COMP 3000 Essay 1 2010 Question 2

Question

How do the available system calls in modern versions of the Linux Kernel (2.6.30+) compare with the system calls available in the earliest versions of UNIX? How has the system call interface been expanded, and why? Focus on major changes or extensions in functionality.

Answer

A system call is a mean by which programs in the user space can access kernel services. Systems calls vary from operating system to operating system, although the underlying concepts tends to be the same. In general, a process is not supposed to be able to access the kernel directly. It can'y access kernel memory and it can't call kernel functions. The CPU prevents this (called "protected mode"). System calls are an exception to this rule. For example, older x86 processors used an interrupt mechanism to go from user-space to kernel-space, but newer processor (PentiumII+) provided instructions that optimize this transition (using sysenter and sysexit instructions). All system calls are small programs built using the C programming language.

The Unix and Linux systems calls are roughly grouped into 6 categories: file management, device management, information maintenance, process control, communications and miscellaneous calls. The miscellaneous calls are all the ones that don’t really fit in the other categories, like system calls dealing with errors. Today, the Unix and Linux operating system contains hundreds of system calls but in general, they all came from the 35 system calls that came with one of the original UNIX OS in the early 70s. In the next paragraphs, we’re going to described the various system calls in each of the categories mentioned above, their evolution through history (major changes in functionality) and a comparison with the earliest versions of UNIX.

References

Here is the original manual --Lmundt 18:29, 7 October 2010 (UTC) http://cm.bell-labs.com/cm/cs/who/dmr/1stEdman.html

Linux Programmer's Manual, Linux man-pages project. http://www.kernel.org/doc/man-pages/