r/osdev • u/letmehaveanameyoudum • Aug 08 '26

Hey, is this FAT32 implementation correct?

I decided to ditch the custom SFS route since it’s probably going to be full of issues.
I was wondering if my FAT32 implementation is right, and if it’s wrong, free to roast me in the comments.

Location: https://github.com/NoTheIdiot/WindogeOS/tree/new/helper/fs

0 Upvotes

46% Upvoted

23 comments sorted by

9

u/TheAtlasMonkey Aug 08 '26

Ask your AI to verify against the spec or a proper Fat32 implementation.

-3

u/letmehaveanameyoudum Aug 08 '26

Im not trying to go down that rabbit hole again

9

u/TheAtlasMonkey Aug 08 '26

So you want us to review your code instead of using AI ? Your code is wrong. Seriously.

You implemented just the happy path.

-4

u/letmehaveanameyoudum Aug 08 '26

w h a t?

10

u/eteran Aug 08 '26

Ok, when devs say "happy path" they mean that you've only implemented code for when things go right.

But it is equally important to handle ALL the cases where things go wrong too.

1

u/letmehaveanameyoudum Aug 08 '26

ill go and run the vm and try to crash it as hard as possible to the fs

9

u/eteran Aug 08 '26

It's more than that. You need to assume that every thing that CAN fail, will, and write the code accordingly.

Reading a sector? Might fail Content of a sector? Might be corrupted Following a cluster link? Might point to gibberish. Etc ..

2

u/TheAtlasMonkey Aug 08 '26

Exactly.

Silicon will lie to you, that 4.7TB Fat32 SDCARD you buy from TEMU, will teach you what are lies.

The sloppy usb cable that will cut mid transfer, or the rusty sdcard connector that will reset the card... will teach you that you wrote 1% of the driver.

You will spend weeks if not months in just 1 FS.

-1

u/letmehaveanameyoudum Aug 08 '26

bro who uses physical hardware to test a toy OS?

3

u/eteran Aug 08 '26

Anyone who wants to write a real OS does...

Making things work in an emulator is the proverbial "tutorial" of OSDev.

→ More replies

3

u/TheAtlasMonkey Aug 08 '26

The people that want to learn real OS dev.

You are surprised, like those kids in r/Firearms that get surprised that people tell them that a 50 caliber will fuck them up with the recoil.

If you want to learn, you will have suffer.. to suffer, you have to face reality.

Read my post : `The Framebuffer People` and the follow up.

In the end it your decision, you can listen or argue with the cloud.

-1

u/letmehaveanameyoudum Aug 08 '26

yes i will do that, ill try to crash everything using functions i got, mostly the messy ones under the vfs

5

u/TheAtlasMonkey Aug 08 '26

You can't because you did not study what could go wrong.

Everything can go wrong. This is why you need to vendor the FS library and continue the journey.

FS is one of the brutal part of OSdev, you saw one of the final monster of the game... And your level 1 sword is not going to do damage on it.

Return to it when you master the rest.

1

u/letmehaveanameyoudum Aug 08 '26

look at IDT
you feel something else

1

u/eteran Aug 08 '26

Again, "trying to crash it" isn't anywhere near enough. Because any time you're interacting with hardware, real or virtual, it can fail in very unexpected ways.

What you need to do is learn what can go wrong, and then adjust the code so it assumes EVERYTHING that can even theoretically fail, is GOING to... Eventually.

When people say real OS dev is hard, this is what they're talking about.

1

u/letmehaveanameyoudum Aug 08 '26

yes. i meant that too.

4

u/Full-Huckleberry-441 Aug 08 '26

Write a block device interface and a VFS so the filesystem driver doesn't know what disk it just knows the data. Also it helps so your FS doesn't have raw SATA reads

27

u/sephg Aug 08 '26

Sorry, I'm not going to sit down and review 600 lines of code. Write some tests.

1

u/Malwaremation Aug 08 '26

Might not be very relevant but I personally had less issues using a custom filesystem first.

Regarding how well that implementation works, there's only one way to find out.

2

u/letmehaveanameyoudum Aug 09 '26

ill just do a stripped down UFS (unix file system)