问创建libvirt KVM域时报错:无效参数:无法获得/usr/libexec/qemu type=kvm的首选机器

EN

<domain type="kvm">
    <name>clara</name>
    <memory unit="MiB">4096</memory>
    <vcpu>2</vcpu>
    <os>
        <type>hvm</type>
        <boot dev="hd"></boot>
    </os>
    <features>
        <pae></pae>
        <acpi></acpi>
        <apic></apic>
    </features>
    <cpu></cpu>
    <devices>
        <disk type="volume" device="disk">
            <driver name="qemu" type="qcow2"></driver>
            <source pool="default" volume="clara-rootfs"></source>
            <target dev="vda" bus="scsi"></target>
            <wwn>05abcd62857fe8f1</wwn>
        </disk>
        <disk type="file" device="cdrom">
            <driver name="qemu" type="raw"></driver>
            <source file="/var/lib/libvirt/images/cloudinit.clara.iso"></source>
            <target dev="hdd" bus="ide"></target>
        </disk>
        <controller type="scsi" model="virtio-scsi"></controller>
        <interface type="bridge">
            <mac address="E2:F5:2A:A9:4A:42"></mac>
            <source bridge="bridge0"></source>
            <model type="virtio"></model>
        </interface>
        <channel type="unix">
            <target type="virtio" name="org.qemu.guest_agent.0"></target>
        </channel>
        <graphics type="spice" autoport="yes"></graphics>
        <rng model="virtio">
            <backend model="random">/dev/urandom</backend>
        </rng>
    </devices>
</domain>

# virsh define clara.xml 
error: Failed to define domain from clara.xml
error: invalid argument: could not get preferred machine for /usr/libexec/qemu-kvm type=kvm