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https://github.com/novara754/tfs
TFS is a small and simple filesystem designed by me for self-educational purposes.
https://github.com/novara754/tfs
Last synced: 24 days ago
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TFS is a small and simple filesystem designed by me for self-educational purposes.
- Host: GitHub
- URL: https://github.com/novara754/tfs
- Owner: novara754
- License: mit
- Created: 2021-02-28T13:19:29.000Z (over 3 years ago)
- Default Branch: main
- Last Pushed: 2021-02-28T13:28:44.000Z (over 3 years ago)
- Last Synced: 2024-01-14T23:13:17.239Z (10 months ago)
- Language: C++
- Size: 33.2 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# TFS - Tiny File System
TFS is a small and simple filesystem designed by me for self-educational
purposes. This project implements the filesystem in userspace
using [libfuse](https://github.com/libfuse/libfuse).
## Building & running
**Requirements:**
- [Python3](https://www.python.org/download/releases/3.0/)
- [GNU Make](https://www.gnu.org/software/make/)
- [g++](https://gcc.gnu.org/) with C++ 2a support
- [libfuse3](https://github.com/libfuse/libfuse)
Compile the filesystem driver simply using `make all`, then
it can be executed using `./tfs [options]`.
- `` is a binary file containing a TFS formatted filesystem, you
can generate one using the `make-img.py` script in the `scripts` folder.
- `` is where you want to mount the new filesystem.
- `[options]` is an optional list of FUSE options.
To quickly get started run the following commands:
```
$ make all
$ ./scripts/make-img.py
$ ./tfs ./test/test.img /tmp/tfs-mount
```
A sample filesystem will be mounted at `/tmp/tfs-mount`.
## Filesystem Design
### Overview
```
+-------------------------+
| |
| Bootsector |
| |
+-------------------------+
| |
| Reserved blocks (0..n) |
| |
+-------------------------+
| |
| Block usage bitmap |
| |
+-------------------------+
| |
| Root directory |
| |
+-------------------------+
| |
| Data blocks (0..16384) |
| |
+-------------------------+
```
The filesystem is split into 1024-byte blocks.
### Reserved blocks
At the very beginning there are blocks reserved for the bootloader.
There is always at least one of these blocks, however more can be added as
needed. The number of additional reserved blocks can be set by changing the 510th byte in the first block, directly in front of the
[BIOS Boot Signature](https://en.wikipedia.org/wiki/Master_boot_record#SIG).
A value of `0x00` sets just one reserved block, `0x01` for two, and so on.
### Block usage bitmap
After the [reserved blocks](#reserved-blocks) follows a "Block Usage Bitmap"
which spans 2 blocks. Each bit in these two blocks corresponds to one of the
[data blocks](#data-blocks) and signifies whether the data block is in use (1)
or not (0).
Because the bitmap is 16384 bits long (`2 * 1024 * 8`) and as such 16384 blocks
can be mapped, roughly 16 MiB of storage are available.
### Directories
Directories are single blocks made up of sequence of
[directory-entries](#directory-entries).
As each directory entry is 16 bytes long and a directory is 1024 bytes long,
there is a maximum 64 entries per directory.
Each entry in a directory can either be a file or another directory.
Every directory's first two entries are a loopback entry (name ".") pointing
to the directory itself and a parent entry (name "..") pointing to its parent.
The root directory has no parent entry because it has no parent.
### Files
Files are consecutive blocks containing nothing but their raw data.
Files are identified by directory entries pointing to their respective
blocks.
### Root directory
The root directory is a [directory](#directories) right after the
[block usage bitmap](#block-usage-bitmap) and represents the root of the
filesystem tree.
It is not part of the block usage bitmap because it always exists and always
takes up a single block.
### Directory entries
Directory entries are 16-byte structures laid out as follows:
| Field | Offset (bytes) | Length (bytes) |
|-------------|---------------:|---------------:|
| Name | 0 | 10 |
| Start block | 10 | 2 |
| Num blocks | 12 | 2 |
| Size | 14 | 2 |
**Name:**
The name of the file or directory stored in 7-bit ASCII encoding.
Allowed is everything from `0x20` to `0x7D` except for `0x2F` (`"/"`).
The MSB of the first byte signifies whether the entry is for a file (0)
or another directory (1).
Unused bytes in the filename are to be set to `0x00`.
**Start block:**
Index of the first data block of the file or directory. Keep in mind that
data blocks start *after* the root directory. An index of 0 corresponds to the
first block after the root directory.
**Num blocks:**
The number of blocks the file occupies. Ignored when file is a directory.
**Size:**
The number of bytes occupying the last block of the file (all other blocks
are always full).
An unused entry has all its bytes set to `0x7F`, while an entry consisting of
only `0x00` marks the end of a directory, no more used entries may follow it.
## License
Licensed under the [MIT License](./LICENSE).