Add basic filesystem ideas writeup

src/SUMMARY.md

@@ -8,7 +8,7 @@
         - [Security Features]()
         - [Microkernel]()
         - [GUI]()
-        - [Filesystem]()
+        - [Filesystem](development/design/filesystem.md)
     - [Configuring a Build Environment](development/environment.md)
     - [Development Workflow](development/workflow.md)
 - [Using the OS](user/README.md)

src/development/design/filesystem.md

@@ -1 +1,75 @@
 # Filesystem
+```admonish warning
+I have *no* idea what I'm doing here. If you do, *please* let me know, and fix this!
+This is just some light brainstorming of how I think this might work.
+```
+
+## Prelude
+Right now, [actors](/development/design/actor.md) are stored in **RAM** only.
+But, what if we want them to be persistent on system reboot? They need to be saved to the disk.
+
+I don't want to provide a simple filesystem interface to programs like **UNIX** does however.
+Instead, all data should be just stored in *actors*, then the actors will decide whether or not they should be saved.
+They can save at any time, save immediately, or just save on a *shutdown* signal.
+
+Therefore, the "filesystem" code will just be a library that's simple a low-level interface for actors to use.
+
+
+## Filesystem Layout
+### Partition
+A virtual section of the disk.
+- **BOOT Partition:** Fixed-size partition at the beginning of the disk, containing the kernel code, and info about the other partitions.
+- **DATA Partition:** Fixed-size partition containing misc. *Actor* data
+- **USER Partition:** Contains all data from the `User` [namespace](/development/design/actor.md#namespaces)
+```rust
+enum PartitionLabel {
+    Boot,
+    Data,
+    User,
+}
+
+struct PartitionHeader {
+    label: PartitionLabel,
+    num_chunks: u64, // Chunks in this partition
+}
+```
+
+### Chunk
+Small pieces that each partition is split into.
+Contains fixed-length metadata (checksum, dates) at the beginning, and then arbitrary data afterwards.
+If the saved data exceeds past a single chunk, the metadata lists this.
+```rust
+struct Chunk {
+    checksum: u64,
+    extends: bool,
+    data: [u8; 512],
+}
+```
+This struct is then encoded into bytes and written to the disk. Drivers for the disk are *to be implemented*.
+It *should* be possible to do autodetection, and maybe for *Actors* to specify which disk/partition they want to be saved to.
+
+### Reading
+On boot, we start executing code from the beginning of the disk (the boot partition, although that's meaningless at this point).
+The `kernel` then reads in bytes from the first partition *(as the **BOOT** partition is fixed-size, we know when this starts)* into memory, serializing it into a `PartitionHeader` struct via [bincode](https://lib.rs/crates/bincode).
+
+From here, as we have a fixed `CHUNK_SIZE`, and know how many chunks are in our first partition, we can read from any chunk on any partition now.
+On startup, an *Actor* can request to read data from the disk. If it has the right [capabilities](/development/design/actor.md#ocap), we find the chunk it's looking for[^find_chunk], parse the data (using `bincode` again), and send it back.
+
+Also, we are able to verify data. Before passing off the data, we re-hash it using [ahash](https://lib.rs/crates/ahash) to see if it matches.
+If it does, we simply pass it along like normal. If not, we refuse, and send an error [message](/development/design/actor.md#messages).
+
+### Writing
+Writing uses a similar process. An *Actor* can request to write data. If it has proper capabilties, we serialize the data, allocate a free chunk[^free_chunk], and write to it.
+We *hash* the data first to generate a checksum, and set proper metadata if the data extends past the `CHUNK_SIZE`.
+
+### Permissions
+Again, whether actors can:
+- Write to a specific disk/partition
+- Write to disk at all
+- Read from disk
+
+will be determined via [capabilities](/development/design/actor.md#ocap)
+
+[^find_chunk]: Currently via magic. I have no idea how to do this other than a simple search. Maybe generate an index, or use a **UUID**?
+
+[^free_chunk]: Again, no idea how.