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

From: Mike Lovell
Subject: Re: [Qemu-discuss] Issue of usb emulation with qemu
Date: Thu, 12 Apr 2012 12:47:38 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20120313 Lightning/1.0b2 Thunderbird/3.1.20

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.


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