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tirdwr is a STREAMS module that provides an alternate interface to a transport provider which supports the Transport Interface ("TI") functions
of the Network Services library (see Section 3N). This alternate interface allows a user to communicate with the transport protocol provider using the read(2) and write(2) system calls. The putmsg(2) and getmsg(2) system calls may also be used. However, putmsg
and getmsg can only transfer data messages between user and stream; control portions are disallowed.
The tirdwr module must only be pushed (see I_PUSH in streamio(7I)) onto a stream terminated by a transport protocol provider which supports the TI. After the tirdwr module has been
pushed onto a stream, none of the TI functions can be used. Subsequent calls to TI functions cause an error on the stream. Once the error is detected, subsequent system
calls on the stream return an error with errno set to EPROTO.
The following are the actions taken by the tirdwr module when pushed on the stream, popped (see I_POP in streamio(7I)) off the stream, or when data passes through it.
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push
- When the module is pushed onto a stream, it checks any existing data destined for the user
to ensure that only regular data messages are present. It ignores any messages on the stream that relate to process management, such as messages that generate signals to the user processes associated with
the stream. If any other messages are present, the I_PUSH will return an error with errno set to EPROTO.
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write
- The module takes the following actions on data that originated from a write system call:
- All messages with the exception of messages that contain control portions (see the putmsg and getmsg system calls) are transparently passed onto the
module's downstream neighbor.
- Any zero length data messages are freed by the module and they will not be passed onto the module's downstream neighbor.
- Any messages with control portions generate an error, and any further system calls associated with the stream fails with errno set to EPROTO.
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read
- The module takes the following actions on data that originated from the transport protocol provider.
All messages with the exception of those that contain control portions (see the putmsg and getmsg system calls) are transparently passed onto the module's upstream
neighbor. The action taken on messages with control portions will be as follows:
- Any data messages with control portions have the control portions removed from the message before to passing the message on to the upstream neighbor.
- Messages that represent an orderly release indication from the transport provider generate a zero length data message, indicating the end of file, which will be sent to the reader
of the stream. The orderly release message itself is freed by the module.
- Messages that represent an abortive disconnect indication from the transport provider cause all further write and putmsg system calls to
fail with errno set to ENXIO. All further read and getmsg system calls return zero length data (indicating
end of file) once all previous data has been read.
- With the exception of the above rules, all other messages with control portions generate an error and all further system calls associated with the stream will fail with errno set to EPROTO.
Any zero length data messages are freed by the module and they are not passed onto the module's upstream neighbor.
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pop
- When the module is popped off the stream or the stream is closed, the module takes the following action:
- If an orderly release indication has been previously received, then an orderly release request will be sent to the remote side of the transport connection.
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