CS140 Operating Systems and Systems Programming Final Exam March 17, 2005 Name: (please print)______________________________ In recognition of and in the spirit of the Stanford University Honor Code, I certify that I will neither give nor receive unpermitted aid on this exam. Signature:_______________________________________ This examination is closed notes and closed book. You may not collaborate in any manner on this exam. You have 180 minutes (3 hours) to complete the exam. Before starting, please check to make sure that you have all 16 pages. 1 12 2 13 3 14 4 15 5 6 7 8 9 10 11 Total Name:_______________CS140 Final Winter 2005 Name____________________ Page 2 of 16f (1) (8 points) Explain why the speed at which a CPU can raise exceptions and return from exceptions could factor into the overheads seen by a virtual machine monitor.CS140 Final Winter 2005 Name____________________ Page 3 of 16f (2) (12 points) Assume you are given an operating system environment with a workload running on it, a list of physical addresses, and a virtual machine monitor capable of running the operating system environment. Explain how you could modify the virtual machine monitor to record the program counter addresses that wrote into any of the physical addresses on the list.CS140 Final Winter 2005 Name____________________ Page 4 of 16f (3) (10 points) If you wanted to implement a spoiler/denial of service attack against a machine over a local area network, would you use UDP or TCP? Justify your answer.CS140 Final Winter 2005 Name____________________ Page 5 of 16f (4) (10 points) Would going from a stop-and-go protocol to one that uses a sliding window likely increase or decrease the number of acknowledgement packets sent for a network session consisting of sending a large file. Justify your answer.CS140 Final Winter 2005 Name____________________ Page 6 of 16f (5) (8 points) Explain how a machine determines the destination Ethernet address based on the destination IP address.CS140 Final Winter 2005 Name____________________ Page 7 of 16f (6) (10 points) Explain why the end-to-end argument might suggest that adding useful security features such as encryption to the link-level layer might not be such a good idea.CS140 Final Winter 2005 Name____________________ Page 8 of 16f (7) (10 points) (a) Would a BSD file system ever put two files created in the same directory in two different cylinder groups? (b) Would a BSD file system ever put files created in different directories in the same cylinder group? Justify your answer. If possible, indicate what would the user of the file system have to do to make it happen.CS140 Final Winter 2005 Name____________________ Page 9 of 16f (8) (10 points) Your Pintos partner decided to add write ahead logging to your file system. He asked you if the log should be in the beginning, middle, or end of the disk. What do you think? Justify your answer.CS140 Final Winter 2005 Name____________________ Page 10 of 16f (9) (10 points) A recently published paper reports an attack on the popular message digest algorithm SHA1 that some people believe may lead to SHA1 being broken. What does it mean for a message digest algorithm to be broken? What bad things can happen?CS140 Final Winter 2005 Name____________________ Page 11 of 16f (10) (12 points) Assume that you are given a file system that used capabilities to protect access to files. Describe an algorithm you could use to convert it into using access control lists. The access control lists should give the users the same access to files as with capabilities.CS140 Final Winter 2005 Name____________________ Page 12 of 16f (11) (10 points) Assume that you know that exactly one bit of a file system’s free block bitmap is incorrect but you do not know which bit that is. Describe an algorithm for computing which bit is incorrect.CS140 Final Winter 2005 Name____________________ Page 13 of 16f (12) (10 points) (a) What units would you use if you were asked to measure the latency of a file system? (b) How about the units for a measure of bandwidth?CS140 Final Winter 2005 Name____________________ Page 14 of 16f (13) (10 points) Explain why in a Unix file system deleting a hard link to a file would require updating the file’s inode while deleting a soft link would not.CS140 Final Winter 2005 Name____________________ Page 15 of 16f (14) (10 points) Would an extent based file system or a linked-file file system allow you to use a greater fraction of the capacity of a disk for a workload of small files? (b) How about big files? Justify your answer.CS140 Final Winter 2005 Name____________________ Page 16 of 16f (15) (10 points) For each of the following attributes of a disk, give the ordering of them (e.g. X <= Y < Z < Q): # of heads # of cylinders # of sectors # of platters # of tracks per platter # of bytes of
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