EDIT: this is now fixed.
Adding a usb redirector in virt-manager solved the problem very simply. So one must not add manually the usb device in virt-manager. I also had crashes befopre if I try to add a mouse manually as a usb device.
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I could use a usb microphone before, in a windows guest, with kvm. But now I cannot and I don't know what changed. It used to work plug and play.
Since it does not work, I found I can add it manually in virt-manager, I can see the device with the manufacturer name,
then if I open a program about to use it or the windows sound settings, the VM crashes with the following log.
I get this in /var/log/libvirt/qemu.log
qemu-system-x86_64: /build/qemu-oK652D/qemu-3.1+dfsg/hw/usb/host-libusb.c:819: usb_host_ep_update: Assertion `udev->altsetting < conf->interface.num_altsetting' failed.
2020-12-01 09:20:38.916+0000: shutting down, reason=crashed
lsusb finds the device:
Bus 001 Device 006: ID 0909:0051 Audio-Technica Corp.
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What does this assertion check?
https://github.com/qemu/qemu/blob/maste ... t-libusb.c
for (i = 0; i < conf->bNumInterfaces; i++) {
assert(udev->altsetting < conf->interface.num_altsetting);
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