Creating IPC channels

Overview: creating IPC channels

There are two methods for creating IPC channels: static and dynamic.

Static creation of IPC channels is simpler to implement because you can use the init description for this purpose.

Dynamic creation of IPC channels lets you change the topology of interaction between processes on the fly. This is necessary if it is unknown which specific server contains the endpoint required by the client. For example, you may not know which specific drive you will need to write data to.

Statically creating an IPC channel

The static method has the following distinguishing characteristics:

• The client and server are in the stopped state when the IPC channel is created.
• Creation of this channel is initiated by the parent process that starts the client and server (this is normally Einit).
• The created IPC channel cannot be deleted.
• To get the IPC handle and endpoint ID (riid) after the IPC channel is created, the client and server must use the endpoint locator interface (coresrv/sl/sl_api.h).

Dynamically creating an IPC channel

The dynamic method has the following distinguishing characteristics:

• The client and server are already running at the time of creating the IPC channel.
• Creation of the channel is initiated jointly by the client and server.
• The created IPC channel can be deleted.
• The client and server get the IPC handle and endpoint ID (riid) immediately after the IPC channel is successfully created.

Creating IPC channels using init.yaml

This section contains init descriptions that demonstrate the specific features of creating IPC channels. Examples of defining properties and arguments of processes via init descriptions are examined in a separate article.

The file containing an init description is usually named init.yaml, but it can have any name.

Connecting and starting a client process and server process

In the next example, two processes will be started: one process of the Client class and one process of the Server class. The names of the processes are not specified, so they will match the names of their respective process classes. The names of the executable files are not specified either, so they will also match the names of their respective classes. The processes will be connected by an IPC channel named server_connection.

init.yaml

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Dynamically created IPC channels

A dynamically created IPC channel uses the following functions:

• Name Server interface
• Connection Manager interface

An IPC channel is dynamically created according to the following scenario:

1. The following processes are started: client, server, and name server.
2. The server connects to the name server by using the NsCreate() call and publishes the server name, interface name, and endpoint name by using the NsPublishService() call.
3. The client uses the NsCreate() call to connect to the name server and then uses the NsEnumServices() call to search for the server name and endpoint name based on the interface name.
4. The client uses the KnCmConnect() call to request access to the endpoint and passes the found server name and endpoint name as arguments.
5. The server calls the KnCmListen() function to check for requests to access the endpoint.
6. The server accepts the client request to access the endpoint by using the KnCmAccept() call and passes the client name and endpoint name received from the KnCmListen() call as arguments.

The server can use the NsUnPublishService() call to unpublish endpoints that were previously published on the name server.

The server can use the KnCmDrop() call to reject requests to access endpoints.