Though in Debian Stretch the current implementation for creating images, mounting them and writing to them works, it does not in Buster with recent qemu versions.
But, as it turns out, there are two fixes that now seem to remedy this.
flock seems to cause a timeout when used on a NBD device.
Creating a VDI image needs to have -o static=on in place. Without it, there will be a kernel panic.
Though in Debian Stretch the current implementation for creating images, mounting them and writing to them works, it does not in Buster with recent qemu versions.
But, as it turns out, there are two fixes that now seem to remedy this.
flockseems to cause a timeout when used on a NBD device.-o static=onin place. Without it, there will be a kernel panic.