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HP-UX 11i Version 3: February 2007

Technical documentation

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tirdwr — STREAMS module for reads and writes by Transport Interface users


The tirdwr module is a STREAMS module that provides a transport user supporting the Transport Interface (TI) with an alternate interface to a transport protocol provider supporting TI. This alternate interface allows the transport user to communicate with the transport protocol provider using the read() and write() functions. It can also continue to use the putmsg() and getmsg() functions, but these functions will only transfer data messages between the user process and device stream. getpmsg() and putpmsg() should not be used with tirdwr.

The user places the tirdwr module on a device stream by calling the STREAMS I_PUSH ioctl() function. tirdwr is an alternative interface to timod(7). If timod has been pushed onto the stream, the user should use the I_POP ioctl to remove the timod module from the stream before pushing tirdwr. The tirdwr module should only be pushed onto streams which are terminated by transport providers which conform to the Transport Interface. Once the module has been pushed on the device stream the user cannot make further calls to TI functions. If the user attempts to do this, an error occurs on the stream. After the error is detected, subsequent calls fail with errno set to [EPROTO]. The user removes the tirdwr module from a device stream by calling the STREAMS I_POP ioctl() function.

Module Behavior When Pushed and Popped

When the tirdwr module is pushed on a device stream, it checks any existing messages that are destined for the user to determine their message type. If existing messages are regular data messages, it forwards the messages to the user. It ignores any messages related to process management, such as messages that generate signals to the user. If any other messages are present, it returns an error to the user request with errno set to [EPROTO].

When the tirdwr module is popped from a device stream, it checks whether an orderly release indication has been previously received from the transport protocol provider. If an orderly release indication was received, it sends an orderly release request to the remote side of the transport connection. The tirdwr module also acts this way when the device stream is closed.

Module Behavior for Reads and Writes

When the tirdwr module receives messages from the transport protocol provider that do not contain a control part (see the putmsg(2) and getmsg(2) reference pages), it transparently passes the messages to its upstream neighbor. The exception is for zero-length data messages, where the module frees the message and does not pass them to its upstream neighbor.

When the module receives messages from the transport protocol provider that contain a control part, it takes one of the following actions:

  • For data messages with a control part, it removes this part, then passes the message to its upstream neighbor.

  • For messages that represent expedited data, it generates an error. Further system calls will fail with errno set to [EPROTO].

  • For messages that represent an orderly release indication from the transport protocol provider, it generates a zero-length data message, indicating the End-of-File (EOF), and sends this message upstream to the reading process. The original message containing the orderly release indication is freed.

  • For messages that represent an abortive disconnect indication from the transport protocol provider, it causes all further write() and putmsg() calls to fail with errno set to [ENXIO]. Subsequent read() and getmsg() calls will return zero-length data messages indicating the End-of-File (EOF), once all previous data has been read.

  • For all other messages, it generates an error, and further calls will fail with errno set to [EPROTO].

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