Kernel Development Learning Pipeline

Syscall Basics

C system programing interactive demo

1. the most basic C program possible: main(){}

2. hello world

3. What is a system call?

   • Synchronously ask Linux to do something for you as a user program

   • Student examples: open, read, write, close

   • Use these with file descriptors to do file I/O without FILE *

   • Use man 2 xxx to learn about system call xxx

4. Working with processes

   • execve: transform one process into another

   • fork: split one process in two

   • wait: wait for a child process

Continue Syscall Demo

• Charlie demonstrated several system calls needed to complete P0, with a focus on dealing with file descriptors

• Take note that the struct stat for a file contains a mode field that specifies file permissions

• Use the dup(2) family to create unnamed pipes on your system

• When working with C strings in the kernel, we recommend passing around a pointer and a length pair rather than relying on null-termination

  • Once must take extra precaution to avoid buffer overflows in the kernel

  • While in userspace a buffer overflow is harmful, in the kernel it can be catastrophic to a system, and in a production environment, devastating to an organization

  • We will spend more time discussing security concerns later on

• Note that file descriptors are integers that index into a table of file descriptions.

• dup(2) uses the file descriptor table to connect two file descriptors to each other.

• While dup() takes an fd to duplicate, dup2() takes a second existing fd to overwrite as the other end of the pipe.