implement proper IRQL, DPCs, kernel and user APCs, alertable waits, async file I/O with cancellation, trap frames, selftests, a real driver/device model, native async FAT32, VFAT dotfile fixes, syscall ABI cleanup, async_apc and async_cancel tests, POSIX multi-volume paths, and pimp the readme.

code/hal/hal_keyboard.c

@@ -17,6 +17,17 @@ static uint8_t      gBuf[KBD_BUF_SIZE];
 static volatile int gHead = 0;
 static volatile int gTail = 0;
 
+// -- Deferred callback queue ---------------------------------------------------
+// The hard IRQ path updates the key state and stores completed make codes.
+// Optional client callbacks are delivered later from the kernel-queued DPC,
+// never directly from DIRQL/ISR context.
+#define KBD_DPC_BUF_SIZE  128u
+#define KBD_DPC_BUF_MASK  (KBD_DPC_BUF_SIZE - 1u)
+
+static uint8_t      gDpcBuf[KBD_DPC_BUF_SIZE];
+static volatile int gDpcHead = 0;
+static volatile int gDpcTail = 0;
+
 // -- Live Key State (for GetAsyncKeyState) ------------------------------------
 // These arrays track whether a key is currently held down.
 static volatile uint8_t gKeyState[128];    // Standard scan codes
@@ -62,6 +73,21 @@ static const char gShifted[128] = {
     0, 0, 0, 0, 0, '7','8','9','-', '4','5','6','+', '1','2','3','0','.'
 };
 
+// -- Deferred callback delivery ------------------------------------------------
+static void KbdDpc(void) {
+    for (;;) {
+        if (gDpcHead == gDpcTail)
+            break;
+
+        uint8_t make = gDpcBuf[gDpcHead];
+        gDpcHead = (gDpcHead + 1) & (int)KBD_DPC_BUF_MASK;
+
+        void (*cb)(uint8_t) = (void (*)(uint8_t))gCallback;
+        if (cb)
+            cb(make);
+    }
+}
+
 // -- ISR: The Engine -----------------------------------------------------------
 void KbdIsr(void) {
     uint8_t sc = __inbyte(PS2_DATA);
@@ -108,8 +134,15 @@ void KbdIsr(void) {
             gTail = next;
         }
         
-        void (*cb)(uint8_t) = (void (*)(uint8_t))gCallback;
-        if (cb) cb(make);
+        // Queue optional callback delivery to the DPC path.  Keep a separate
+        // callback queue so the public ReadScancode ring remains independent.
+        if (gCallback) {
+            int dpcNext = (gDpcTail + 1) & (int)KBD_DPC_BUF_MASK;
+            if (dpcNext != gDpcHead) {
+                gDpcBuf[gDpcTail] = make;
+                gDpcTail = dpcNext;
+            }
+        }
     }
 }
 
@@ -146,6 +179,14 @@ static char KbdReadChar(void) {
     return shifted ? gShifted[make] : gUnshifted[make];
 }
 
+static uint32_t KbdGetModifiers(void) {
+    return gModifiers;
+}
+
+static void KbdSetCallback(void (*cb)(uint8_t scancode)) {
+    gCallback = cb;
+}
+
 void HalKeyboardInitialize(HAL_KEYBOARD *out) {
     while (__inbyte(PS2_STAT) & 2); 
     __outbyte(PS2_CMD, 0xA8); 
@@ -154,7 +195,10 @@ void HalKeyboardInitialize(HAL_KEYBOARD *out) {
     out->Poll         = KbdPoll;
     out->ReadScancode = KbdReadScancode;
     out->ReadChar     = KbdReadChar;
+    out->GetModifiers = KbdGetModifiers;
+    out->SetCallback  = KbdSetCallback;
     out->IsKeyDown    = KbdIsKeyDown;
     out->Isr          = KbdIsr;
+    out->Dpc          = KbdDpc;
     out->IrqNumber    = 1;
 }