After setting up windows vm with GPU passthrough and looking glass I realized that you can’t drag and drop files into looking glass window like you could with other Spice clients.
I couldn’t see anyone request this functionality in looking glass neither on level1forums not on github issues - perhaps this method isn’t very popular (or maybe it’s less secure that other filesystem sharing methods in libvirt).
However, it’s really convenient not having to set up a shared folder and just drop files on demand.
The problem was that I had to disable QXL device when using GPU Passthrough with looking glass - otherwise it would disable mouse for looking glass (if anyone knows any workarounds please let me know).
I was surproised to find out though that you can still open a spice client (virt-viewer or virt-manager) and drag and drop files all the same - it still works even without a monitor (a QXL device).
Maybe someone know if there is a command line program to initiate these transfers? It might be useful for larger amounts of files.
If there are any security concerns with spice file sharing please let me know.
UPDATE: this “technique” comes in handy not only for transferring files with looking glass - if you clipboard stops working when using an external monitor to output display of your vm and you are passing through your mouse and keyboard via evdev passthrough having that Spice client window opened is the only way I could find to share clipboard.