Systems Programming Welcome all! Visiting Card . . . some more ...

Welcome all!
Systems Programming
00. Introduction
Alexander Holupirek
Database and Information Systems Group
Department of Computer & Information Science
University of Konstanz
Summer Term 2008
c○ 1995 United Feature Syndicate, Inc. (NYC), scottadams@aol.com
Visiting Card
. . . some more details
Alexander Holupirek
alexander.holupirek@uni-konstanz.de
http://www.inf.uni-konstanz.de/~holupire
¨ 88 4440 E 217
◮ E-mail is the best way to reach me.
◮ You are welcome in my office whenever you have a question
(no need to make to make an appointment first).
Database and Information Systems Group (DBIS)
Wissenschaftlicher Angestellter (since 08/2006)
Prof. Marc H. Scholl
http://www.inf.uni-konstanz.de/dbis
Studies: Bachelor & Master IE
Private: married, 3 kids

Your Tutors
Organizational Matters
Jochen Oekonomopulos
jochen.oekonomopulos@uni-konstanz.de
Enrolled in master studies Information Engineering
Thomas Zink
thomas.zink@uni-konstanz.de
Enrolled in master studies Information Engineering
Website for this course
◮ Please check this site regulary for latest information.
http://www.inf.uni-konstanz.de/dbis/teaching/ss08/sys/
Schedule (OK for everybody?)
◮ Monday, 18:00-19:30, Room C 252
◮ Tuesday, 18:00-19:30, Room D 247/Computer Pool
How you will benefit most from this course
How you will benefit most from this course (cont.)
Assignments & Tutorials
◮ Work on the weekly assignments (pass > 80%).
◮ Hand them in on time.
◮ Jochen and Thomas will revise them.
◮ Attend the tutorials and discussion of solutions.
◮ Tuesday, 18:00-19:30, Room D 247/Computer Pool
Lecture Material
◮ Use the material provided on the course website to prepare for
the lectures.
◮ Don’t hesitate to ask questions.
◮ Let me know if I can improve the lecture material and/or its
presentation

How you will benefit most from this course (cont.)
How you will benefit most from this course (cont.)
Account & Mailinglist
◮ Use the “Account Tool” to register to the course
◮ You will automagically become a member on the mailinglist
sys S08@inf.uni-konstanz.de
◮ Feel free to post and discuss problems, questions, comments
on that list.
◮ Make sure to receive the e-mails 1
◮ Any information about changes etc. will be posted there.
Examination and Credits
◮ Pass the examination at the end of the semester
◮ Examination date: July, 15th (pending)
◮ 6 ECTS, Angewandte Informatik
Have fun!
1 These are sent to @inf.uni-konstanz.de
Literature
Literature
The IEEE and The Open Group.
Single UNIX Specification, Version 3, 2004 Edition.
http://www.unix.org/single unix specification/
Brian W. Kernighan, Dennis M. Ritchie.
The C Programming Language.
ISBN 0-13-110370-9, 1988, 41th Printing.
Prentice Hall Software Series
W. Richard Stevens, Stephen A. Rago.
Advanced Programming in the UNIX R○ Environment.
ISBN 978-0201433074
Addison-Wesley Professional; 2nd edition (June 27, 2005)

What is this course about?
The UNIX System Interface
Systems Programming
◮ With systems we mean operating systems
◮ With programming we mean using the interface an operating
system (OS) provides
◮ With OS we mean UNIX-like OSs
Operating System
◮ Layer of software on top of bare hardware
◮ Shields programmers from the complexity of the hardware
◮ Presents an interface (of a virtual machine) that is easier to
understand and program
The UNIX operating system provides its services through a set of
system calls, which are in effect functions within the operating
system that may be called by user programs.
◮ Syscalls determine a direct interface to the kernel
◮ Employed for maximum efficiency
◮ Access some facility that is not the libraries
◮ The service calls available in the interface vary from OS to
OS, however the underlying concepts tend to be similar
◮ ANSI C library is (in many cases) modeled on UNIX facilities
Standardization of the UNIX System Interface
During the 1980s the proliferation of UNIX versions and differences
between them led many large users (such as the U.S. government)
to call for standardization.
◮ Among others ANSI 2 C and the IEEE 3 POSIX emerged
◮ POSIX stands for Portable Operating System Interface
◮ POSIX refers to a family of related standards 4
◮ POSIX originally used as synonym for IEEE Std 1003.1-1988
◮ POSIX.1 emerged as a preferred term
◮ The latest version of POSIX.1 was published on April 30th 04
◮ It is called IEEE Std 1003.1, 2004 Edition (POSIX.1)
Systems Programming with POSIX.1
application using the API
POSIX.1 system call interface
OS as “Black Box”
Figure: POSIX.1 as interface to UNIX OSs
2 American National Standards Institute
3 Institute of Electrical and Electronics Engineers
4 IEEE Std 1003.n (where n is a number) and the parts of ISO/IEC 9945

Systems vs. Kernel Programming
.
◮ Black Box Modell is suitable for systems programming
◮ Knowledge about the system’s internals, however, is beneficial
to use the system properly and to not work against it
◮ Providing the system services is (mostly) kernel programming
The joint standard
The latest version POSIX.1 has been jointly developed by the IEEE
and The Open Group 5 . As such it is both an IEEE and an Open
Group Technical Standard:
application using the API
POSIX.1 system call interface
application using the API
POSIX.1 system call interface
◮ IEEE Std 1003.1, 2004 Edition
◮ The Open Group Technical Standard Base Specifications, Issue 6
◮ It is also an international standard ISO/IEC 9945:2003
OS as “Black Box”
OS kernel
Figure: Black vs. White Box View of a UNIX System
5 http://www.opengroup.org/overview/members/membership list.htm
The Single UNIX Specification, Version 3
The Single UNIX Specification (SUSv3)
The standard is published free of charge on the web 6 as
The Single UNIX Specification, Version 3, 2004 Edition
Conceptually, this standard describes a set of
fundamental services needed for the efficient construction
of application programs. Access to these services has
been provided by defining an interface, using the C
programming language, a command interpreter, and
common utility programs that establish standard
semantics and syntax.
[IEEE/The Open Group, 2004, Preface]
The document is broken into four parts:
◮ Part 1: Base Definitions (XBD)
◮ Part 2: System Interfaces (XSH)
◮ Part 3: Shell and Utilities (XCU)
◮ Part 4: Rationale
The System Interfaces volume (XSH) 7 describes a set of system
interfaces offered to application programs by systems conformant
to this part of the Single UNIX Specification. Readers are expected
to be experienced C language programmers.
http://www.opengroup.org/onlinepubs/009695399/functions/contents.html
6 http://www.unix.org/single unix specification/
7 http://www.unix.org/version3/xsh contents.html

Part 2: System Interfaces Volume (XSH)
UNIX Architecture
applications
Because POSIX.1 specifies an interface and not an implementation,
no distinction is made between system calls and library functions.
Example
System Interface Table. Lists 1123 interfaces.
http://www.opengroup.org/onlinepubs/009695399/functions/atoi.html
http://www.opengroup.org/onlinepubs/009695399/functions/read.html
shell
system calls
kernel
library routines
System Calls - Section 2
System Calls - Section 2
The system call interface has traditionally been documented in
Section 2 of the UNIX Programmer’s Manual.
1 General commands (tools and utilities).
2 System calls and error numbers.
3 Libraries.
3p perl(1) programmer’s reference guide.
4 Device drivers.
5 File formats.
6 Games.
7 Miscellaneous.
8 System maintenance and operation commands.
9 Kernel internals.
X11 An alias for X11R6.
X11R6 X Window System.
local Pages located in /usr/local.
man(1) on OpenBSD
The system call interface has traditionally been documented in
Section 2 of the UNIX Programmer’s Manual.
0 Header files (usually found in /usr/include)
1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and
conventions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]
man(1) on Linux

System Call Definition & C library functions
Library Calls - Section 3
◮ Definition of the system call interface is in the C language 8
◮ A standard technique on UNIX systems is for each system call
to have a function of the same name in the Standard C Library
◮ Those functions invoke the apt kernel service, using whatever
technique is required on the system
◮ The function may put one or more of the C arguments into
general registers and then execute some machine instruction
that generates a software interrupt in the kernel
◮ We can consider the system calls as being C functions
◮ Section 3 of the UNIX Programmer’s Manual defines the
general purpose functions available to the programmers
◮ These functions are not entry points into the kernel
◮ May use kernel’s system calls, however
◮ printf(3) may invoke write(2) to perform output
◮ atoi(3) (convert ASCII string to integer) no OS at all
◮ Implementor’s view (kernel programming): Distinction
between system call vs. library function is fundamental
◮ User’s perspective (systems programming): Not as critical,
both exist to provide services for application programs, but . . .
8 Regardless of the actual implementation technique used to invoke a call
System Calls vs. Library Calls
Essentials
Example to illustrate the difference: current time and date
◮ Some OS have syscalls to return the time and another to
return the date. Special handling (switch to or from daylight
saving) is handled by the kernel or requires human intervention
◮ UNIX provides one syscall (gettimeofday(2)) that returns
the number of seconds since the Epoch 9
◮ Any interpretation (local time zone, converting to
human-readable time) is left to the user process
◮ Syscalls usually provide a minimal interface while library
functions often provide more elaborate functionality
◮ Good knowledge of C
◮ Knowledge about the services an OS provides
◮ system calls
◮ C libraries
◮ Some knowledge about kernel’s internas
◮ Some knowledge about operating system concepts
◮ Some knowledge about the underlying hardware
9 midnight, January 1, 1970, Coordinated Universal Time