Advanced Operating Systems (CS 202) Presenter today: Khaled N. Khasawneh Instructor: Nael Abu-Ghazaleh Jan, 11, 2016

Today Introduction to xv6

v6 Sixth Edition Unix a.k.a. Version 6 Unix First public release of Unix out of Bell Labs By Ken Thompson & Dennis Ritchie, 1975 Designed for DEC PDP-11* Original source code still available: http://minnie.tuhs.org/cgi-bin/utree.pl

Why not using v6 PDP11 is not used nowadays Missing some of the key issues in modern Oses Paging Multicore Luckily ..

xv6 xv6 is an MIT reimplementation of Unix v6 Runs on x86 But we will run it on top of QEMU Smaller than v6 Preserve basic structure (Processes, files, pipes. etc.) Runs on multicores Got paging in 2011  To understand it, you’ll need to reads it’s source code It’s not that hard Textbook/commentary: xv6: a simple, Unix-like teaching operating system Online: http://pdos.csail.mit.edu/6.828/2012/xv6/book-rev7.pdf Machine emulator

Why xv6? Why study an old OS instead of Linux, Solaris, or Windows? 1: Big enough To illustrate basic OS design & implementation 2: Small enough To be (relatively) easily understandable 3: Similar enough To modern Oses Once you’ve explored xv6, you will find your way insde kernels such as Linux

XV6 Structure Monolithic kernel Provides services to running programs Processes uses system calls to access system services When a process call a system call Execution will enter the the kernel space Perform the service Return to the user space

XV6 system calls

XV6 system calls (2)