VSFS is a block-based filesystem designed for teaching systems programming and operating systems concepts. It uses a fixed disk layout, write-ahead journaling, and a validator to maintain consistency.
The filesystem operates on a virtual disk image with a fixed architecture.
The disk consists of 85 blocks, each 4096 bytes in size.
- Superblock (Block 0): Stores the filesystem magic number (
0x56534653), block size (4096), and offsets for all other regions. - Journal (Blocks 1-16): A dedicated region for storing transaction logs to ensure atomic metadata updates.
- Inode Bitmap (Block 17): Tracks the allocation status of the 64 available inodes.
- Data Bitmap (Block 18): Tracks the allocation status of the 64 available data blocks.
- Inode Table (Blocks 19-20): Stores inode structures, each 128 bytes in size.
- Data Region (Blocks 21-84): Stores the actual file content and directory entries.
- Inodes: Contain type information (file vs. directory), link counts, size, and 8 direct pointers to data blocks.
- Directory Entries: Each entry is 32 bytes, consisting of a 4-byte inode number and a 28-byte null-terminated name.
To prevent filesystem corruption, VSFS implements a journaling system.
- Transaction Records: Metadata changes are written as data records (
REC_DATA) followed by a commit record (REC_COMMIT). - Atomicity: Updates to the inode bitmap, inode table, and directory blocks are first staged in the journal.
- Recovery: The
installcommand replays committed transactions from the journal to the permanent data region.
The project includes a robust validation tool to ensure disk consistency.
- Superblock Check: Verifies magic numbers and internal offsets.
- Bitmap Verification: Cross-references the inode and data bitmaps against actual usage in the inode table and directory structures.
- Directory Integrity: Ensures that all directories contain valid
.and..entries and that link counts are accurate. - Pointer Safety: Detects out-of-range block pointers and data block double-allocation.
- GCC or Clang on a POSIX-like environment
- Make (optional) for scripted builds
Compile the utilities using any standard C compiler:
gcc -o mkfs mkfs.c
gcc -o journal journal.c
gcc -o validator validator.cInitialize the vsfs.img file with the required structures:
./mkfsThis creates the superblock, reserves the root inode (Inode 0), and sets up the root directory.
Create a File
Stage a file creation in the journal:
./journal create <filename>This logs the necessary metadata updates to the journal region.
Commit Changes
Permanently apply the journaled updates to the disk:
./journal installThis applies all completed transactions and clears the journal.
Run the validator to identify any inconsistencies:
./validatorIf the filesystem is healthy, it reports: "Filesystem 'vsfs.img' is consistent."
| Parameter | Value |
|---|---|
| Block Size | 4096 Bytes |
| Inode Size | 128 Bytes |
| Max Direct Pointers | 8 |
| Max Files | 64 |
| Max Data Blocks | 64 |
| Superblock Magic | 0x56534653 |
| Journal Magic | 0x4A524E4C |
- Ahnaf Iqbal - Collaborator
- Md. Mahmudur Rahman - Collaborator
This project is provided for educational use in systems programming and operating systems courses.
Abdullah Al Fahad
