Re: [Qemu-discuss] Issue of usb emulation with qemu

[Mike Lovell]

On 04/09/2012 06:42 AM, tangming wrote:
> Recentlly I have an usb emulation issue with qemu. There is one usb device on 
> host, and now I need this usb device to be used by several VMs.
> I enable the usb emulation with the VMs' qemu parameter "-usbdevice 
> host:xxxx:xxxx", with individual qemu instance for each vm.
> but seems that only one vm can use this usb normally.
>
> Is there any way to share the emulated usb device with two or more VMs?
> Any suggestions will be appreciated,

i don't think this is possible. the way usb is designed, there is a host 
controller and one or more devices connected to it. the systems assumes 
only one host controller talks to devices. in a set up where there would 
be multiple guests talking to the same usb device, this would break. how 
would the device know which host to respond to or send data to? there 
are devices for sale that claim to share usb devices over a network. but 
these only allow one host to be talking to a given usb device at a time 
and use some locking to prevent otherwise. this is why i don't think its 
going to be possible.

you may be able to have the usb device get passed around to various 
guests without restarting the guests by hot adding and hot removing the 
device. but it will require something external to qemu to co-ordinate that.

hope that helps.

mike