16.3. USB Devices

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This section gives the commands required for handling USB devices.

16.3.1. Assigning USB Devices to Guest Virtual Machines

Most devices such as web cameras, card readers, disk drives, keyboards, mice are connected to a computer using a USB port and cable. There are two ways to pass such devices to a guest virtual machine:
  • Using USB passthrough - this requires the device to be physically connected to the host physical machine that is hosting the guest virtual machine. SPICE is not needed in this case. USB devices on the host can be passed to the guest in the command line or virt-manager. See Section 19.3.2, “Attaching USB Devices to a Guest Virtual Machine” for virt manager directions. Note that the virt-manager directions are not suitable for hot plugging or hot unplugging devices. If you want to hot plug/or hot unplug a USB device, see Procedure 20.4, “Hot plugging USB devices for use by the guest virtual machine”.
  • Using USB re-direction - USB re-direction is best used in cases where there is a host physical machine that is running in a data center. The user connects to his/her guest virtual machine from a local machine or thin client. On this local machine there is a SPICE client. The user can attach any USB device to the thin client and the SPICE client will redirect the device to the host physical machine on the data center so it can be used by the guest virtual machine that is running on the thin client. For instructions via the virt-manager see Section 19.3.3, “USB Redirection”.

16.3.2. Setting a Limit on USB Device Redirection

To filter out certain devices from redirection, pass the filter property to -device usb-redir. The filter property takes a string consisting of filter rules, the format for a rule is:
Use the value -1 to designate it to accept any value for a particular field. You may use multiple rules on the same command line using | as a separator. Note that if a device matches none of the passed in rules, redirecting it will not be allowed!

Example 16.1. An example of limiting redirection with a guest virtual machine

  1. Prepare a guest virtual machine.
  2. Add the following code excerpt to the guest virtual machine's' domain XML file:
        <redirdev bus='usb' type='spicevmc'>
          <alias name='redir0'/>
          <address type='usb' bus='0' port='3'/>
          <usbdev class='0x08' vendor='0x1234' product='0xBEEF' version='2.0' allow='yes'/>
          <usbdev class='-1' vendor='-1' product='-1' version='-1' allow='no'/>
  3. Start the guest virtual machine and confirm the setting changes by running the following:
    #ps -ef | grep $guest_name
    -device usb-redir,chardev=charredir0,id=redir0,/
  4. Plug a USB device into a host physical machine, and use virt-manager to connect to the guest virtual machine.
  5. Click USB device selection in the menu, which will produce the following message: "Some USB devices are blocked by host policy". Click OK to confirm and continue.
    The filter takes effect.
  6. To make sure that the filter captures properly check the USB device vendor and product, then make the following changes in the host physical machine's domain XML to allow for USB redirection.
          <usbdev class='0x08' vendor='0x0951' product='0x1625' version='2.0' allow='yes'/>
          <usbdev allow='no'/>
  7. Restart the guest virtual machine, then use virt-viewer to connect to the guest virtual machine. The USB device will now redirect traffic to the guest virtual machine.
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