[libvirt] Live migration using virsh

Sir, I am working in cloud environment and i have set up a private cloud using eucalyptus. I am trying to migrate virtual machines within the cloud using virsh migrate command. I could successfully implement it but when i wanted to know the method used to do live migration. I tried to interpret the code. I also saw that they are setting a flag initially if it is live migration and then assigning 1 to variable live. and i also could find that xenDomainMigratePrepare is calling xend_op which in turn is calling xend_op_ext. But i could'n understand the method of migration. Can you please explain the logic?