The PICL tree is the repository of all the nodes and properties created by the plug-in modules to represent the platform configuration. Every node in the PICL tree is an instance of a well-defined PICL class. The name of the base PICL class is picl, which defines a basic set of properties that all nodes in the tree must possess. Two of those properties are name and _class, where name contains the name of the node, and the _class contains the PICL class name of the node. Certain nodes in the PICL tree have well-known names. For example, the name of the root node of the PICL tree is / and the name of the root node of the sub-tree containing platform device nodes is platform.

The PICL plug-in modules are shared objects that publish platform-specific data in the PICL tree. They are located in well-known directories so that the daemon can locate and load them.

Plug-in modules are located in one of the following plug-in directories depending on the plaform-specific nature of the data that they collect and publish:

/usr/platform/'uname -i'/lib/picl/plugins /usr/platform/'uname -m'/lib/picl/plugins

A plug-in module can specify its dependency on another plug-in module using the -l or -R linker option. The plug-ins are loaded by the daemon using dlopen(3DL) according to the specified dependencies. Each plug-in module must define a .init section, which is executed when the plug-in module is loaded, to register themselves with the daemon. See picld_plugin_register(3PICLTREE) for additional information on plug-in registration.

The plug-in modules use the libpicltree(3PICLTREE) interface to publish nodes and properties in the PICL tree so that clients can access them.

When the PICL daemon invokes the initialization routine of the plug-in module, the plug-in collects the platform information and creates nodes and/or properties to represent the configuration in the PICL tree. A plug-in can create additional threads to monitor the platform configuration and update the PICL tree with any changes. This enables a PICL plug-in to operate as a daemon within the PICL framework.

An environmental monitor is an example of a plug-in module that uses a thread to monitor the temperatures and fan speeds of the platform, then publishes the environmental information in the PICL tree so clients can access them.

Clients use the libpicl(3PICL) interface to send requests to picld for accessing the PICL tree.