[libvirt-users] Some question about code of xenapi

Hello, guys! I am doing some experiment to control XenServer with libvirt, when I define a domain, it always fails and gives the following message: error: Failed to define domain from /root/new.xml error: internal error: Couldn't get VM information from XML so I diving into the souce and found it always fails at network creating, and the code in libvirt-1.3.5\src\xenapi\xenapi_utils.c, line 437 is following: xen_vif_create(session, &vif, vif_record); if (!vif) { xen_vif_free(vif); xen_vif_record_free(vif_record); xen_network_record_free(net_rec); xen_network_set_free(net_set); return 0; } xen_vif_record_free(vif_record); xen_network_record_free(net_rec); ... ... return -1; should this if be if (vif) {...}, if the vif is null, why need to free it?