system-programming/chp4/README.md

Chapter 4 – Advanced File I/O

File Metadata and the stat Family

• Use stat(), fstat(), lstat() to retrieve file metadata:
  • File type, size, inode number, permissions, ownership, timestamps (atime, mtime, ctime).
• The stat structure includes all these details.

File Types

• Regular file, directory, symbolic link, character/block device, FIFO, socket.
• Use macros like S_ISREG(), S_ISDIR() to test file types.

File Permissions and Modes

• Represented by 12 bits (e.g., rwxr-xr--), plus sticky/SUID/SGID bits.
• Manipulate with chmod(), fchmod(), umask().
• Ownership changed with chown() and fchown().

Links

• Hard links: multiple filenames point to the same inode.
• Symbolic links: separate files that reference other paths; can be broken.
• Use link(), unlink(), symlink(), readlink().

Directories

• Open with opendir(), read entries with readdir().
• Low-level: getdents() system call.

File Timestamps

• utime(), utimes(), futimens(), and utimensat() to update access/modification times.

File Descriptors and Flags

• Manipulate with fcntl():
  • Set non-blocking mode (O_NONBLOCK), FD_CLOEXEC flag, file locks.
  • Duplicate with dup() and dup2().

File Locking

• flock() for advisory locking (whole file).
• fcntl() for POSIX record locking (ranges).

Temporary Files

• tmpfile(), mkstemp() are safe methods to create temp files.

Summary

• Chapter 3 focuses on extended file handling: metadata, links, directories, file modes, and advanced descriptor manipulation.