Using system calls – and when not to use them
System calls are an exciting topic in any conversation about Unix and Linux. They are one of the lowest parts when it comes to system programming in Linux. If we were to look at this from a top-down approach, the shell and the binaries we run would be at the top. Just below that, we have the standard C library functions, such as printf(), fgets(), putc(), and so on. Below them, at the lowest levels, we have the system calls, such as creat(), write(), and so on:
Figure 3.1 – High-level functions and low-level functions
When I talk about system calls here in this book, I mean system calls as C functions provided by the kernel, not the actual system call table. The system call functions we use here reside in user space, but the functions themselves execute in kernel space.
Many of the standard C library functions, such as putc(), use one or more system call functions behind the curtains. The putc...
