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| -rw-r--r-- | documentation/poky-ref-manual/ref-features.xml | 51 | 
1 files changed, 24 insertions, 27 deletions
diff --git a/documentation/poky-ref-manual/ref-features.xml b/documentation/poky-ref-manual/ref-features.xml index 7d98464126..063eaadc43 100644 --- a/documentation/poky-ref-manual/ref-features.xml +++ b/documentation/poky-ref-manual/ref-features.xml  | |||
| @@ -178,38 +178,35 @@ | |||
| 178 | <title>Feature Backfilling</title> | 178 | <title>Feature Backfilling</title> | 
| 179 | 179 | ||
| 180 | <para> | 180 | <para> | 
| 181 | Sometimes it is necessary to control functionality enabled by features | 181 | Sometimes it is necessary in the OpenEmbedded build system to extend | 
| 182 | that are listed with | ||
| 183 | <link linkend='var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></link> | 182 | <link linkend='var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></link> | 
| 184 | and <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>. | 183 | or <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link> | 
| 185 | For example, some functionality exists that is enabled | 184 | to control functionality that was previously enabled and not able | 
| 186 | by default for all configurations. | 185 | to be disabled. | 
| 187 | For these cases, the metadata, as shipped with the Yocto Project, ensures | 186 | For these cases, we need to add an | 
| 188 | the feature is "backfilled" into all the specific distro | 187 | additional feature item to appear in one of these variables, | 
| 189 | and machine configurations. | 188 | but we do not want to force developers who have existing values | 
| 190 | You can see how this is done by finding the | 189 | of the variables in their configuration to add the new feature | 
| 190 | in order to retain the same overall level of functionality. | ||
| 191 | Thus, the OpenEmbedded build system has a mechanism to | ||
| 192 | automatically "backfill" these added features into existing | ||
| 193 | distro or machine configurations. | ||
| 194 | You can see the list of features for which this is done by | ||
| 195 | finding the | ||
| 191 | <link linkend='var-DISTRO_FEATURES_BACKFILL'><filename>DISTRO_FEATURES_BACKFILL</filename></link> | 196 | <link linkend='var-DISTRO_FEATURES_BACKFILL'><filename>DISTRO_FEATURES_BACKFILL</filename></link> | 
| 192 | and <link linkend='var-MACHINE_FEATURES_BACKFILL'><filename>MACHINE_FEATURES_BACKFILL</filename></link> | 197 | and <link linkend='var-MACHINE_FEATURES_BACKFILL'><filename>MACHINE_FEATURES_BACKFILL</filename></link> | 
| 193 | variables in the <filename>meta/conf/bitbake.conf</filename> file. | 198 | variables in the <filename>meta/conf/bitbake.conf</filename> file. | 
| 194 | </para> | 199 | </para> | 
| 195 | 200 | ||
| 196 | <para> | 201 | <para> | 
| 197 | Because certain functionality is enabled across all configurations as | 202 | Because such features are backfilled by default into all | 
| 198 | described in the previous paragraph, it also becomes necessary | 203 | configurations as described in the previous paragraph, developers | 
| 199 | to give the developer the ability to disable (remove) a feature | 204 | who wish to disable the new features need to be able to selectively | 
| 200 | from a particular configuration. | 205 | prevent the backfilling from occurring. | 
| 201 | For example, suppose you have a machine feature that needs to be | 206 | They can do this by adding the undesired feature or features to the | 
| 202 | disabled but the metadata has backfilled it across all configurations as enabled. | 207 | <link linkend='var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></link> | 
| 203 | You need to be able to remove the feature from your configuration's | 208 | or <link linkend='var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></link> | 
| 204 | <filename>MACHINE_FEATURES</filename> | 209 | variables for distro features and machine features respectively. | 
| 205 | without disturbing existing configurations that still | ||
| 206 | might need the functionality? | ||
| 207 | </para> | ||
| 208 | |||
| 209 | <para> | ||
| 210 | Feature backfilling allows you to selectively prevent a feature from | ||
| 211 | being backfilled to <filename>MACHINE_FEATURES</filename>, | ||
| 212 | <filename>DISTRO_FEATURES</filename>, or both. | ||
| 213 | </para> | 210 | </para> | 
| 214 | 211 | ||
| 215 | <para> | 212 | <para> | 
| @@ -226,7 +223,7 @@ | |||
| 226 | You can disable the feature without affecting | 223 | You can disable the feature without affecting | 
| 227 | other existing distro configurations that need PulseAudio support | 224 | other existing distro configurations that need PulseAudio support | 
| 228 | by adding "pulseaudio" to | 225 | by adding "pulseaudio" to | 
| 229 | <link linkend='var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></link> | 226 | DISTRO_FEATURES_BACKFILL_CONSIDERED | 
| 230 | in your distro's <filename>.conf</filename> file. | 227 | in your distro's <filename>.conf</filename> file. | 
| 231 | Adding the feature to this variable when it also | 228 | Adding the feature to this variable when it also | 
| 232 | exists in the <filename>DISTRO_FEATURES_BACKFILL</filename> | 229 | exists in the <filename>DISTRO_FEATURES_BACKFILL</filename> | 
| @@ -243,7 +240,7 @@ | |||
| 243 | You can disable RTC support for your device without | 240 | You can disable RTC support for your device without | 
| 244 | affecting other machines that need RTC support | 241 | affecting other machines that need RTC support | 
| 245 | by adding the feature to your machine's | 242 | by adding the feature to your machine's | 
| 246 | <link linkend='var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></link> | 243 | MACHINE_FEATURES_BACKFILL_CONSIDERED | 
| 247 | list in the machine's <filename>.conf</filename> file. | 244 | list in the machine's <filename>.conf</filename> file. | 
| 248 | Adding the feature to this variable when it also | 245 | Adding the feature to this variable when it also | 
| 249 | exists in the <filename>MACHINE_FEATURES_BACKFILL</filename> | 246 | exists in the <filename>MACHINE_FEATURES_BACKFILL</filename> | 
