[libvirt] How libvirt address qemu command line args

Now I want to add some args about TPM to domain's XML,so I can start a domain by virt-manager or other virsh command,and then ,I would like to use sVIrt security context to label vTPM and correspondingVM,But I do not know how to get these XML args in libvirt. the key problem is that how can i get and recognize these args!!! related XML content : <qemu:commandline> <qemu:arg value='-enable-kvm'/> <qemu:arg value='-drive'/> <qemu:arg value='file=/root/nvram_2.0-jin.qcow2,if=none,id=nvram0-0-0,format=qcow2'/> <qemu:arg value='-device'/> <qemu:arg value='tpm-tis,tpmdev=tpm-tpm0,id=tpm0'/> <qemu:arg value='-tpmdev'/> <qemu:arg value='libtpms,id=tpm-tpm0,nvram=nvram0-0-0,startup=clear'/> <qemu:arg value='-bios'/> <qemu:arg value='/root/xenSeabios/out/bios.bin'/> </qemu:commandline> zhunxun(a)gmail.com