In-class notes for 08/28/2020 (CS 273 (OS), Fall 2020)

In-class notes for 08/28/2020

CS 273 (OS), Fall 2020

Upcoming homework assignment HW2, due Monday "midnight"
- For full credit, submit at least part on time, then complete the rest within a week.
- Environment variables - access using third argument of main()
First project will be due on September 21 (see below)

Submitted questions on assignments and technology

More file-related system calls

dup(), pipe(), etc.
- Each process has a kernel file descriptor array, with file descriptor as index and pointer to open-file data structures as values.
System calls for file systems, i.e., OS components that contain files and directories

mount(), umount(), etc.

Devices
- ioctl(), for setting parameters for an I/O (input-output) device (will return for code illustration)
- Berkeley socket calls, for network I/O (will return later)
- Specialized device calls, e.g., time-related calls for interacting with clock device (will return)
Memory management
- brk(), sbrk(), for adjusting how much main memory is allocated to a process.
Process management system calls
- fork(), execve(), exit(), wait(), waitpid()
- Example code: ~rab/os/egs/forkeg.c
  
  (fork(), execve(), and wait() implement the key ideas in the Linux strategy for starting new programs.)
- zombie process -- process called exit(), but its parent hasn't called wait() for it to collect its exit status, so that exited process continues to take up OS resources.

Inclass examples:

Basic idea
Project assignment page
- Report (overview, system calls, known bugs, 1-2 pg experiences)
- Extra features that use system calls. E.g., redirect output, pipe, cd; path search counts (use execve() system call)
Strategy for developing a shell
- Lab2 on parsing -- step 1 in strategy

We now know enough to announce the first project -- to write a Linux shell using system calls. Project assignment page
Will discuss this project later, but you can start now if you want. Be sure to see the strategy recommendations for incrementally developing your shell.

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