Introduction to Operating Systems

1
Introduction to Operating Systems

• Project 3, Recitation 3
• Fan Wu
• fwu2_at_cse.buffalo.edu
• www.cse.buffalo.edu/fwu2/

2
Problem 3 Addendum

• Recognizing starting and ending point of commands
• Combine all the commands in a single stream
• R_1_1_R_2_2_W_1_2_5_ABCDE_R_1_2_
• Using Start Request T 1 and End Request T 2
  command
• T 1
• R 1 1
• R 2 2
• W 1 2 5 ABCDE
• R 1 2
• T 2

3
Problem 3 Addendum (contd)

• Padding unfilled bytes
• Using \0, or say null character
• W 2 2 5 ABCDE
• ABCDE\0\0\0
• W 2 2 256 ABTRCYNM
• ABTRCYNM

251 \0
256 characters
4
Problem 3 Addendum (contd)

• How to use random generator?
• Include header ltstdlib.ingt
• Initialize
• srand (unsigned int seed)
• Generate a random number in range 0, RAND_MAX
• rand()
• Generate a random number in range a, b
• (int)(((double)rand() / ((double)RAND_MAX
  (double)1)) (double)(b - a 1)) a

5
Dealing with Errors

• Error Could not open file mydisk
• File mydisk has permission ---------- after
  using
• open(mydisk , O_RDWR O_CREAT, 0)
• Solution
• chmod 644 mydisk
• -rw-r--r-- 1 fwu2 csgrad 25600 Nov 10 0549
  mydisk

6
Dealing with Errors

• Error Address already in use
• gtps a
• gtkill process
• Wait 30 seconds
• Try again

7
Problem 4

• The Intelligent disk-storage system IS problem
  3 with the addition of a disk scheduler.
• You are required to implement
• FCFS First Come First Serve
• SSTF Shortest Seek Time First
• C-LOOK go to last requested cylinder from
  current cylinder, then snap back to the lowest
  request cylinder

8
Problem 4 (contd)

• Four ways to call different schedulers
• Open 3 ports on server, the first port to handle
  FCFS, the second port to handle SSTF, and the
  third port to handle C-LOOK
• Pass another command line parameter 1 for FCFS,
  2 for SSTF, 3 for C-LOOK
• Create 3 different disk servers, i.e. compile
  each one separately (Not preferred)
• Pass another parameter from the client program,
  i.e., use "A 1" for FCFS, "A 2" for SSTF, "A 3"
  for C-LOOK. Return 1 if success, or 0 if failure

9
Problem 4 Demo Run

• Server
• ./IDS
• Usage ./IDS ltFilenamegt ltCylindersgt ltSectorsgt
  ltTrackToTrackSleepTime(ms)gt ltcachesizegt
  ltschedulergt
• Scheulers 1 -- FCFS
• 2 -- SSTF
• 3 -- C-LOOK
• ./IDS mydisk 10 10 100000 8 2
• Random data client
• ./DCRD
• usage ./DCRD ltserverAddrgt ltNgt ltRandomSeedgt
• ./DCRD localhost 40 2

10
Problem 4 Demo Scripts

• Server side

Receive I Processing command(s) I Reply 10
10 Receive W 8 0 10 DJKSBPQZHH R 9 3 R 9 8 R 5
5 W 1 3 10 XWICBQUWTY R 1 6 R 7 2 R 0 5 R 9 9 W 9
7 10 YOIUTSRPAT W 6 5 10 NKMSODZIKG R 9 5 R 8 2
W 6 4 10 VYBFQSFQNB Processing command(s)
R W R R R R R W Processing command(s) W R W R R
W W R Processing command(s) R R R W W R R
W Processing command(s) R R W W W R R
W Processing command(s) W R R R R W W W Reply
111AGBLEJBODW1111IHOHFFYVMQ111111111QRPGRJXJYK1XSR
HJUTFLH1111111111111kkkkkkllll1111XSRHJUTFLH11QRPG
RJXJYK1COEPLDJXJI111
11
Problem 4 Demo Scripts

• Client side

Using chars 2 Sending I Client requested
'I' and got back cylinders10 and
sectors10. Client is sending 40 random
requests. Using chars 478 Sending W 8 0 10
DJKSBPQZHH R 9 3 R 9 8 R 5 5 W 1 3 10 XWICBQUWTY
R 1 6 R 7 2 R 0 5 R 9 9 W 9 7 10 YOIUTSRPAT W 6 5
10 NKMSODZIKG R 9 5 R 8 2 W 6 4 10 VYBFQSFQNB
Client recieved the following
responses... 1111111111111111111111111111111111111
111 Executable time for 40 random RW requests is
8067304 microseconds. Exiting Random data
client.
12
Plotting

• MS Word
• Insert --gt Picture --gt Chart
• Latex
• Gnuplot
• http//www.gnuplot.info/
• Matlab

13
Problem 5 File System Server
Basic / Intelligent Disk Server
server
client
File System Server
Test Client
server
client
14
Problem 5 File Allocation Table
N lt Cylinder Sector
15
Problem 5 Command Types

• Commands that do not need disk operation
• F, C, D, L
• Commands that need disk operation
• R, W, A

16
Problem 5 Demo Run

• Server
• ./BDS mydisk 10 10 100000
• ./FS
• Usage ./FS ltDiskServerAddressgt
• ./FS localhost
• Client
• ./FC
• Usage ./FC ltServerAddrgt
• ./FC localhost

• F
• C file1
• C file2
• L 0
• W file1 5 ABCDE
• A file2 6 FGHIJK
• L 1
• R file2
• D file1
• L 1
• exit