GOODMIA2024 / 6.S081

6.S081 Operating System Engineering Course Repo

6.S081

SP Notes

Each lab has its own branch in the repository. Labs completed so far:

Repo Branches	Lab Notes (some WIP)
🔗Lab Util
🔗Lab Syscall
🔗Lab Page tables	📒【fin】Lab Notes
🔗Lab Traps	📒【fin】Lab notes
🔗Lab Lazy page allocation	📒【fin】Lab notes
🔗Lab Cow	📒Lab notes
🔗Lab Thread	📒【fin】Lab notes
🔗Lab Lock	📒Lab notes
🔗Lab File System	📒【fin】Lab notes
🔗Lab Networking	📒【fin】Lab notes

Weekly Roadmap

Prep -> Lec video&slides -> Lab

Suggested prerequisite

in retrospect, seems that simply taking all the pre-lecture readings seriouly will do (even for os new comers)

Progress

Completed whitin 3 months (part-time).

• 【0820】init repo && materials && setup
• 【0821】reading1+lec1
• 【0824】lab util
• 【0912】prep2, lec2(slidesOnly)
• 【0915】review concepts+labUtil, lec 3 prep + live
• 【0917】lab syscall
• 【0920+】prep3, lec4+5+6, lab pgtbl
• 【0928】preps, lec 7+8, lab traps
• 【0930】preps, lec 9, lab lazy
• 【1003】prep (ch6 & code), lec 10,
• 【1005】lab cow, prep11, lec 11, lab thread
• 【1011】prep, lab lock
• 【1013】prep fs, lec 14 & lec 15
• 【~1028】prep, lec 16, lab fs
• 【1030】prep, lec 17, 18
• 【1031】lab networking, lec 19, lec 20, FIN!

W7

Prep

• chap 8
• code

lab fs:

• see notes

W6

Prep:

• chapter 6&7
• code examples

lab thread + lock:

• see notes

W5

Prep:

• chapter 4.6
• code pieces (trap.c, uart.c, plic.c, console.c)

Lab lazy alloc:

• see lab lazy notes

W4

Prep:

• riscv calling convention
• lec5&6&7

Lab traps:

• see lab traps notes

W3

Prep:

• xv6book Chap3
• kernel/memlayout.h, kernel/vm.c, kernel/kalloc.c, kernel/riscv.h, and kernel/exec.c
• Lec 3&4

Lab pgtbl (Page tables):

• see lab pgtbl notes

W2

Prep：

• pointers in K&R C programming

• chap2, 4.3, 4.4 of xv6 book

• syscall和process相关的源码

Lab syscall:

• 一开始想复杂了 实际上实现trace要做的只是：

  • 给每个process打上"标签" ==>
  • 并把这个标签传递给子进程 ==>
  • 最后在syscall()时根据标签判断是否需要print trace

• 实现syscall：

  • 【准备】完成各种文件里的函数/变量申明
  • sysproc.c中call sysinfo()
  • sysinfo.c中，call nproc() 和freemem()，然后用copyout()把sysinfo拷贝到user处
  • kernel/kalloc.c中实现freemem() ：统计free memory的大小（利用struc run统计N of free page，可以参考函数kalloc()）
  • kernel/proc.c中实现nproc() ：统计进程数量（穷举NPROC并判断struc proc里的state以计数）

W1

Prep work: Read Chapter 1 of http://xv6.dgs.zone/

Lec:

• a text overview
• example materials

Lab Util:

• Useful commands:
  • make qemu: xv6 booting
  • ctrl-a + x: quit qemu
  • make clean: clean production files
  • ctrl-p: print information about each process
  • make grade: local test for all commands
  • ./grade-lab-util someCommandor make GRADEFLAGS=someCommand grade: runs the local tests for a specific command
• Reminder: dont forger to add command to UPROGS in Makefile
• Error fix:
  • [Mac M1] make grade reports env: python: No such file or directory. Solution: ln -s $(which python3) /usr/local/bin/python
  • 对于每个branch，需要在user/sh.c的runcmd函数前添加__attribute__((noreturn))，不然xv6启动会报错

Other Notes

GBD

About How to use GDB https://zhuanlan.zhihu.com/p/354794701

• make qemu-gdb

• in another window && same dir:riscv64-unknown-elf-gdb