gistfile1.txt

#!/bin/bash -
i=0
while [ $# -gt 0 ]; do
    case "$1" in
        -append)
            shift;
            CMDLINE="$1";
            shift;;
        *)
            args[i]="$1"
            (( i++ ))
            shift ;;
    esac
done

set -x
if [ -z "$CMDLINE" ]; then
    exec kvm "${args[@]}"
fi

CMDLINE="root=9proot rootfstype=9p rootflags=trans=virtio,version=9p2000.L,cache=loose $CMDLINE"

sudo mkdir -p /mnt/guestfs
sudo mount -o loop /var/tmp/.guestfs-1000/appliance.d/root /mnt/guestfs
exec kvm \
    -fsdev local,id=root,path=/mnt/guestfs/,security_model=none \
    -device virtio-9p-pci,fsdev=root,mount_tag=9proot \
    --append "$CMDLINE" "${args[@]}"