Refactor

src/fs.rs

@@ -1,3 +1,7 @@
+//! Simple wrapper around a FAT32 image exposed to the kernel.
+//!
+//! Implements a minimal disk backend and exposes a global FILE_SYSTEM used by
+//! the kernel to load user binaries.
 use core::{cell::UnsafeCell, ops::Deref};
 
 use bffs::{
@@ -7,10 +11,18 @@ use bffs::{
 
 const DISK_ADDR: *const u8 = 0x9000_0000 as *const _;
 
+/// Lazy holder for the kernel's filesystem instance.
+///
+/// The inner `UnsafeCell` allows one-time initialization at early boot while
+/// exposing a shared `&'static` reference through `Deref` once initialized.
 pub struct FSTemp(UnsafeCell<Option<Fat32FileSystem<Disk>>>);
 unsafe impl Sync for FSTemp {}
 
 impl FSTemp {
+    /// Initialize the global filesystem from the in-memory disk image.
+    ///
+    /// Safety: must be called exactly once during early kernel initialization
+    /// before any other filesystem operations occur.
     pub unsafe fn init(&self) {
         unsafe {
             *self.0.get() = Some(Fat32FileSystem::new(Disk::new(1024 * 1024 * 16)).unwrap());
@@ -29,12 +41,17 @@ impl Deref for FSTemp {
 pub static FILE_SYSTEM: FSTemp = FSTemp(UnsafeCell::new(None));
 
 #[derive(Debug)]
+/// Simple disk backend that reads from a fixed memory region.
+///
+/// The `Disk` struct provides `Read` and `Seek` implementations over a
+/// contiguous in-memory image exposed at DISK_ADDR.
 pub struct Disk {
     pos: u64,
     size: u64,
 }
 
 impl Disk {
+    /// Create a new `Disk` representing an in-memory image of `size` bytes.
     pub fn new(size: u64) -> Self {
         Self { pos: 0, size }
     }
@@ -56,12 +73,15 @@ impl Seek for Disk {
 }
 
 impl Read for Disk {
+    /// Read bytes from the in-memory disk image into `buf`.
     fn read(&mut self, buf: &mut [u8]) -> Result<usize, bffs::error::Error<Self::Error>> {
         if self.pos >= self.size {
             return Ok(0);
         }
         let size = usize::min(buf.len(), (self.size - self.pos) as usize);
-        (0..size).for_each(|i| buf[i] = unsafe { *DISK_ADDR.byte_add(i + self.pos as usize) });
+        for i in 0..size {
+            buf[i] = unsafe { *DISK_ADDR.byte_add(i + self.pos as usize) };
+        }
         self.pos += size as u64;
         Ok(size)
     }