Reading 11: File System

Everyone:

Next week, we will descending further down the system stack and introduce system calls, which are services or operations performed by the operating system kernel on our behalf. In particular, we will explore system calls related to I/O, files, and directories and discuss how many of the utilities we use every day are implemented.

Readings¶

The readings for this week are:

1. Operating Systems: Three Easy Pieces

   • Files and Directories

Optional References¶

1. System Programming Wiki

   • Filesystems

2. Linux Programming Interface

   • File I/O: The Universal I/O Model

3. Julia Evans

   

   

   

Quiz¶

This week, the reading is split into two sections: the first part is a dredd quiz, while the second part involves one C program: walk.c.

To test the C program, you will need to download the Makefile and test scripts:

$ git checkout master                 # Make sure we are in master branch
$ git pull --rebase                   # Make sure we are up-to-date with GitHub

$ git checkout -b reading11           # Create reading11 branch and check it out

$ cd reading11                        # Go into reading11 folder

# Download Reading 11 Makefile
$ curl -LO https://raw.githubusercontent.com/nd-cse-20289-sp22/cse-20289-sp22-assignments/master/reading11/Makefile

# Download Reading 11 walk.c
$ curl -LO https://raw.githubusercontent.com/nd-cse-20289-sp22/cse-20289-sp22-assignments/master/reading11/walk.c

# Download, build, and execute tests
$ make test

Questions¶

Record the answers to the following Reading 11 Quiz questions in your reading11 branch:

Programs¶

Given the provided Makefile and walk.c, you are to do the following:

1. Modify Makefile to include a rule for the walk program. Be sure to use the CC and CFLAGS variables in your rule.

   Note: Consider the use of automatic variables.

   Once you have a working Makefile, you should be able to use the make command to run your recipes:

   $ make clean                                  # Remove targets
   rm -f walk
   
   $ make                                        # Build targets
   gcc -Wall -std=gnu99 -g -o walk walk.c
   

2. Modify walk.c so that it uses system calls in C to implement the equivalent Python script:

   import os
   import sys
   
   root = sys.argv[1] if len(sys.argv) > 1 else '.'
   
   for name in os.listdir(root):
       path = os.path.join(root, name)
       if os.path.isfile(path) and not os.path.islink(path):
           print(name, os.path.getsize(path))
   

   That is, given a root command-line argument (default is "." if nothing is specified), the program should iterate through the contents of that root directory and print out the name and size of each regular file.

   Fill in the Blanks¶

   The code has a few ____ placeholders. You will need to replace these placeholders with the appropriate functions and variables to complete the program.

   Here is a list of some possible functions and variables you may wish to use:

   • opendir
   • readdir
   • closedir
   • strerror
   • sprintf
   • stat
   • e->d_type
   • e->d_name
   • s.st_size

Once you have a working walk.c, you should be able to build and run it:

$ ./walk        # No arguments (current directory)
Makefile 446
walk 24864
README.md 13
answers.json 303
test_walk.sh 1824
walk.c 1000

$ ./walk ..     # Parent directory
Makefile 385
README.md 2654
.replit 17
.gitignore 34
Dockerfile 499

Submission¶

To submit you work, follow the same process outlined in Reading 01:

#--------------------------------------------------
# BE SURE TO DO THE PREPARATION STEPS ABOVE
#--------------------------------------------------

$ cd reading11                        # Go into reading11 folder

$ $EDITOR answers.json                # Edit your answers.json file

$ ../.scripts/check.py                # Check reading11 quiz
Checking reading11 quiz ...
     Q01 0.50
     Q02 0.50
     Q03 1.00
   Score 2.00 / 2.00
  Status Success

$ git add answers.json                # Add answers.json to staging area
$ git commit -m "Reading 11: Quiz"    # Commit work

$ $EDITOR walk.c                      # Edit source code

$ make test                           # Build and Run tests
Checking reading11 walk ...
  walk (no arguments)                      ... Success
  walk .                                   ... Success
  walk ..                                  ... Success
  walk ~                                   ... Success
  walk /etc                                ... Success
  walk asdf                                ... Success

    Score 2.00 / 2.00
   Status Success

$ git add Makefile                    # Add Makefile to staging area
$ git add walk.c                      # Add source code to staging area
$ git commit -m "Reading 11: Code"    # Commit work

$ git push -u origin reading11        # Push branch to GitHub