power: proper shutdown via UEFI ResetSystem (ACPI S5)

- uefi.rs: full EFI_RUNTIME_SERVICES layout with reset_system at index 10
  (spec order); EfiResetSystem type + RESET_* constants
- power.rs: stash the runtime-services table pre-EBS; poweroff() calls
  ResetSystem(EfiResetShutdown) — still callable after ExitBootServices
  because we never call SetVirtualAddressMap, so the pointers keep
  working with physical addresses; falls back to the hlt loop
- shell: 'poweroff' and 'exit' shut the machine down (QEMU exits),
  'halt' keeps the plain hlt loop

1 files changed, 32 insertions, 2 deletions

diff --git a/rsnix/src/uefi.rs b/rsnix/src/uefi.rs
index 619739e..b1b5e48 100644
--- a/rsnix/src/uefi.rs
+++ b/rsnix/src/uefi.rs
@@ -86,12 +86,42 @@ pub struct SimpleTextInput {
 }
 
 // ---------------------------------------------------------------------------
-// Runtime services (stub — we don't use them)
+// Runtime services
 // ---------------------------------------------------------------------------
+
+/// `EFI_RESET_SYSTEM` — ResetType, ResetStatus, DataSize, ResetData.
+/// ResetType: 0 cold, 1 warm, 2 shutdown, 3 platform-specific.
+pub type EfiResetSystem =
+    unsafe extern "efiapi" fn(u32, u64, usize, *const u16) -> Status;
+
+pub const RESET_COLD: u32 = 0;
+#[allow(dead_code)]
+pub const RESET_WARM: u32 = 1;
+pub const RESET_SHUTDOWN: u32 = 2;
+#[allow(dead_code)]
+pub const RESET_PLATFORM_SPECIFIC: u32 = 3;
+
+/// EFI_RUNTIME_SERVICES — function pointers in spec order after the header.
+/// We only use ResetSystem; the rest stay opaque.  The table remains
+/// callable after ExitBootServices because we never call SetVirtualAddressMap,
+/// so the pointers keep working with physical (identity) addresses.
 #[repr(C)]
 pub struct RuntimeServices {
     _hdr: TableHeader,
-    _reserved: [*mut c_void; 30],
+    _get_time: *mut c_void,                  // 0
+    _set_time: *mut c_void,                  // 1
+    _get_wakeup_time: *mut c_void,           // 2
+    _set_wakeup_time: *mut c_void,           // 3
+    _set_virtual_address_map: *mut c_void,   // 4
+    _convert_pointer: *mut c_void,           // 5
+    _get_variable: *mut c_void,              // 6
+    _get_next_variable_name: *mut c_void,    // 7
+    _set_variable: *mut c_void,              // 8
+    _get_next_high_monotonic_count: *mut c_void, // 9
+    pub reset_system: EfiResetSystem,        // 10
+    _update_capsule: *mut c_void,            // 11
+    _query_capsule_capabilities: *mut c_void, // 12
+    _query_variable_info: *mut c_void,       // 13
 }
 
 // ---------------------------------------------------------------------------