[QEMU HCI-8.0 PATCH v2 10/13] usb: migrate the interface altsetting #VSTOR-137800

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

The active altsetting of each interface is host controller state that
the guest selected with SET_INTERFACE, but it isn't part of the
migration stream.  For most devices the target happens to reopen on the
same altsettings, so this went unnoticed.

It matters for CPR of a device whose endpoints only exist on a non-zero
altsetting, such as an isochronous streaming interface.  Migrate the
altsetting array in a subsection, gated to the CPR modes: only the CPR
target consumes it to rebuild its endpoints, while a regular migration
reopens the device and reconstructs the altsetting itself.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 hw/usb/bus.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/hw/usb/bus.c b/hw/usb/bus.c
index 8dd2ce415eb..ee13acea658 100644
--- a/hw/usb/bus.c
+++ b/hw/usb/bus.c
@@ -8,6 +8,7 @@
 #include "qemu/module.h"
 #include "system/system.h"
 #include "migration/vmstate.h"
+#include "migration/cpr.h"
 #include "monitor/monitor.h"
 #include "trace.h"
 #include "qemu/cutils.h"
@@ -63,6 +64,37 @@ static int usb_device_post_load(void *opaque, int version_id)
     return 0;
 }
 
+static bool usb_altsetting_needed(void *opaque)
+{
+    USBDevice *dev = opaque;
+    int i;
+
+    /*
+     * Only the CPR target consumes this, to rebuild its endpoints; other
+     * migrations reopen the device and reconstruct the altsetting.
+     */
+    if (!cpr_incoming_needed(NULL)) {
+        return false;
+    }
+    for (i = 0; i < USB_MAX_INTERFACES; i++) {
+        if (dev->altsetting[i]) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static const VMStateDescription vmstate_usb_device_altsetting = {
+    .name = "USBDevice/altsetting",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = usb_altsetting_needed,
+    .fields = (const VMStateField[]) {
+        VMSTATE_INT32_ARRAY(altsetting, USBDevice, USB_MAX_INTERFACES),
+        VMSTATE_END_OF_LIST(),
+    }
+};
+
 const VMStateDescription vmstate_usb_device = {
     .name = "USBDevice",
     .version_id = 1,
@@ -77,6 +109,10 @@ const VMStateDescription vmstate_usb_device = {
         VMSTATE_INT32(setup_index, USBDevice),
         VMSTATE_UINT8_ARRAY(setup_buf, USBDevice, 8),
         VMSTATE_END_OF_LIST(),
+    },
+    .subsections = (const VMStateDescription * const []) {
+        &vmstate_usb_device_altsetting,
+        NULL
     }
 };
 
-- 
2.47.1