STREAMS

In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.

STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing terminal I/O (line discipline) and networking subsystems. In System V Release 4, the entire terminal interface was reimplemented using STREAMS^[1]. An important concept in STREAMS is the ability to push drivers — custom code modules that can modify the functionality of a network interface or other device — together to form a stack. Several of these drivers can be chained together in order.

History

STREAMS was first introduced in Eighth Edition Research Unix by Dennis Ritchie, where it was used for the terminal I/O subsystem and the TCP/IP protocol. This version fit the new functionality under the existing device I/O system calls (open, close, read, write, and ioctl),^[2] and its application was limited to terminal I/O and protocols providing pipe-like I/O semantics. It was ported to System V Release 3 by Robert Israel, Gil McGrath, Dave Olander, Her-Daw Che, and Maury Bach as part of a wider framework intended to support a variety of transport protocols, including TCP/IP, ISO Class 4 transport, SNA LU 6.2, and the AT&T NPACK protocol (used in RFS).^[3] It was first released with the Network Support Utilities (NSU) package of UNIX System V Release 3.^[4] This port added the putmsg, getmsg, and poll system calls, which are nearly equivalent to the send, recv, and select calls from Berkeley sockets. The putmsg and getmsg system calls were orignally called send and recv,^[5] but were renamed to avoid namespace conflict.^[6] In System V Release 4, STREAMS was extended and used for the terminal I/O framework and pipes, providing useful new functionality like bi-directional pipes and file descriptor passing.^[7] A port for Unicos was also produced.

Concurrent with the System V Release 3 port, AT&T developed protocol-independent STREAMS message passing guidelines for the link,^[8] network,^[9] and transport layers^[10] of the OSI model (layers 2-4). Due to the typically close implementation coupling of the network and transport protocols in a given protocol stack, and the typical practice of implementing layers 5-7 outside of the kernel, only the link^[11] and transport layer^[12] STREAMS service interfaces were later standardized by X/Open. In conjunction with the transport message passing model, the Transport Layer Interface (later adopted as the X/Open Transport Interface) was defined to provide a transport protocol-independent API for application development. Also, a library supporting the session, presentation and application layers^[13] was defined and later standardized by The Open Group.^[14]

STREAMS was required for conformance with the Single UNIX Specification versions 1 (UNIX 95) and 2 (UNIX 98), but as a result of the inability of the BSD and Linux flavors of UNIX to provide STREAMS, was marked as optional for POSIX compliance by the Austin Group in version 3 (UNIX 03).

Implementations

STREAMS has mostly been used in the System V Unix world; however, other implementations exist:

• Plan 9 originally used a multi-processor variant of Research Unix's Streams. During the transition to the third edition of Plan 9, Streams were further simplified to simple I/O queues.
• Mentat wrote an implementation of STREAMS.
  • Novell Netware utilizes Mentat's STREAMS in its TCP/IP stack.
  • This was licensed by Apple Computer the for use in Mac OS starting in version 7.5.2, as part of their Open Transport networking system.
    • In Mac OS X, the Classic environment uses the STREAMS architecture, but the native networking architecture is essentially Berkeley sockets.
• The Linux kernel does not include STREAMS functionality, the kernel developers consider it technically inadequate, and the compatibility layers in Linux for other operating systems convert STREAMS operations into sockets as early as possible ^[15].
  • LiS (Linux STREAMS) adds STEAMS functionality on Linux^[16][17]
  • OpenSS7 offers Fast STREAMS on Linux^[18].
• FreeBSD has basic support for STREAMS-related system calls, as required by SVR4 binary compatibility layer.
• The Windows NT kernel offered a full port of STREAMS as the streams.sys binary. NT DDK even had a chapter on STREAMS, going as late as NT4 though in NT4 DDK it was declared obsolete.
  • It is sometimes claimed that an early port of TCP/IP for Windows NT by Lachman Associates (?) included a full implementation of the System V.3 STREAMS model. It was really implemented based on STREAMS, and used the streams.sys binary. From NT 3.5 (? or 3.51) up, TCP/IP was remade completely, according to some sources, by adopting the one from MS LAN Manager for OS/2 1.x

Notes

References

• Goodheart, Berny; James Cox (1994). The magic garden explained: the internals of UNIX System V Release 4, an open-systems design. Australia: Prentice Hall. ISBN 0-13-098138-9. 
• Open Group (1999), "Transport Provider Interface (TPI) Specification", Open Group CAE Specification (Berkshire, UK: Open Group Publication) 
• Open Group (September 1993), "ACSE/Presentation Services API (XAP)", X/Open CAE Specification (Berkshire, UK: X/Open Company Limited) XAP (c303), ISBN 1-872630-91-X 
• Pajari, George (1992) [1991]. Writing UNIX Device Drivers (2nd Printing, 1st ed.). Reading, MA: Addison-Wesley. ISBN 0-201-52374-4. 
• Ritchie, Dennis M. (October 1984). "A Stream Input-Output System". AT&T Bell Laboratories Technical Journal 63, No. 8 Part 2 (AT&T): 1897–1910. http://cm.bell-labs.com/cm/cs/who/dmr/st.html. Retrieved 2006-05-19. 
• Stevens, W. Richard (1993). Advanced Programming in the UNIX Environment (15th Printing, 1st ed.). Reading, MA: Addison-Wesley. ISBN 0-201-56317-7. 
• Thomas, Rebecca; Lawrence R. Rogers, Jean L. Yates (1986). Advanced Programmers Guide to UNIX System V. Berkeley, CA: Osborne McGraw-Hill. ISBN 0-07-881211-9. 
• UNIX International (August 20, 1001), Data Link Provider Interface (DLPI) Specification, UNIX International Publication (Revision 2.0.0, Draft 2 ed.), Parsippany, N.J.: UNIX International Press, http://www.openss7.org/doc/dlpi.pdf, retrieved 2009-07-27 
• UNIX International (August 17, 1992), Network Provider Interface (NPI) Specification, UNIX International Publication (Revision 2.0.0, Draft 2 ed.), Parsippany, N.J.: UNIX International Press, http://www.openss7.org/doc/npi.pdf, retrieved 2009-07-27 
• UNIX International (December 10, 1992), Transport Provider Interface Specification, UNIX International Publication (Revision 1.5, Draft 2 ed.), Parsippany, N.J.: UNIX International Press, http://www.openss7.org/doc/tpi.pdf, retrieved 2009-07-27 
• UNIX International (October 25, 1990), ACSE/Presentation Library Interface (APLI) Specification, UNIX International Publication (Draft ed.), Parisppany, N.G.: UNIX International Press 
• Waite Group (1987). Mitchel Waite. ed. UNIX Papers (2nd Printing, 1st ed.). Indianapolis, IN: Howard W. Sams & Company. ISBN 0-672-22578-6. 

External links

• The original stream(4) manual from Unix 8th Edition
• The STREAMS framework in Digital UNIX — from the Digital UNIX Network Programmer's Guide
• Sun STREAMS Programming Guide