Libgtop Reference Manual: Overview

## Overview

This section should give you a short overview on how LibGTop was developed, which things needed to be considered and how it works.

### Interface Design: Things that need to be considered

At the very beginning, it was necessary to collect all the data the library part should provide and put them into some C structures. This was not that easiy as it might sound since LibGTop should be portable to any modern UNIX system with a common library part on all those systems, but the data that should be returned vary from system to system. For instance some systems support shared memory, but some others may not.

The header files where we define these C structures (which are system-independent) are shared between client and server. This way we can call the system dependent code directly where we do not need any special privileges to do so.

All of those structures contain a @code{flags} member which is interpreted as a bit mask and tells the caller of the library functions which of the fields in the returned structure are valid and which are not.

### Server Implementation: The LibGTop "server"

The LibGTop @dfn{server} is a setgid/setuid binary which contains all the system dependent code which needs special privileges. It is only build if it's required on the current system (for instance, the Linux kernel provides all the required data via its @file{/proc} filesystem so we do not need the server at all) and it only contains the @dfn{features} which need privileges.

Whenever we do not need any privileges to get all the data for some of the requested structures (here called @dfn{features}) the library calls the sysdeps code directly rather than using the server.