Explaining Stream Head on I/O Multiplexors

Posted on 2000-05-02
Last Modified: 2010-04-21
i'm an software engineer at NEC right now I'm studying System V network programming..but i'm currently having a problem on the I/O multiplexors..especially on the stream head can anyone give me a brief description, example and explainatio about the concept of stream head?
Question by:misguided
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Accepted Solution

dgrimes earned 200 total points
ID: 2788638
This is from the SCO OpenServer Performance Guide:

The STREAMS I/O system was designed to provide a simultaneous two-way (full duplex) connection between a process running in user space and a device driver (or pseudo-device driver) linked into the kernel. The topmost level within the kernel with which the user process communicates is known as the stream head.

Using STREAMS has the advantage that it allows the processing of I/O between an application and a device driver to be divided into a number of functionally distinct layers such as those required by network architectures that implement TCP/IP or the Open Systems Interconnection (OSI) 7-layer model.

The Streams I/O mechanism is based on the flow of messages from the stream head to a device driver, and in the oposite direction, from the device driver to the stream head. Messages that are passed away from the stream head toward the driver are seaid to be traveling downstream; messages going in the opposite direction are traveling upstream. Between the stream head and the driver, there may be a number of stream modules which process messages in addition to passing them to the next module.


There is quite a bit more but this is the brief description of the STREAMS I/O system. Hope it helps.


Author Comment

ID: 2791951
    mmmmm...i think i got it..well is just one way of communicating with devices using drivers....i got that from a book..well i guess the only way for me to understand it better is to make one right??..thanx anyway..

Expert Comment

ID: 2792586
If you wanted more information all you had to do was ask! I would have been more than happy to give all that I have. I thought you wanted a brief description. Also, if an answer given is not what you wanted then you should reject it or request clarification.

Most of the information I have and most of I have learned came for one book or another at one time or another.

If you want, I will have the points posted back to you and you can repost the question. I have no problem with doing this.

Let me know


Author Comment

ID: 2796071
no it's alright..:) i appreciate it..really..that answer was good.btw could i email you??:) maybe exchange of ideas? thanx..

Expert Comment

ID: 2796241
Sure ... my email is BTW, I do have some diagrams in this book and quite a bit more description on streams. But ... SCO has a pretty good documentation set that has all of this and more. It's at and just follow the links. There is a pretty good walk through of the logic complete with flowcharts.


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