Re: [Qemu-devel] VMState assertion for USB devices on multiple buses

[Gerd Hoffmann <kraxel@redhat.com>]

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On 08/18/11 20:04, Daniel P. Berrange wrote:
> I've been experimenting with multiple USB2 buses, and device physical port
> addressing. It seems if you have 2 devices of the same type on the same
> port, but in different buses, you get a bogus VMState assertion failure

>      qemu-system-x86_64: savevm.c:1260: vmstate_register_with_alias_id: Assertion `!se->compat || se->instance_id == 0' failed.
>      Aborted

> AFAICT, the problem is that the 'se->idstr' field in the SaveStateEntry
> struct is not getting a unique enough value.
>
> Both the USB devices get idstr named   "1/usb-ccid", which IIUC is a
> combination of the device type and the port number.

Indeed.

> IMHO, it needs to have the USB bus name in there too eg. in this
> example it should have been
>
>      ehci0.0/1/usb-ccid
>      ehci1.0/1/usb-ccid

I assumed the savevm code walks up the device path and creates a unique 
name by prefixing the string with the parents pci address, but it 
doesn't :-(

We can do that outself though, see attached patch.
That gives us IDs like this:

   0000:00:01.2/uhci              (hcd, unchanged)
   0000:00:01.2/1/usb-ptr         (usb devs, now with hcd pci addr)

Juan?  Does that look sane?

cheers,
   Gerd

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diff --git a/hw/usb-bus.c b/hw/usb-bus.c
index c0bbc7c..477d57f 100644
--- a/hw/usb-bus.c
+++ b/hw/usb-bus.c
@@ -342,7 +342,20 @@ static void usb_bus_dev_print(Monitor *mon, DeviceState *qdev, int indent)
 static char *usb_get_dev_path(DeviceState *qdev)
 {
     USBDevice *dev = DO_UPCAST(USBDevice, qdev, qdev);
-    return g_strdup(dev->port->path);
+    DeviceState *hcd = qdev->parent_bus->parent;
+    char *id = NULL;
+
+    if (hcd && hcd->parent_bus && hcd->parent_bus->info->get_dev_path) {
+        id = hcd->parent_bus->info->get_dev_path(hcd);
+    }
+    if (id) {
+        int len = strlen(id)+strlen(dev->port->path)+2;
+        char *ret = g_malloc(len);
+        snprintf(ret, len, "%s/%s", id, dev->port->path);
+        return ret;
+    } else {
+        return g_strdup(dev->port->path);
+    }
 }
 
 static char *usb_get_fw_dev_path(DeviceState *qdev)