花の様に

virDomainDefParseXML -> virDomainDiskDefParseXML -> virDomainDeviceInfoParseXML -> virDomainDeviceAddressParseXML -> virPCIDeviceAddressParseXML

if (devaddr) {
    if (virDomainParseLegacyDeviceAddress(devaddr,
                                          &def->info.addr.pci) < 0) {
        virReportError(VIR_ERR_INTERNAL_ERROR,
                       _("Unable to parse devaddr parameter '%s'"),
                       devaddr);
        goto error;
    }
    def->info.type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI;
} else {

qemuDomainSaveInternal ->

if (!(cookie = qemuDomainSaveCookieNew(vm)))
    goto endjob;

if (!(data = virQEMUSaveDataNew(xml, cookie, was_running, compressed,
                                driver->xmlopt)))
    goto endjob;
xml = NULL;

ret = qemuDomainSaveMemory(driver, vm, path, data, compressedpath,
                           flags, QEMU_ASYNC_JOB_SAVE);
if (ret < 0)
    goto endjob;

/* Shut it down */
qemuProcessStop(driver, vm, VIR_DOMAIN_SHUTOFF_SAVED,
                QEMU_ASYNC_JOB_SAVE, 0);

        rc = qemuMonitorMigrateToFd(priv->mon,
                                    QEMU_MONITOR_MIGRATE_BACKGROUND,
                                    fd);
                                    
int
qemuMonitorMigrateToFd(qemuMonitorPtr mon,
                       unsigned int flags,
                       int fd)
{
    int ret;
    VIR_DEBUG("fd=%d flags=0x%x", fd, flags);

    QEMU_CHECK_MONITOR(mon);

    if (qemuMonitorSendFileHandle(mon, "migrate", fd) < 0)
        return -1;

    ret = qemuMonitorJSONMigrate(mon, flags, "fd:migrate");

    if (ret < 0) {
        if (qemuMonitorCloseFileHandle(mon, "migrate") < 0)
            VIR_WARN("failed to close migration handle");
    }

    return ret;
}

qemu should support sendFD (qemu is should using a unix socket monitor)

qemu monitor get fd (SCM_RIGHTS)

SCM_RIGHTS
Send or receive a set of open file descriptors from
another process. The data portion contains an integer
array of the file descriptors.

/* Perform the migration */
if (qemuMigrationSrcToFile(driver, vm, fd, compressedpath, asyncJob) < 0)
    goto cleanup;

qemuMonitorJSONMigrate