CS439: Principles of Computer Systems

Discussion Section 9 Problem Set

Due in Section on Friday, April 19, 2024

The problem set must be completed before section and brought to section. To ensure that your problem set is turned in correctly and that you receive credit for discussion section, you must follow these guidelines exactly.

Include the following header at the top of your file:

Discussion Section Problem Set #:
Student Name:
EID:
If I had to talk like an animal, I would pick...


Partner Name:
EID:
If I had to talk like an animal, I would pick...

You may either type your answers or write them by hand, but you must bring a hard copy to discussion section.

In discussion section, your TA will check that you worked with your partner, you made a good effort on the problem set, you are participating in the discussions in section, and you are ready and able to answer when called upon. If all of those are true, you will receive credit for discussion section that day. Note that a "good effort" on the problem set includes that all answers are in words unique to you and your partner and not copied from anywhere else, including the slide deck.

In some operating systems, I/O from/to disk is done directly to/from a buffer in the user program's memory. The user program does a system call specifying the address and length of the buffer (the length must be a multiple of the disk record size).
The disk controller needs a physical memory address not a virtual address. Your co-worker proposes that when the user does a write system call, the operating system should check that the user's virtual address is valid, translate it into a physical address, and pass that address and the length (also checked for validity) to the disk hardware.
This won't quite work. In no more than two sentences, what did your co-worker forget?
Explain the steps that an operating system goes through when the CPU receives an interrupt.
In class, we covered the idea of remote procedure calls. Name four difficulties that may be encountered when one attempts to implement a remote procedure call.

There are additional complications when the procedure executes a system call. What are the complications and how might you fix them?
Adapted from Tanenbaum page 607.
In two-phase commit, suppose the master fails after writing ``GLOBAL_COMMIT'' to disk and sending ``GLOBAL_COMMIT'' to all participating nodes but before any of the nodes receive this message. Suppose that the ``GLOBAL_COMMIT'' message reaches i of the n participants and that the participants implement a protocol in which they communicate with one another when they suspect the primary has died. What is the minimum number of participants that must receive the ``GLOBAL_COMMIT'' message to allow the participants to complete the transaction without waiting for the master to recover?
Sun's network file system (NFS) protocol provides reliability via:
- at-most-once semantics
- at-least-once semantics
- two-phase commit
- transactions
In class, we have discussed many methods to get reliability from unreliable parts. Name and describe two.