Dear Fil,
I am not sure if my answer can help you.
I had ever asked a similar question to Daniel and I was using a thirty-party
card. As a container uses a shared kernel with the host, so hostdev
mode='subsystem' doesn't make sense. Maybe you can try to use hostdev
mode='capabilities'. Please see
http://libvirt.org/formatdomain.html#elementsHostDevCaps
Actually mode='subsystem' is *IS* fully supported for USB devices. It is
only PCI devices where it is not available with LXC.
Regards,
Daniel
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