|
The primary task of the put() routine is to coordinate the passing of messages from one queue to the next in a stream. The put() routine is called by the
preceding stream component (stream module, driver, or stream head). put() routines are designated ``write'' or ``read'' depending on the direction of message flow.
With few exceptions, a streams module or driver must have a put() routine. One exception is the read side of a driver, which does not need a put() routine because
there is no component downstream to call it. The put() routine is always called before the component's corresponding srv(9E) (service) routine, and so put() should be used for the immediate processing of messages.
A put() routine must do at least one of the following when it receives a message:
- pass the message to the next component on the stream by calling the putnext(9F) function;
- process the message, if immediate processing is required (for example, to handle high priority messages); or
- enqueue the message (with the putq(9F)
function) for deferred processing by the service srv(9E) routine.
Typically, a put() routine will switch on message type, which is contained in the db_type member of the datab structure pointed to by mp. The action taken by the put() routine depends on the message type. For example, a put() routine might process high priority messages, enqueue normal
messages, and handle an unrecognized M_IOCTL message by changing its type to M_IOCNAK (negative acknowledgement) and
sending it back to the stream head using the qreply(9F) function.
The putq(9F) function can be used as a module's put() routine when no special processing is required and all messages are to be enqueued for the srv(9E) routine.
|
