6.2. Preferences and Providers

+6.2. Preferences and Providers

+ Once all the .bb files have been + parsed, BitBake starts to build the target (core-image-sato + in the previous section's example) and looks for providers of that target. + Once a provider is selected, BitBake resolves all the dependencies for + the target. + In the case of core-image-sato, it would lead to + packagegroup-core-x11-sato, + which in turn leads to recipes like matchbox-terminal, + pcmanfm and gthumb. + These recipes in turn depend on eglibc and the toolchain. +

+ Sometimes a target might have multiple providers. + A common example is "virtual/kernel", which is provided by each kernel package. + Each machine often selects the best kernel provider by using a line similar to the + following in the machine configuration file: +

+     PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
+

+ The default PREFERRED_PROVIDER + is the provider with the same name as the target. +

+ Understanding how providers are chosen is made complicated by the fact + that multiple versions might exist. + BitBake defaults to the highest version of a provider. + Version comparisons are made using the same method as Debian. + You can use the + PREFERRED_VERSION + variable to specify a particular version (usually in the distro configuration). + You can influence the order by using the + DEFAULT_PREFERENCE + variable. + By default, files have a preference of "0". + Setting the DEFAULT_PREFERENCE to "-1" makes the + package unlikely to be used unless it is explicitly referenced. + Setting the DEFAULT_PREFERENCE to "1" makes it likely the package is used. + PREFERRED_VERSION overrides any DEFAULT_PREFERENCE setting. + DEFAULT_PREFERENCE is often used to mark newer and more experimental package + versions until they have undergone sufficient testing to be considered stable. +

+ In summary, BitBake has created a list of providers, which is prioritized, for each target. +