🗂️ File System — Operating Systems Fundamentals

Mini-project of Fundamentos de Sistemas de Operação (Operating Systems Fundamentals), Computer Science degree at NOVA School of Science and Technology (FCT NOVA).

About

A small UNIX-like file system stored on a simulated disk (a regular file split into 2 KB blocks). The disk has a superblock, a bitmap of free blocks, an inode table and data blocks holding file contents and directories. A shell (fso-sh) lets you explore a disk image.

The course provided the disk driver, the bitmap, the shell and the on-disk structures. Our job was to complete the file system in fs.c:

• Path resolution — walk directories from the root inode to find the inode of a path like /dir1/file2
• ls — list a directory's entries with their inode number, type and size
• open, close and read — an open-file table and reading a file's contents through its 11 direct block indexes and one indirect index block

Running it

Needs a C compiler and make (Linux or macOS).

make
./fso-sh small.dsk

fso-sh> ls
listing dir / (inode 0):
ino:type bytes name
  1:D      128 dir1
  2:F      530 file1
  5:F     5562 file2
fso-sh> ls /dir1
listing dir /dir1 (inode 1):
ino:type bytes name
  3:D        0 dir1.1
  4:F      273 file2
fso-sh> copyout /file2 file2.txt
fso-sh> debug        ← superblock, block bitmap and inodes in use
fso-sh> exit

Other commands: cat <path>, help.

What I learned

• How a file system lays out its data on disk: superblock, free-block bitmap, inodes and directory entries
• Mapping a byte offset in a file to a disk block through direct and indirect indexes
• Low-level C: packed structures, raw block I/O and careful buffer handling

Credits

• Miguel Carmo (@MCCProgrammer)
• Tomás Ramos Alves (@Alvesss04)

fso-sh.c, disk.c/disk.h, bitmap.c/bitmap.h, fs.h, the Makefile and the small.dsk disk image were provided by the FSO teaching staff; fs.c was completed by us.

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_{The assignment statement is not included in this repository, as it belongs to the course's teaching staff. This is a student project shared for portfolio purposes.}