课程名称︰作业系统
课程性质︰必修
课程教师︰薛智文
开课学院：电资学院
开课系所︰资工系
考试日期（年月日）︰104.6.22
考试时限（分钟）：180
试题 :
Total points: 120
1.[10%] Please describe the problems delivering symmetric key out-of-band.[5%]
Does asymmetric key solve the same problem? Why?[5%]
2.[10%] What is a capability in a protection domain? [5%] What problems if a
capability list is directly accessible to a process executinging that
domain? [5%]
3.[10%] When implementing blocking I/O in a kernel module, it is common to
establish a shared data buffer between kernel threads and user processes.
Please describe how we can use wait_event(queue,,condition) to ensure the
correct behavior even if there are no data available in the buffer.[5%]
In what scenario, is wait_event_interruptible and wait_event_timeout
preferable than wait_event respectively? [5%] Hint: use project 2 as an
example.
4.[10%] When implementing an I/O application, we usually experiment in
higher (application) level for flexibility and avoiding system crash,
then move into lower(kernel, driver or even hardware) level for better
performance. In what scenaraio, we would stay in higher level for better
performance [5%] and lower level for flexibility?
5.Describe utility storage and its advantages?[5%] Describe a real
application of utility storage and its disadvantages using utility storage?
[5%]
6.[20%] Memory management and (disk) storage management use similar
technologies.
a. List 3 common ones.[1,2,2%]
b. Describe 3 technologies which are better used in memory management
but not in storage management, with reasons.
7. [20%] In Project 2, we need to guarantee the following orders.
● The slave program will be executed only after both device modules
have been loaded
● The master program will be executed only after the master device
module has been loaded
● In the slave program, it first set the IP address and then begin
reading data from the slave device with blocking I/O.
a. What happens if the orders are not guaranteed, respectively? [5%]
In what situation, it would be beneficial not guartanteeing the orders
or the orders are not independent? [5%]
b. Please describe the performance differences of different file sizes,
buffer sizes, and implementations (synchronous or asynchronous, ...)[10%]
8. [20%] For a multiprogramming system with many process, when a process need
I/O operation, it will send a system call to the operating system, but if
the controller is busy, the process will be placed in the disk queue,
allowing the operating system to choose. There are some common disk
scheduling algorithms: FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK
a. Suppose there is the total of 200 cylinders on the disk, if it requests
continuous read and write 110, 60, 120, 131, 70, 111, 130. Try to find
which scheduling's disk arm moves the least distance? (Head start on
90th track, the default direction is the direction of increasing)[7%]
b. When the operating system reads the track ,evenly distributed, try to
analyze the performance of SCAN and SSTF? [4%]
c. What application is mostly suitable using FCFS, SSTF, C-LOOK,
respectively? Why?[3*3%]
9. [10%] In this big data era, we sometimes still need to do a snapshot for
our data, which is big and might be stored distributedly anywhere. Provide
your solution optimized for efficiency and describe its disadvantages.