Wed May 31 06:14:53 BST 2006

Why get Involved in POSIX?

One of the key factors leading to success for Linux and the UNIX system
has been the adoption of popular, open, standards such as the X Window
System, TCP/IP and the POSIX standards. Today we see a rapid evolution
of IT systems and applications brought about by the adoption of the
Internet, and the changes that that has brought to the way we work.
But are the standards evolving fast enough to keep pace with the changes?
This article gives a high level look at the current POSIX standardization
activity, how it works and how you can contribute to helping it keep pace.

What is POSIX?  POSIX is a registered trademark of the IEEE, and an
acronym for "Portable Operating System Interfaces".  The name POSIX was
suggested by Richard Stallman in 1986.  The most well known POSIX standard
is IEEE Std 1003.1 (or ISO Standard 9945, which is the same document))
known for short as "POSIX.1". It specifies application programming
interfaces (APIs) at the source level, and is about source code
portability. Its neither a code implementation nor an operating system,
but a standard definition of a programming interface that those systems
supporting the specification guarantee to provide to the application
programmer. Both Operating System Vendors (OSVs) and Independent Software
Vendors (ISVs) have implemented software that conforms to this standard.

The major sections of POSIX.1 are definitions, utilities (such as awk,
grep, ps, vi, etc.), headers (such as unistd.h, sys/select.h and other
C headers), threads, networking, real-time, internationalization, maths
functions etc.  In total the standard describes over 1350 interfaces .

If POSIX.1 is mentioned as a requirement for your software project then
that this does not really tell you much. POSIX.1 is large (3600 pages) and
no project needs everything (even OSVs rarely implement every optional
interface). The POSIX.1 standard itself is structured into modules
known as option groups. A minimal set of interfaces and functionality
is required for all POSIX systems. The majority of all functionality is
optional.  For a good description of options and their status in Linux
and glibc see http://people.redhat.com/~drepper/posix-option-groups.html

There are several common misconceptions about POSIX.  Originally starting
development in the mid 1980's, one common misconception is that it has
not changed for some time; it is outdated and irrelevant. The latest
version of the POSIX.1 standard was produced in 2001 and updated in 2004,
and is known as IEEE Std 1003.1, 2004 Edition.  Work is now underway to
revise the standard to produce a new revision in 2008.  While the new
versions of the standard are in general upwardly compatible with the
original, there are many hundreds of interfaces that have been added
since then. Your participation is needed to help keep it up to date and to
keep pace with the developments in the industry.

Another common misconception is that you need to be
an IEEE member to participate.  The latest edition was
developed by the Austin Group, an open working group found at
http://www.opengroup.org/austin/. Participation is free and open
to all interested parties (you just need to join the mailing list).
Decisions are made by concensus; sometimes concensus is easily reached,
and sometimes only after heated discussion!  The more people involved
in such discussions, the more likely that when concensus is reached,
it is the right decision that is made. That's why your participation
and involvement is so important. Readers should note however that the
mailing lists are not a technical support forum.  All the major UNIX
players and open source distributions are represented on the Austin Group.

Today the approach to the POSIX standard development is one of "write
once, adopt everywhere", with a single open technical working group and
the resulting documents being adopted by IEEE as the POSIX standard,
adopted by The Open Group as the Base Specifications of the Single UNIX
Specification and by the International Standards Organization as an
international standard (which in turn means that it may be a national
standard in your country; for example, the British Standards Institute
has adopted ISO 9945 as a BS).

So does this mean that the POSIX.1 standard is complete and perfect?  No,
like any large product it has bugs, and there is an ongoing bug reporting
and fixing process to refine the document as implementation experience
grows. Whilst the standard cannot change overnight there is a mechanism
both to make regular technical corrections and also to collect items for
future directions. To report a bug or suggest a change please use the
defect report form at http://www.opengroup.org/austin/defectform.html .

Is POSIX still relevant? Yes: standard interfaces mean easier porting of
applications. The POSIX interfaces are widely implemented and referenced
in other standardization efforts, including the Single UNIX Specification
and the Linux Standard Base.

Why should you get involved? By feeding back issues with the standard
based on implementation experience the standard can be improved and
extended with new functionality, which in turn can "raise the bar of
commonality" among systems.  There is often much more to be gained
by having key functionality share a common interface and/or behave in
exactly the same way, than for it to be different.

More information on POSIX.1 and the Austin Group, including
how to join and participate is available from its web site at
http://www.opengroup.org/austin/.

The html version of the standard is freely available from The Open Group's
Single UNIX Specification web site at http://www.unix.org/version3/


Andrew Josey, Austin Group Chair