[RealityVoid]

Soooo... how does it work?

I'm not asking about the structure or how it's organized. I mean... is the filesystem in a file or... how?

Background: I mostly do embedded stuff so at a glance I would have expected low level primitives (like, HW interactions, registers and stuff) but I see none. So maybe, my expectation, when tacking a problem, of interacting with the HW directly, does not stand in modern environments.

Even better, but unrelated question... how the heck does a x86 OS request data from the HDD?

[mcpherrinm]

You'd presumably have some "block device" abstraction between your filesystem and your device driver. Don't want to re-implement a FS for each type of hardware. On a Linux system, you can read, eg, /dev/sda1 from userspace, which is what it looks like this filesystem probably does.

As for how you actually request data from the hard drive: There's older ATA interfaces, and BIOS routines from them, which I suspect is what most hobbyist OSes would use.

A more modern interface is AHCI. The OSDev wiki has an overview, where you can see how the registers work: https://wiki.osdev.org/AHCI

[keithnz]

as an aside, for our embedded system we use https://github.com/ARMmbed/littlefs for our flash file system, it has a bit of a description on its design and its copy on write system so that it can handle random power loss. Be nice to see some of these kinds of libraries done in Nim or Rust.

[brandmeyer]

> how the heck does a x86 OS request data from the HDD?

Entirely too short summary: Use PCI to discover the various devices attached to the CPU. One or more of them are AHCI or NVMe devices. The AHCI and NVMe standards each describe sets of memory-mapped configuration registers and DMA engines. Eventually, you get to a point where you can describe linked lists of transactions to be executed that are semantically similar to preadv, pwritev, and so on.

There's tons of info on osdev.org, such as https://wiki.osdev.org/AHCI

[rrdharan]

https://en.m.wikipedia.org/wiki/INT_13H

[pkaye]

Looks like a filesystem in a file.