Minimal Linux File System Manager written in C

Implementation

Day 1

• Implemented basic functions (init, touch, mkdir)
• Used while(1) and fgets to obtain data
• Used strtok to store command arguments in a char*
• Implemented 'ls' and 'stop' commands

Day 2

• Implemented rm, rmdir, and pwd operations
• Encountered most obstacles on this day
• Deletion operations generated many errors due to traversing head_children_files and head_children_dirs lists
• Spent several hours debugging
• Used valgrind and GDB (Valgrind reported the most errors)

Main Idea

The designed program follows this hierarchy:

                 ....             ........
                  ^                ^   ^
                   \               |  /
                   d1_1 d2_1      f3_1
                     ^  ^         ^
                      \ |        /
                       d1   d2  d3   f1  f2
                        ^    ^   ^   ^   ^
                         \   |   |   |  /
                           home(directory)

Represented as:

                   |d1_1   
                |d1|d2_1
            home|d2
                |d3|f3_1
                |f1
                |f2

Data Structure Meanings

struct Dir

• next: Move to the neighboring directory
• head_children_dirs: First element in the list of subdirectories
• parent: Parent of subdirectories (home directory is the root)

Example:

• In directory d1_1:
  • d1_1->next leads to d2_1
  • d1_1->parent is d1
  • d1->head_children_dirs is d1_1

struct File

• next: Move to the neighboring file
• parent: Parent of files in the current directory

Example:

• When pwd returns /home:
  • f1->parent is home
  • f1->next is f2

Implementation Details

touch and mkdir

• Created create_condition function to check for file/directory existence
• search traverses file list, find traverses subdirectory list
• Returns 1 only if file/directory not found in lists
• Allocates memory and adds to end of respective list using while() traversal

ls

• Displays subdirectories list first, then files list
• Uses aux1_helper for subdirectories and aux2_helper for files
• Checks for end of lists with if(...!=NULL)

cd

• Verifies existence of target directory
• Uses sequences *target = find or *target = (*target)->head_children_dirs
• For "..", changes current directory to its parent

stop

• Uses recursion to deallocate memory
• Takes root of hierarchy (home directory) as argument
• aux1_helper frees memory for file list in a subdirectory
• aux2_helper uses recursion to traverse subdirectories

rm and rmdir

• Traverses respective lists to find and delete items
• rmdir calls stop function if directory contains subdirectories/files

pwd

• Uses helper variable to build path string
• Traverses up to root, concatenating directory names

tree

• Implemented recursively
• Uses aux_iterator to move towards last-level subdirectory
• Displays tree form using printf("%*s\n",4*level+strlen(string),string)

mv

• Checks conditions: oldname must exist, newname must not
• Moves file/directory to end of list under specified conditions
• Handles all cases: item at beginning, middle, or end of list

Main Function

• Uses fgets to read input line
• Uses strtok to obtain command arguments
• Uses strcspn to handle newline character from fgets
• Implements command execution in a while(1) loop
• Program ends on 'stop' command