usb-host: live migration support

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/host-linux.c

@@ -111,6 +111,7 @@ typedef struct USBHostDevice {
     uint32_t  iso_urb_count;
     uint32_t  options;
     Notifier  exit;
+    QEMUBH    *bh;
 
     struct endp_data ep_in[USB_MAX_ENDPOINTS];
     struct endp_data ep_out[USB_MAX_ENDPOINTS];
@@ -1421,6 +1422,43 @@ static void usb_host_exit_notifier(struct Notifier *n, void *data)
     }
 }
 
+/*
+ * This is *NOT* about restoring state.  We have absolutely no idea
+ * what state the host device is in at the moment and whenever it is
+ * still present in the first place.  Attemping to contine where we
+ * left off is impossible.
+ *
+ * What we are going to to to here is emulate a surprise removal of
+ * the usb device passed through, then kick host scan so the device
+ * will get re-attached (and re-initialized by the guest) in case it
+ * is still present.
+ *
+ * As the device removal will change the state of other devices (usb
+ * host controller, most likely interrupt controller too) we have to
+ * wait with it until *all* vmstate is loaded.  Thus post_load just
+ * kicks a bottom half which then does the actual work.
+ */
+static void usb_host_post_load_bh(void *opaque)
+{
+    USBHostDevice *dev = opaque;
+
+    if (dev->fd != -1) {
+        usb_host_close(dev);
+    }
+    if (dev->dev.attached) {
+        usb_device_detach(&dev->dev);
+    }
+    usb_host_auto_check(NULL);
+}
+
+static int usb_host_post_load(void *opaque, int version_id)
+{
+    USBHostDevice *dev = opaque;
+
+    qemu_bh_schedule(dev->bh);
+    return 0;
+}
+
 static int usb_host_initfn(USBDevice *dev)
 {
     USBHostDevice *s = DO_UPCAST(USBHostDevice, dev, dev);
@@ -1432,6 +1470,7 @@ static int usb_host_initfn(USBDevice *dev)
     QTAILQ_INSERT_TAIL(&hostdevs, s, next);
     s->exit.notify = usb_host_exit_notifier;
     qemu_add_exit_notifier(&s->exit);
+    s->bh = qemu_bh_new(usb_host_post_load_bh, s);
     usb_host_auto_check(NULL);
 
     if (s->match.bus_num != 0 && s->match.port != NULL) {
@@ -1443,7 +1482,13 @@ static int usb_host_initfn(USBDevice *dev)
 
 static const VMStateDescription vmstate_usb_host = {
     .name = "usb-host",
-    .unmigratable = 1,
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = usb_host_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_USB_DEVICE(dev, USBHostDevice),
+        VMSTATE_END_OF_LIST()
+    }
 };
 
 static Property usb_host_dev_properties[] = {