This is partial revert of commit e058fa2dd599.

The portion to immediately validate the device is kept, but this
adds and enables again the autoscan functionality. This is needed
to detect and relay USB device disconnect event to the guest.

Fixes: e058fa2dd599 ("usb-host: add special case for bus+addr")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3111
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
---
 hw/usb/host-libusb.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index b74670ae25696b5252f0d034cb9b759e338a050f..f0baf6b2f2d12fbf8feb5b788b46d3187028df58 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -90,7 +90,6 @@ struct USBHostDevice {
     uint32_t                         iso_urb_frames;
     uint32_t                         options;
     uint32_t                         loglevel;
-    bool                             needs_autoscan;
     bool                             allow_one_guest_reset;
     bool                             allow_all_guest_resets;
     bool                             suppress_remote_wake;
@@ -1211,7 +1210,6 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
 #if LIBUSB_API_VERSION >= 0x01000107 && !defined(CONFIG_WIN32)
     if (s->hostdevice) {
         int fd;
-        s->needs_autoscan = false;
         fd = qemu_open(s->hostdevice, O_RDWR, errp);
         if (fd < 0) {
             return;
@@ -1227,7 +1225,6 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
         !s->match.vendor_id &&
         !s->match.product_id &&
         !s->match.port) {
-        s->needs_autoscan = false;
         ldev = usb_host_find_ref(s->match.bus_num,
                                  s->match.addr);
         if (!ldev) {
@@ -1242,14 +1239,13 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
                        s->match.bus_num, s->match.addr);
             return;
         }
-    } else {
-        s->needs_autoscan = true;
-        QTAILQ_INSERT_TAIL(&hostdevs, s, next);
-        usb_host_auto_check(NULL);
     }
 
     s->exit.notify = usb_host_exit_notifier;
     qemu_add_exit_notifier(&s->exit);
+
+    QTAILQ_INSERT_TAIL(&hostdevs, s, next);
+    usb_host_auto_check(NULL);
 }
 
 static void usb_host_instance_init(Object *obj)
@@ -1267,9 +1263,7 @@ static void usb_host_unrealize(USBDevice *udev)
     USBHostDevice *s = USB_HOST_DEVICE(udev);
 
     qemu_remove_exit_notifier(&s->exit);
-    if (s->needs_autoscan) {
-        QTAILQ_REMOVE(&hostdevs, s, next);
-    }
+    QTAILQ_REMOVE(&hostdevs, s, next);
     usb_host_close(s);
 }
 

---
base-commit: 190d5d7fd725ff754f94e8e0cbfb69f279c82b5d
change-id: 20250912-usbhost-disconnect-192ecaa8fc3e

Best regards,
-- 
Timo Teräs <timo.teras@iki.fi>