Comment 80 for bug 156085

On Fri, 2008-12-19 at 13:57 +0000, Daniele Smartango wrote:
> I tried it in Intrepid forcing dependencies, I got:
>
> (qemu) usb_add host:0951:1601
> husb: open device 2.5
> /dev/bus/usb/002/005: Permission denied

Daniele, see the discussion on device-node permissions further back
(2008-09-04 onwards).

The unresolved issue is, no decision has been made on how to set
permissions for KVM/QEMU to access the raw device nodes. By default they
are root:root so when KVM/QEMU are run as a regular user the "Permission
Denied" message is to be expected.

Running KVM/QEMU as root isn't the most desirable solution either.

Until a decision is made on how best to support this the user will need
to choose a method to set permissions manually to allow the user access
to the raw devices.

In my PPA package I added manual instructions to the man-page. I'll
quote it here (Dustin - maybe this is worth adding to the current
lvm/qemu man pages until the permissions issue is resolved?):

USING USB DEVICES
       kvm-74 introduced much-improved support for USB host devices, but still expected to find
       them in /proc/bus/usb/ which has been deprecated for over a year. The Ubuntu patches added
       in 1:74+dfsg-0ubuntu2 provide support for /sys/bus/usb/devices/ and /dev/bus/usb/devices
       discovery, and connection via /dev/bus/usb/*/*

       kvm must be started with the "-usb" option. From the kvm monitor console (Ctrl+Alt+2 when
       the VM Window has grabbed focus - Ctrl+Alt+1 to return to the VM) USB host devices can be
       discovered using:

       info usbhost

       The devices can be added to the guest using, for example:

       add_usb host:5.3

       If the guest is running as non-root the permissions to /dev/bus/usb/*/* will need altering
       to allow the VM read/write access to the USB devices.

       Create a new group "vm" and add users that require USB access for VMs to it:

       sudo addgroup vm
       sudo addgroup $USER vm

       Log-out/log-in to effect the new group membership.

       Add a udev rule to assign USB devices to the vm group:

       # Virtual Machine hypervisor access to USB devices
       SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", GROUP="vm"
       SUBSYSTEM=="usb_device", GROUP="vm"

       Save the file as /etc/udev/rules.d/41-vm-usb.rules and reload udevd:

       sudo /etc/init.d/udev restart

       The guest virtual machines should now be able to access the USB devices without root priv‐
       ileges.