In-class notes for 11/04/2020 (CS 273 (OS), Fall 2020)

In-class notes for 11/04/2020

CS 273 (OS), Fall 2020

Project
- Office hours or appointment?
Optional exam Monday - Topics

Deadlock

Definition of deadlock
Four necessary and sufficient conditions for deadlock; resource graphs
- Exercises from last time
Strategies for dealing with deadlock
- Ignoring deadlock
- Detection and recovery
  - Example
- Deadlock avoidance ("safe" states)
  - Example
  - Banker's algorithm
- Deadlock prevention (negating conditions)

Security and protection

Principles of security
- Be educated about security as a user, system administrator, implementer and/or designer.
- Think security throughout design and implementation
- Make security design simple and verifyably correct
- Beware of unsafe assumptions upon which security depends.
- Give the least possible access in every conceivable way.
- Seriously test security
- Security/convenience tradeoff.

Review topics for optional exam

Memory management
- Swapping - copy all memory for a (not currently used) process to disk
- Paging - copy pages of content to/from main memory. Know terms, mechanism, page replacement algorithms
- Segmented memory - hardware feature visible to programmer, where segment number is (possibly implicit) part of address of memory.
- Meta-concepts: fragmentation (internal and external)
Exercise: p254 #36
Programming with sockets, pthreads, FILE library
- Programming with sockets - see sender.c, receiver.c, HW 4
- Programming with pthreads - see pthreads.c, HW 6, HW 7
- Programming with FILE library - see FILE.c, HW 9
Be able to read, modify, answer questions about these codes; be familiar with homework exercises
File systems
- Typical system calls - open(), close(), read(), write(), mkdir(), dup(), lseek(), mount(), etc.
  - Awareness of what these do and that they are FS calls
- Features apparent to the user, with emphasis on those discussed in class
- File storage strategies
  - FAT-32
  - Linux i-node. pseudocode fsck algorithm.
- Block cache: concept, block replacement algorithms, special cases (e.g., doubly indirect blocks, cached i-nodes/directories), sync
- Issues in log-structured file systems and journalling
I/O and devices
- Goals for I/O software: given a list of them, describe what they are and why they are important.
- Which layers of I/O software are used in given operations in a computing system (e.g., HW9)
- Structure of a device driver
Deadlock
- Definition of deadlock
- Four necessary and sufficient conditions for deadlock; resource graphs
- When to consider deadlock strategies discussed in class.
  - Ignoring deadlock
  - Detection and recovery
  - Deadlock avoidance ("safe" states), Banker's algorithm
  - Deadlock prevention (negating conditions)
Any items through today on security

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