[PATCH QEMU HCI-8.0 v5 06/13] usb-host: drain before the host controller is migrated #VSTOR-137800

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

.pre_save() drains the device's URBs, but at the default section
priority the xHCI controller is saved before any usb-host device -> its
state is already on the wire when the drain runs.

All usb-host devices share one libusb context, so draining one reaps
another's completed transfers too.  Each completion pokes xHCI (writes
an event, queues the next TD) after xHCI has been saved, and the target
then resumes from a stale controller: OUT data sent twice, IN data lost.

Raise usb-host above MIG_PRI_DEFAULT so every device drains before its
host controller is saved.  Sections are matched by name, so the
reordered stream stays compatible.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 hw/usb/host-libusb.c        | 1 +
 include/migration/vmstate.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index ebad04ec305..9e9ee7d305f 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -1922,6 +1922,7 @@ static const VMStateDescription vmstate_usb_host = {
     .name = "usb-host",
     .version_id = 1,
     .minimum_version_id = 1,
+    .priority = MIG_PRI_USB_HOST,
     .pre_save = usb_host_pre_save,
     .post_load = usb_host_post_load,
     .fields = (const VMStateField[]) {
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 6839117be87..3358d7fedc8 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -160,6 +160,7 @@ typedef enum {
 
     MIG_PRI_LOW,                /* Must happen after default */
     MIG_PRI_DEFAULT,
+    MIG_PRI_USB_HOST,           /* Must be saved before the host controller */
     MIG_PRI_IOMMU,              /* Must happen before PCI devices */
     MIG_PRI_PCI_BUS,            /* Must happen before IOMMU */
     MIG_PRI_VIRTIO_MEM,         /* Must happen before IOMMU */

-- 
2.47.1