Homework answers / question archive / CEG4350/CEG6350 - Operating Systems P2: Subdirectories, and Moving Files The project for the current term is to implement (on a simulated disk) a file system based on the design explored in the lectures

CEG4350/CEG6350 - Operating Systems P2: Subdirectories, and Moving Files The project for the current term is to implement (on a simulated disk) a file system based on the design explored in the lectures

Computer Science

Share With

---

CEG4350/CEG6350 - Operating Systems

P2: Subdirectories, and Moving Files

The project for the current term is to implement (on a simulated disk) a file system based on the design explored in the lectures.  This project is divided into four pieces.   You must read and follow the Project Expectations.  Study the grading sheet given below.

This is Part 0 of the project for this term.  You are expected to study and modify the source code files given in source.tbz and achieve the functionality described below.  Do not use source code files of others or even those of mine but from prior terms. 

Be Considerate. Do make sure that you are not using up too much space (say > 10 MB) in your home directory.  The following will show your disk space usage:  du -s ~

1. Studying a Program

By the time P2 is due, we would have covered the essentials of our File Sys project. The tar ball source.tbz is a collection of files given so that (i) you can get started quickly with our project, and (ii) you can see the style of how larger systems programs are written. Download source.tbz from the link above.  In the OSIS Lab, it can be un-tar-ed as follows:  tar xvvfj source.tbz

The functionality of  source.tbz  is described in What Is Given. Some details of the code are/were explained in the lectures and in ReadMe.txt. Study the provided source code so thoroughly that you could have written it. Then, answer the itemized questions below in a file named answers.txt.

1. The following are standard library routines:
   fopen, fclose, fread, fwrite, fstat, fscanf, fprintf, sprintf
   Look up their functionality in both the Stevens' book and the on-line man pages.  Describe their functionality briefly, one sentence each, in your own words.
2. List the names of 5 standard library routines other than the above, and 5 system calls used by the code of P2.
3. In the file simDisk.C, what is the point in verifying that statBuf.st_size == nSectorsPerDisk * nBytesPerSector?
4. Study the Notes on Programming in C, by Rob Pike.  All of it is "very" applicable to C++ also.   For five identifiers used in the given source code, (i) either suggest better alternate names and defend why they are better, or (ii) explain why you are comfortable with the names as-they-are.
5. Write the pre- post conditions for
   uint FileVolume::read33file(byte *fs33leaf, byte *unixFilePath)
uint FileVolume::write33file(byte *unixFilePath, byte *fs33leaf)

2. Learn to Use GDB

Coming into the course, you are expected to be comfortable with gdb. Debugging large programs requires the construction of (extra) observer methods. Using gdb or some other debugger is not as effective as invoking observers and studying their output in a peaceful place ("under a tree"). Nevertheless, gdb can be useful as a last resort, and you must be able to use it well.

1. Start script. Make P2 as given. Run our program P2 through gdb.
2. Set a breakpoint at immediately after setArgsGiven(buf, arg, types, nMax);  Examine the values of buf, arg, types, nMax.
3. Type in a command to our shell to make a file volume. Trace the execution from the above breakpoint onwards by single stepping until after simDisk is initialized in mkSimDisk().
4. Set a breakpoint at the bottom of the SimDisk constructor. Examine the value of  diskName.
5. Type in a wrdisk request followed by a rddisk.  Verify that the results match.
6. End the script.  Turn in this script as a file named gdbSession.txt

3. Additions and Improvements

Part of large program development is independently, but wisely, deciding what to do for certain "erroneous" situations. Should we ask the professor for what to do for every possible error you can think of? [Answer: No. You think about it. You take a reasonable action. You document this in your source code, and in ReadMe.txt. And, be ready to defend your choice should it be questioned.]  Should SimDisk() constructor printf or cout>> an error message? [No.] When does/should mkSimDisk() return a zero? [Think.]  Remember that one of the goals of CEG 433/633 is to make you think about larger programs. Part of this is to supply missing, but needed, details in the problem description.

3.0 What Is Given

As given, the files of source.tbz implement the following. 

fs33% mkfs disknm

creates an initially empty file volume on the simulated disk named disknm.dsk.  The maxfnm, the number of i-nodes, and the i-node height are all given in the diskparams.dat file corresponding to the line for disknm.  The file volume so constructed is the current file volume as used below.    The height does include the fileSize field.  If disknm.dsk is not already created, do so now.

The names of 433-files are at most maxfnm characters long.  Valid characters in file names are a-z, A-Z, 0-9, hyphen (minus), and period ('.'); all other characters (spaces, slashes, control characters, etc.) are illegal.  maxfnm is given in diskparams.dat.

Here is an example diskparams.dat. Lines starting with # are comments.   For clarity, I have lined-up the columns, but the actual diskparams.dat may not do so.

# diskName nBlocks nBytesPerSector maxFnm nInodes iNodeHt
D1             128             512      8      20       3
D2            1024             256     16     100       8

fs33% cp @P0/test0.cpp myfile.txt

copies P0/test0.cpp from your Linux (indicated by the @ sign) current working directory to the current (for now, root) directory of the current file volume, as a file named myfile.txt  and prints to stdout the i-node number of  myfile.txt.  If  myfile.txt already exists, the new content silently replaces it.  (In the cp commands, we need to simultaneously deal with path names of files in 433-file-volume and Linux.  Only in such cases,  the latter are prefixed with the @ symbol.)

fs33% cp myfile.txt @P0/test1.cpp

copies myfile.txt of the current file volume to P0/test1.cpp of your Linux current directory and prints to stdout the i-node number of  myfile.txt.  If P0/test1.cpp already exists, it is silently replaced. 

fs33% cp myfile.txt file2.txt

copies myfile.txt of the current file volume to file2.txt of the current volume and prints to stdout the i-node number of file2.txt.  If  file2.txt already exists, the new content replaces it.

fs33% ls

prints a listing, much like the Unix ls -lisa, of all the files in the root directory of the current file volume.

fs33% rm myfile.txt

remove the file named myfile.txt from the root directory and prints to stdout the i-node number that  myfile.txt  had.   If the file named myfile.txt does not exist, be quiet and print  0.

fs33% inode 4

prints the contents of i-node numbered 4,  if it exists, of the current file volume.

Here is a stdTestScriptP2.txt.  Use it as in ./P2 < stdTestScriptP2.txt with the above diskparams.dat as well as with this one.

3.1 Improvements

You will find that P2, as given, is "functional" but fragile (not robust).  Improve it so that it is crash-proof no matter what inputs are given. Describe the changes you made in a file named improvements.txt.  In later project phases, we (you and I) will replace invocations of TODO by working code.

3.2 Nested Directories

This P2 deals with only one file volume at a time.  No mounting is involved.  Thus, we have only one file volume to deal with at any time.  Our goal in this part of the project is to add hierarchical directories.  Our shell should now have mkdir, rmdir and chdir commands.  It must, of course, have a single anonymous directory that is the root.

3.3 Moving Files

Unix command mv does two things: (i) when the last argument given is a directory already existing, it moves the files or directories given in the rest of the arguments from where they are into this target directory, or (ii) renames the first argument file or directory into the second argument.  Look up the man page for more details.

3.4 A Simple Test Session

Only the additional elements compared to the given P2 are described below.   Add these appropriately to the test script.  Our path name syntax is the same as Unix path names.   Obviously, not every arbitrary string is a valid path or name.  Also, the dot and the dot-dot are not permissible as arguments in some contexts below.  Nevertheless these commands must be robust.   In the following, all meta-variable names that end in pnm are pathnames that are either relative to the current directory or are full/absolute pathnames.

fs33% mkdir dnm

creates a new empty directory named dnm in the current directory, and prints its i-node number.  If a file or directory named dnm already exists in the current directory, it creates nothing new and returns 0.  The i-node now needs to have a field that indicates that it is or is not a directory.  Assume that dnm does not contain slashes.

fs33% rmdir dnm

If the directory dnm is empty, deletes it.  If dnm is non-empty, no change is made in the file system. In either case, it prints the number of directory entries in dnm (not counting the dot and dot-dot).

fs33% mv da db

The da is either a normal file or a directory. If da does not exist, return 0 and nothing is altered in the file volume.  If db does not exist in the current directory, da is renamed as db.  If db is an existing directory  in the current directory, the da is moved (along with all its contents) inside db as a subdirectory of db.  If db is an existing but ordinary file, return 0. Carefully consider if da and db can be pathnames.

fs33% chdir pnm

changes the current directory to pnm.   If it begins with slash, it is an absolute path name. and the new current directory is pnm.  If pnm does not begin with a slash, the new current directory is pnm relative to the present current directory.  In either case, print the absolute full path name of the new current directory.   Current directory is initially established as the root of a newly created/ found file volume.

fs33% pwd

prints the full path name of current directory.  

fs33% ls pnm

prints the contents of directory pnm in the "long" format as in Unix ls -l.

fs33% inode myfile.txt

is an overload of the above command.  It first discovers the i-number of file myfile.txt  located in the current directory of the current volume and then invokes the inode command above.

4. Turn In

All projects need to be submitted via Pilot.  

---

Grading Sheet for  CEG 4350/6350: Operating Systems P2: Subdirectories, and Moving Files Instructor = Thomas Wischgoll;

Extra credit points are awarded in recognition of good work and extra work, in addition to the max possible points.  Quality is subjectively judged.  Merely turning in a file will not receive full score.  Some items have a cascading effect.

Student

OSIS Login ID

Extra credit

Points

Item description	Max	Points
ReadMe.txt exists with content as described in Project Expectations	5
Your testscript.txt is designed so that all the functionality is demonstrated, including robustness.	5
Your program successfully navigates your own testscript.txt.  ( If yours is too simple, we may run it through our script that you will get to see only after the due date.)	5
answers.txt	5
gdbSession.txt	10
Improvement	5
mkdir dnm	10
chdir pnm	10
rmdir dnm	10
ls dnm	10
mv da db (db may not exist, but if it does, it is an ordinary file)	5
mv da db (db exists, and is a directory; da may or may not exist inside db)	5
mv da db (both are path names)	5
pwd	5
inode printing for both i-numbers and file names	5
Bonus points 25, if you implement rm -fr directory-name (Look up: man rm)	B25
Bonus points 25, if you implement ls -lR directory-name (Look up: man ls)	B25
Files were not submitted using pilot = minus 10 points	-10
Total	100