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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 02 Jun 2014 09:36:20 +0200
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Subject: Re: [Qemu-devel] [PATCH 1/6] usb: add usb_bus_release function
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To: arei.gonglei@huawei.com
Cc: weidong.huang@huawei.com, luonengjun@huawei.com, qemu-devel@nongnu.org, peter.huangpeng@huawei.com

  Hi,

> +void usb_bus_release(USBBus *bus)
> +{
> +    assert(next_usb_bus > 0);
> +
> +    next_usb_bus--;
> +    QTAILQ_REMOVE(&busses, bus, next);
> +}

That breaks when not hotplugging in last-in-first-out order.  I'd
suggest to simply leave next_usb_bus alone on unplug.  It is only used
for bus numbering.  We'll get holes in our bus numbering then, but we
can't avoid that with hotplug anyway.

cheers,
  Gerd