Paper Review Questions - OS Structures

Question 1

SPIN Paper

What features of Modula-3 are essential for implementing the extensibility features of SPIN? Why?

Answer 1

TODO

Question 2

SPIN Paper

Strand is an abstraction provided by SPIN for processor scheduling. Explain what this means. In particular, how will a library OS use the strand abstraction to achieve its desired
functionality
with respect to processor scheduling?
[Hint: Think of the data structures to be associated by the
the library OS with a strand.]

Answer 2

TODO

Question 3

SPIN Paper

How can SPIN ensure that a given library OS does not become a CPU hog, shutting out other library OSes?
[Hint: Think of how SPIN can control “macro” resource allocation
at start up time for a library OS.]

Answer 3

TODO

Question 4

SPIN Paper

How can SPIN ensure that a given library OS does not become a physical memory hog, shutting out other library OSes?
[Hint: Think of how SPIN can control “macro” resource allocation
at start up time for a library OS.]

Answer 4

TODO

Question 5

Exokernel paper

A library OS implements a paged virtual memory on top of Exokernel. An application running in this OS encounters a page fault.

Walk through the steps from the time the page fault occurs to the resumption of this application.

Make any reasonable assumptions to complete this exercise (stating the assumptions).

Answer 5

TODO

Question 6

Exokernel paper

“The high level goals of SPIN and Exokernel are the same.” Explain why this statement is true.

Answer 6

TODO

Question 7

Exokernel paper

Map the mechanisms in Exokernel to corresponding mechanisms in SPIN.

Answer 7

TODO

Question 8

Exokernel paper

Explain how the mechanisms in Exokernel help to meet the high level
goals.

Answer 8

TODO

Question 9

Exokernel paper

Explain how the mechanisms in SPIN help to meet the high level
goals.

Answer 9

TODO

Question 10

Liedtke paper

Sketch how you will implement a device driver (say for a simple device like a keyboard; if you are really adventurous do for a disk) using the primitives provided by Liedtke’s microkernel. [Hint: Assume address space A0 magically exists that exposes the
physical memory. Assume the device registers are memory mapped at some well known physical addresses in high memory.]

Answer 10

TODO

Question 11

Liedtke paper

What is the difference between a “thread” as defined in Liedtke’s paper and a Strand in SPIN?

Answer 11

TODO

Question 12

Liedtke paper

Liedtke argues that a microkernel should fully exploit whatever the architecture gives to get a performance-conscious implementation of the microkernel. With this argument as the backdrop, explain how
context switching overhead of a microkernel may be mitigated in modern architectures. Specifically, discuss the difference in approaches to solving this problem for the PowerPC and Intel Pentium architectures. Clearly explain the architectural difference between the two that warrant the difference in the microkernel implementation approaches.

Answer 12

TODO

Question 13

Liedtke paper

Explain the notions of “independence” and “integrity” in the L3 microkernel.

Answer 13

TODO

Question 14

Liedtke paper

All the subsystems in L3 live in user space. Every such subsystem has its own address space. The address space mechanism “grant” allows an address space to give a physical memory page frame to a peer subsystem. Can this compromise the “integrity” of a subsystem? Explain why or why not.

Answer 14

TODO

Question 15

Liedtke paper

“Trust in the L3 microkernel is transitive.” Explain what this sentence means.

Answer 15

TODO

Question 16

Xen paper

Imagine a Linux OS top of Xen (XenoLinux). A user launches an application “foo” on top of XenoLinux. Walk through the steps that happen actually starts running.

Answer 16

TODO

Question 17

Xen paper

foo starts executing; it executes a blocking system call:

fd = fopen(“bar”);

(a) Show all the interactions between XenoLinux and Xen for Clearly indicate when foo resumes execution.

Upon resumption, foo executes another blocking system call:

fwrite(fd, bufsize, buffer);

(b) Show all the interactions between XenoLinux and Xen for Clearly indicate when foo resumes execution.

Don’t worry about the exact syntax of the above calls.

Answer 17

TODO

Question 18

Xen paper

Construct and analyze a similar example for network transmission and reception by foo.

Answer 18

TODO

Question 19

Xen paper

All processes in XenoLinux occupy the virtual address space 0 through VMMAX, where VMMAX is some system defined limit of virtual memory per process. XenoLinux itself is a protection domain on top of Xen and contains all the processes that run on top of it. Given this how does XenoLinux provide protection of processes from one another? [Hint: Work out the details of how the virtual address spaces of the processes are mapped by XenoLinux via Xen.]

Answer 19

TODO

Question 20

Xen paper

Give three important motivations for OS virtualization.

Answer 20

TODO

Question 21

VMWare ESX

What is the difference between VMWare workstation and VMware ESX server? Discuss how OS calls from a user process running inside a VM are handled in the two cases.

Answer 21

TODO

Question 22

VMWare ESX

Discuss the difference in memory virtualization in VMware and Xen.

Answer 22

TODO

Question 23

VMWare ESX

What are the approaches to reclaiming memory in a virtualized over-subscribed server? Discuss the pros and cons of each approach.

Answer 23

TODO

Question 24

VMWare ESX

Describe how ballooning may be used with Xen.

Answer 24

TODO

Question 25

VMWare ESX

Explain how page sharing works in VMWare.

Answer 25

TODO

Question 26

VMWare ESX

Explain the allocation policy of VMWare.

Answer 26

TODO

Question 27

Microkernel based OS will always be less efficient compared to Monolithic kernel. True or False? Explain your answer in detail.

Answer 27

TODO

Question 28

To what extent has the idea of configurable system services ({\it a la} SPIN and Exokernel) influenced commercial operating systems? (Note: For the sake of this question, any flavor of Unix and Microsoft
Windows fall under commercial OS).

You have to clearly explain how they have been or have not been influential, and back such statements with facts and reasons.

Answer 28

TODO