Adapt everything in BT5 to new capnhook API

This includes:
- Renaming of functions (iohook_invoke_next)
- Slight interface changes (com_proxy_wrap, iohook_push_handler)
- De-duplicate stuff from utils (iobuf, hr)

src/main/unicorntail/dllmain.c

@@ -20,16 +20,13 @@
 static bool my_dll_entry_init(char *sidcode, struct property_node *param);
 static bool my_dll_entry_main(void);
 
-static const irp_handler_t unicorntail_handlers[] = {
-    p3io_filter_dispatch_irp,
-    usbmem_dispatch_irp,
-};
-
 static bool my_dll_entry_init(char *sidcode, struct property_node *param)
 {
     log_info("--- Begin unicorntail dll_entry_init ---");
 
-    iohook_init(unicorntail_handlers, lengthof(unicorntail_handlers));
+    iohook_push_handler(p3io_filter_dispatch_irp);
+    iohook_push_handler(usbmem_dispatch_irp);
+
     p3io_filter_init();
     usbmem_init();
 

src/main/unicorntail/p3io.c

@@ -55,7 +55,7 @@ p3io_filter_dispatch_irp(struct irp *irp)
     LeaveCriticalSection(&p3io_handle_lock);
 
     if (!match) {
-        return irp_invoke_next(irp);
+        return iohook_invoke_next(irp);
     }
 
     switch (irp->op) {
@@ -68,7 +68,7 @@ p3io_filter_dispatch_irp(struct irp *irp)
         case IRP_OP_READ:
             return p3io_handle_read(irp);
         default:
-            return irp_invoke_next(irp);
+            return iohook_invoke_next(irp);
     }
 }
 
@@ -93,7 +93,7 @@ static HRESULT p3io_handle_open(struct irp *irp)
 {
     HRESULT hr;
 
-    hr = irp_invoke_next(irp);
+    hr = iohook_invoke_next(irp);
 
     if (FAILED(hr)) {
         return hr;
@@ -169,7 +169,7 @@ static HRESULT p3io_handle_write(struct irp *irp)
             /* Non-UART command, break out here. */
             irp->write.pos = 0;
 
-            return irp_invoke_next(irp);
+            return iohook_invoke_next(irp);
     }
 
     /* Frame up and queue a response packet */
@@ -189,7 +189,7 @@ static HRESULT p3io_handle_read(struct irp *irp)
     if (p3io_resp.pos == 0) {
         LeaveCriticalSection(&p3io_cmd_lock);
 
-        return irp_invoke_next(irp);
+        return iohook_invoke_next(irp);
     } else {
         iobuf_flip(&tmp, &p3io_resp);
         iobuf_move(&irp->read, &tmp);

src/main/unicorntail/usbmem.c

@@ -35,7 +35,7 @@ void usbmem_fini(void)
         irp.op = IRP_OP_CLOSE;
         irp.fd = usbmem_fd;
 
-        irp_invoke_next(&irp);
+        iohook_invoke_next(&irp);
     }
 
     DeleteCriticalSection(&usbmem_lock);
@@ -54,7 +54,7 @@ usbmem_dispatch_irp(struct irp *irp)
     if (!usbmem_match_irp(irp)) {
         LeaveCriticalSection(&usbmem_lock);
 
-        return irp_invoke_next(irp);
+        return iohook_invoke_next(irp);
     } else {
         hr = usbmem_dispatch_irp_locked(irp);
         LeaveCriticalSection(&usbmem_lock);
@@ -94,7 +94,7 @@ static HRESULT usbmem_handle_open(struct irp *irp)
 {
     HRESULT hr;
 
-    hr = irp_invoke_next(irp);
+    hr = iohook_invoke_next(irp);
 
     if (SUCCEEDED(hr)) {
         log_info("Opened a real usbmem port");
@@ -108,7 +108,11 @@ static HRESULT usbmem_handle_open(struct irp *irp)
        start emulating a usbmem unit. */
 
     if (usbmem_fd == NULL || usbmem_fd == INVALID_HANDLE_VALUE) {
-        usbmem_fd = iohook_open_dummy_fd();
+        hr = iohook_open_nul_fd(&usbmem_fd);
+
+        if (hr != S_OK) {
+            log_fatal("Opening nul fd failed: %08lx", hr);
+        }
     }
 
     irp->fd = usbmem_fd;
@@ -120,7 +124,7 @@ static HRESULT usbmem_handle_close(struct irp *irp)
 {
     usbmem_fd = NULL;
 
-    return irp_invoke_next(irp);
+    return iohook_invoke_next(irp);
 }
 
 static HRESULT usbmem_handle_write(struct irp *irp)