Preparation for improved u2f-passthru hidraw handle lifetimes:

These callbacks can be implemented by the backing implementation,
i.e. u2f-passthru or u2f-emulated.

The start callback is invoked when the device receives an INTR IN, and
the stop callback is invoked when the endpoint has been unlinked/stopped.

For a Linux guest, the start callback corresponds to the `hid_hw_open` and
`hid_hw_close` routines, invoked whenever the first user opens, respectively
the last user closes the emulated hidraw device.

Signed-off-by: David Bouman <dbouman03@gmail.com>
---
 hw/usb/u2f.c | 23 +++++++++++++++++++++++
 hw/usb/u2f.h |  5 +++++
 2 files changed, 28 insertions(+)

diff --git a/hw/usb/u2f.c b/hw/usb/u2f.c
index 1fb59cf404..cc1abd6c7d 100644
--- a/hw/usb/u2f.c
+++ b/hw/usb/u2f.c
@@ -253,6 +253,12 @@ static void u2f_key_handle_data(USBDevice *dev, USBPacket *p)
     case USB_TOKEN_IN:
         packet_in = u2f_pending_in_get(key);
         if (packet_in == NULL) {
+            U2FKeyClass *kc = U2F_KEY_GET_CLASS(key);
+
+            /* An early INTR IN is sent to kick the device. */
+            if (!key->started) {
+                key->started = (kc->start ? kc->start(key) : true);
+            }
             p->status = USB_RET_NAK;
             return;
         }
@@ -317,6 +323,21 @@ const VMStateDescription vmstate_u2f_key = {
     }
 };
 
+static void u2f_ep_stopped(USBDevice *dev, USBEndpoint *ep)
+{
+    U2FKeyState *key = U2F_KEY(dev);
+    U2FKeyClass *kc = U2F_KEY_GET_CLASS(key);
+
+    if (!key->started) {
+        return;
+    }
+    if (kc->stop) {
+        kc->stop(key);
+    }
+    key->started = false;
+}
+
+
 static void u2f_key_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -332,6 +353,8 @@ static void u2f_key_class_init(ObjectClass *klass, void *data)
     uc->unrealize      = u2f_key_unrealize;
     dc->desc           = "QEMU U2F key";
     dc->vmsd           = &vmstate_u2f_key;
+
+    uc->ep_stopped     = u2f_ep_stopped;
 }
 
 static const TypeInfo u2f_key_info = {
diff --git a/hw/usb/u2f.h b/hw/usb/u2f.h
index 8bff13141a..56d989c783 100644
--- a/hw/usb/u2f.h
+++ b/hw/usb/u2f.h
@@ -49,6 +49,9 @@ struct U2FKeyClass {
                             const uint8_t packet[U2FHID_PACKET_SIZE]);
     void (*realize)(U2FKeyState *key, Error **errp);
     void (*unrealize)(U2FKeyState *key);
+
+    bool (*start)(U2FKeyState *key);
+    void (*stop)(U2FKeyState *key);
 };
 
 /*
@@ -64,6 +67,8 @@ struct U2FKeyState {
     uint8_t pending_in_start;
     uint8_t pending_in_end;
     uint8_t pending_in_num;
+
+    bool started;
 };
 
 /*
-- 
2.34.1