Cross Package Injector

controllers/pkg/reconcilers/cross-pkg-injector/README.md

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+# Cross Package Injector
+
+The cross package injector is a specializer that finds resources in other
+package revisions, and copies them into the subject package revision. For
+example, in the case of free5gc, the SMF needs to know and be configured with
+information from every deployed UPF. This specializer handles that case.
+
+A package wishing to recieve configuration inputs from other packages creates a
+sentinel resource with apiVersion `config.nephio.org/v1alpha1` and Kind
+`CrossPackageRequest`.
+
+```go
+type CrossPackageRequestSpec struct {
+        PackageSelector PackageSelector `json:"packageSelector"`
+        ResourceSelector ResourceSelector `json:"resourceSelector"`
+}
+
+type PackageSelector struct {
+        metav1.LabelSelector
+
+        Name *string `json:"name,omitempty"`
+}
+
+type ResourceSelector struct {
+        metav1.LabelSelector
+
+        Name *string `json:"name,omitempty"`
+        Namespace *string `json:"namespace,omitempty"`
+}
+```
+
+First, the controller will look for any PackageRevisions matching the
+PackageSelector. Note that the only the namespace matching that of the subject
+PackageRevision will be searched.
+
+Next, within each selected package, the PackageRevisionResources will be
+searched for any resources matching the ResourceSelector. These resources will
+all be injected into the subject package, and annotated to indicate that they
+were injected by this specializer. Each time this specializer reconciles, it
+will ensure that injected resources are added, removed, or updated according to
+changes in the selector matches.
+
+A package condition will be created for each injected resource. The package
+condition will not be set to True until the source package passes all of its
+readiness gates.
+
+Questions:
+ - Does the readiness check make sense? Other criteria?
+ - Should we match Draft revisions on selection, or only Published revisions? I
+   am thinking Draft, and if a new Draft pops up, we update our Draft
+   accordingly.
+ - Do we need to rename the injected resources? I am guessing we do. Should we
+   use a calculated, fixed name based on the CrossPackageRequest name, or should
+   we allow a CEL expression for the name?
+
+## PackageVariant Support
+If the subject package revision was created by a PackageVariant, this
+specializer will wait until the PackageVariant is Ready before performing any
+mutations.