v0.5.5: crash reports go to a dedicated CRASHLOG USB stick

The fault handler now writes crash.log to the volume labeled CRASHLOG
(label-selected via fat::crash_vol), falling back to slot 0.  On real
hardware the boot USB may be unwritable, so a second stick labeled
CRASHLOG survives the write; the shell auto-prints the previous crash
report from it at next boot (read_crash_log resolves /disk/<uid>/crash.log
through the FAT path, since Disk nodes hold no cached children).

- fat.rs: volume_label() + crash_vol() (no allocation)
- fs.rs: write_crash_log targets crash_vol(); read_crash_log prefers the
  CRASHLOG disk node; drop now-unused first_disk()
- mkdisk.sh: --label option
- test-fault.sh: boots with a dedicated CRASHLOG stick (mkfs -F 32 -n
  CRASHLOG), verifies crash.log lands there and NOT on the ESP

1 files changed, 26 insertions, 0 deletions

diff --git a/rsnix/src/uefi.rs b/rsnix/src/uefi.rs
index c311ad9..234ad65 100644
--- a/rsnix/src/uefi.rs
+++ b/rsnix/src/uefi.rs
@@ -40,6 +40,32 @@ pub const EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID: Guid = Guid {
     d: [0x96, 0xfb, 0x7a, 0xde, 0xd0, 0x80, 0x51, 0x6a],
 };
 
+pub const EFI_LOADED_IMAGE_PROTOCOL_GUID: Guid = Guid {
+    a: 0x5b1b31a1,
+    b: 0x9562,
+    c: 0x11d2,
+    d: [0x8e, 0x3f, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b],
+};
+
+/// Minimal EFI_LOADED_IMAGE_PROTOCOL — we only need the image base/size
+/// to reserve the kernel's own code/data/bss pages so the heap and page
+/// allocators can never overwrite the running kernel.
+#[repr(C)]
+pub struct LoadedImageProtocol {
+    pub revision: u32,
+    _pad0: u32,
+    pub parent_handle: Handle,
+    pub system_table: *mut core::ffi::c_void,
+    pub device_handle: Handle,
+    pub file_path: *mut core::ffi::c_void,
+    _reserved: *mut core::ffi::c_void,
+    pub load_options_size: u32,
+    _pad1: u32,
+    pub load_options: *mut core::ffi::c_void,
+    pub image_base: *mut core::ffi::c_void,
+    pub image_size: u64,
+}
+
 // ---------------------------------------------------------------------------
 // Table header
 // ---------------------------------------------------------------------------