Feature Backfilling
- 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 DISTRO_FEATURES
- and MACHINE_FEATURES.
+ Sometimes it is necessary to add a new feature option to the
+ MACHINE_FEATURES
+ or DISTRO_FEATURES
+ lists and have it affect all configurations.
+ For example, suppose new functionality is developed and it must be enabled
+ by default for all configurations.
- 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
- DISTRO_FEATURES_BACKFILL
- within meta/conf/bitbake.conf.
- This means that "pulseaudio"
- is automatically added to DISTRO_FEATURES without the distro
- configuration needing to be updated to do so itself.
- Those who do not want PulseAudio support can add "pulseaudio" to
- DISTRO_FEATURES_BACKFILL_CONSIDERED
- in their distro .conf file and this will disable adding "pulseaudio" to
- DISTRO_FEATURES.
-
+ Sometimes it is also necessary to disable (remove) a feature
+ option, which has been previously enabled by default, from the machine or distro lists.
+ For example, perhaps a mandatory distro feature becomes optional.
+ How can you remove the feature option from the
+ DISTRO_FEATURES list
+ without disturbing all the existing configurations that still
+ might need the feature?
+ Feature backfilling allows you "backfill" the feature into all the
+ configurations and then lets you selectively prevent the feature from
+ being added to MACHINE_FEATURES and
+ DISTRO_FEATURES lists.
+
- 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
- MACHINE_FEATURES_BACKFILL
- within meta/conf/bitbake.conf.
- This means that "rtc"
- is automatically added to MACHINE_FEATURES without the
- machine configuration needing to be updated to do so itself.
- For machines that not need RTC support can add "rtc" to
- MACHINE_FEATURES_BACKFILL_CONSIDERED
- in their machine .conf file and this will disable adding "rtc" to
- MACHINE_FEATURES.
+ 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.
+ However, you might need to disable the feature for your
+ distro.
+ You can disable the feature without affecting
+ other existing distro configurations that need PulseAudio support
+ by doing the following:
+
+ Add "pulseaudio" to
+ DISTRO_FEATURES_BACKFILL
+ within your meta/conf/bitbake.conf file.
+ Adding the feature option causes the build process
+ to automatically add "pulseaudio" to
+ DISTRO_FEATURES without the need to
+ update any distro configurations.
+ This step by itself enables the feature
+ for all distros and consequently ensures that existing
+ configurations that still need the feature are
+ undisturbed.
+ Add "pulseaudio" to
+ DISTRO_FEATURES_BACKFILL_CONSIDERED
+ in your distro's .conf file.
+ Adding the feature option to this variable when it also
+ exists in the DISTRO_FEATURES_BACKFILL
+ variable prevents the build system from adding the feature option to
+ 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.
+ However, your target device does not have this capability.
+ You can disable RTC support for your device without
+ affecting other machines where RTC support should remain enabled
+ by doing the following:
+
+ Add "rtc" to MACHINE_FEATURES_BACKFILL
+ within your meta/conf/bitbake.conf.
+ Adding the feature option causes the build process
+ to automatically add "rtc" to
+ MACHINE_FEATURES without the need to
+ update any machine configurations.
+ This step by itself enables RTC support for all machines
+ and consequently ensures that existing configurations
+ that still need the feature are undisturbed.
+ Add "rtc" to
+ MACHINE_FEATURES_BACKFILL_CONSIDERED
+ in your machine's .conf file.
+ Adding the feature option to this variable when it also
+ exists in the MACHINE_FEATURES_BACKFILL
+ variable prevents the build system from adding the feature option to
+ MACHINE_FEATURES, effectively disabling
+ RTC support for feature that particular machine.
+
+