The put(9E) and srv(9E) interfaces process messages as they pass through the queue. Messages are generally processed by type, resulting in a modified message, one or more new messages, or no message at all. The message usually continues in the same direction it was passing through the queue, but can be sent in either direction. A put(9E) procedure can place messages on its queue as they arrive, for later processing by the service procedure. For a more detailed explanation of put and service, see Chapter 8, Messages - Kernel Level.
Some kernel operations are explained here to show you how to manipulate the driver or module appropriately.