Agenda

<aside> 📌 Reminders

• Last tutorial
• Next week’s tutorial replaced with help session
• P4 due April 6, 2025
• Final exam April 17, 2025 </aside>

🔺 Directories

A directory is a special type of file that acts as a container for other files and subdirectories, forming the hierarchical structure of the filesystem.

Just like regular files, directories are represented internally with iNodes (with the usual metadata), but, unlike regular files, directories don’t store content in their data blocks. Instead, they function as lookup tables that map filenames to their corresponding inodes. When you list the contents of a directory (ls), the system retrieves the filenames stored in that directory and then uses the inode numbers to access metadata and file locations.

Source: https://unix.stackexchange.com/questions/325294/how-does-a-directory-inode-keep-its-file-list

So, adding or removing a file to/from a directory amounts to just writing or erasing an entry in its corresponding data block.

Key Characteristics of Directories:

• Stored as Files: In Unix, directories are implemented as files that contain a list of filename-inode pairs.
• Hierarchical Organization: Directories can contain other directories, forming a tree-like structure.
  • The root directory (/) is the root of the tree.
  • Directories form the internal nodes of the tree
  • Files form the leaves of the tree

• Special Entries (. and ..): Every directory includes:
  • . (a reference to itself)
  • .. (a reference to its parent directory)
• Access via System Calls: The OS provides system calls like opendir(), readdir(), and isdir() for interacting with directories programmatically.

🛣️ File paths

Paths to files/directories can be relative or absolute.

• Absolute paths: These specify the entire location of a file from the root directory; can be viewed as a path starting at the root of the filesystem tree and terminating at the file

The absolute path /foo/foo.txt

• Relative paths: These specify the location of a file or directory relative to the current working directory (more on working directories below). Instead of starting from the root (/), a relative path begins from the directory you are currently in.

The relative path foo/foo.txt ; relative to the root directory

Special Notation for Relative Paths: