support was enabled for all target devices. Because of this, the
463 feature is backfilled and thus enabled for all machines through the
Andrew Geissler09036742021-06-25 14:25:14 -0500464 :term:`MACHINE_FEATURES_BACKFILL` variable in the
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500465 ``meta/conf/bitbake.conf`` file. However, your target device does not
466 have this capability. You can disable RTC support for your device
467 without affecting other machines that need RTC support by adding the
Andrew Geissler09036742021-06-25 14:25:14 -0500468 feature to your machine's :term:`MACHINE_FEATURES_BACKFILL_CONSIDERED`
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500469 list in the machine's ``.conf`` file. Adding the feature to this
Andrew Geissler09036742021-06-25 14:25:14 -0500470 variable when it also exists in the :term:`MACHINE_FEATURES_BACKFILL`
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500471 variable prevents the build system from adding the feature to your
Andrew Geissler09036742021-06-25 14:25:14 -0500472 configuration's :term:`MACHINE_FEATURES`, effectively disabling RTC
Andrew Geisslerc9f78652020-09-18 14:11:35 -0500473 support for that particular machine.