Courses/Computer Science/CPSC 457.W2013/Lecture Notes/Creation

Process Creation

In this session, we will continue our examination of how processes come to be. We will start by considering what a process is (see task_struct). We will also briefly trace our understanding of control flow involving invoking parts of the system call interface.

We will also have a multi-perspective look at the routines

• execve
• fork / clone / vfork

involved in process creation. We will glance over the source code of the kernel's routines for creating (or cloning) a process and loading an executable (i.e., ELF) image into a process address space. They lead to a chain of procedures in the OS that is a bit deeper and more complex than the system call interface might otherwise imply.

Notes

• slides from today (augmented deck from last time)
• NSERC USRA 2012 announcement
• Virtual Machines (needed for homework assignments and tutorial sessions)
  • do_fork routine: http://lxr.linux.no/#linux+v2.6.27.41/kernel/fork.c#L1314
  • copy_process routine: http://lxr.linux.no/#linux+v2.6.27.41/kernel/fork.c#L887

Last time we saw how we could talk directly to the kernel via the syscall interface

• now let's write a program using write(2)
• compare this with our assembly version
• what is this interface?
• where are the parts documented?
  • manual pages
  • show locations of syscall number definitions
• what is the actual mechanism?
  • trace the ``control flow of making a system call
  • phrack article on IDT

Today, we'll look at what a process is

• what is the purpose of an OS?
  • to support the execution of progams
  • protection
  • multiplex resources
  • what is an OS? (a kernel)
    • a kernel is just a compressed ELF
• what is a process?
  • a process is ``a program in execution
  • PCB
  • PAS
  • what parts of the syscall API can be used to create a process?
• we'll deal with an in-depth examination of the process address space later

Readings

• MOS: Section 2.1: Processes (this should be partly review of what we've talked about in class)
• MOS: Section 3.2.1: The Notion of an Address Space
• MOS: Section 3.7 (all except 3.7.2) (this should review some of what we touched on in the previous class and lay some groundwork for talking about memory management)
• MOS: Section 10.2.5 (Linux kernel structure)
• MOS: Section 10.3.1 (about processes in Linux) should reinforce some class discussion