Intro

• xv6 is a small (~6000 loc) OS from MIT built as a teaching tool for OSes.
• there are two implementations, the risc-v one will be used, but there is an x86-64 one.
• QEMU is used for emulating the OS, since you probably don’t want to run it on real hardware (a buggy OS could fry hardware)

The Codebase

• ~6000 loc of C, 300 lines of assembly.
• Processes run in their own virtual address spaces using page tables
• pipes are supported
• multitasking with time slicing

System Calls

• only 21 implemented, compared to hundreds
• fork, wait, exit, pipe, open/close/read/write, kill, exec, link, unlink
• Used to implement userspace, like cat, echo, grep, kill, ln, ls, mkdir, rm, wc

Limitations

• No user authentication
• No network support
• No virtual memory paging
• Only two device drivers
• limited userspace + system calls