Configuration options live in a hierarchy of packages and components. By default a given option's position in the hierarchy is a simple consequence of its position within the CDL scripts. Packages are generally placed at the top-level of the configuration. Any components or options that are defined at the same level as the cdl_package command in a package's top-level CDL script are placed immediately below that package in the hierarchy. Any options or components that are defined in the body of a cdl_package or cdl_component command, or that are read in as a result of processing a component's script property, will be placed immediately below that package or component in the hierarchy.
In some circumstances it is useful to specify an alternative position
in the hierarchy for a given option. For example it is often
convenient to re-parent device driver packages below
CYGPKG_IO in the configuration hierarchy, thus
reducing the number of packages at the top level of the hierarchy and
making navigation easier. The parent property can be used to achieve
this.
The parent property takes a single argument, which should be the name of a package or component. The body of a cdl_option or other CDL entity can contain at most one parent property.
Although the parent property affects an option's position in the overall hierarchy and hence whether or not that option is active, a re-parented option still belongs to the package that defines it. By default any #define's will be exported to that package's configuration header file. Any compile properties can only reference source files present in that package, and it is not directly possible to cause some file in another package to be built by re-parenting.
As a special case, if an empty string is specified for the parent then the option is placed at the top of the hierarchy, ahead of any packages which are not explicitly re-parented in this way. This facility is useful for configuration options such as global preferences and default compiler flags.
Tip: If an option is re-parented somewhere below another package and that other package is not actually loaded, the option is an orphan and its active/inactive state is undefined. In such cases it is a good idea for the owning package to require the presence of the other one. Unfortunately this technique does not work if a package as a whole is reparented below another one that has not been loaded: the package is orphaned so it may be automatically inactive, and hence any requires properties would have no effect.