ahci: SATA driver + FAT32 persistent disk mounted at /disk

- ahci.rs: polling AHCI on PCI class 1/6/1, bus mastering + ABAR map,
  port 0 up, IDENTIFY + READ/WRITE DMA EXT through one 4KiB DMA buffer
- fat.rs: BPB parse, whole-FAT RAM cache with write-back to both copies,
  LFN read/write, dirs, multi-cluster files, FSInfo free-count sync,
  space-padded dot entries ('..' = cluster 0 under root), fsck-clean
- fs.rs: /disk mount node + 24-slot ephemeral node pool; ls/cat/hexdump/
  echo/mkdir/touch/rm/edit all work on disk paths unchanged
- QEMU: explicit bus assignment (disk=ide.0, ESP=ide.1); the implicit
  fat:rw:esp drive was stealing AHCI port 0
- Debugged against QEMU source: header DW0 is CFL in bits 4:0 / PRDTL in
  bits 31:16 (Linux libahci layout), FIS count at bytes 12-13, device at
  byte 7; QEMU rejects H2D FIS flags bits 6:4, so direction is the
  header W bit only
- Verified: full shell round-trip on /disk, reboot persistence (poweroff
  then mdir/mtype and a fresh boot), fsck.fat clean

1 files changed, 10 insertions, 0 deletions

diff --git a/rsdos/src/main.rs b/rsdos/src/main.rs
index c36660e..181d3e2 100644
--- a/rsdos/src/main.rs
+++ b/rsdos/src/main.rs
@@ -166,6 +166,16 @@ pub extern "efiapi" fn efi_main(image_handle: Handle, system_table: *mut SystemT
     let devices = rsnix::pci::probe();
     rsnix::serial_println!("pci: {} device(s) on all buses", devices.len());
 
+    // Disk: AHCI SATA driver, then mount a FAT32 volume if one is attached.
+    if !rsnix::ahci::init() {
+        rsnix::serial_println!("ahci: no disk attached");
+    }
+    if rsnix::fat::init() {
+        rsnix::serial_println!("fat: volume mounted at /disk");
+    } else {
+        rsnix::serial_println!("fat: no FAT32 volume");
+    }
+
     let (dirs, files) = rsnix::fs::init();
     rsnix::serial_println!("fs: vfs ready — {} dirs, {} files", dirs, files);
     if rsnix::fs::self_test() {