USB

crosvm supports attaching USB devices from the host by emulating an xhci backend.

Unlike some other VM software like qemu, crosvm does not support attaching USB devices at boot time, however we can tell the VM to attach the devices once the kernel has booted, as long as we started crosvm with a control socket (see the control socket section in advanced usage).

First, start crosvm making sure to specify the control socket:

$ crosvm run -s /run/crosvm.sock ${USUAL_CROSVM_ARGS}

Then, you need to identify which device you want to attach by looking for its USB bus and device number:

$ lsusb
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 022: ID 18d1:4ee7 Google Inc. Pixel 5
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Assuming in this example the device you want is the Google Inc. Pixel 5, its bus and port numbers are 002 and 022 respectively.

There should be a USB device file on the host at the path /dev/bus/usb/002/022 which is what you want to pass to the crosvm usb attach command:

# crosvm usb attach 00:00:00:00 /dev/bus/usb/002/022 /run/crosvm.sock

You can run this command as root or make sure your current user has permissions to access the device file. Also make sure the device is not currently attached to any other drivers on the host and is not already in use.

NOTE: You need to pass some string formatted like 00:00:00:00 as the first parameter to the usb attach command. This is a deprecated argument and is not used by crosvm, but we need to include it anyway for it to work. It will be removed in the future.

On the host you should see a message like:

ok 9

Which tells you the operation succeeded and which port number the USB device is attached to (in this case 9).

Inside the VM you should see dmesg messages that the USB device has been attached successfully and you should be able to use it as normal.

If you want to detach the device, simply issue a detach command to the same number as the port returned by the attach command:

# crosvm usb detach 9 /run/crosvm.sock

Which should return another ok 9 confirmation.

Keep in mind that when a USB device is attached to a VM, it is in exclusive mode and cannot be used by the host or attached to other VMs.