Hi, all when I use (python API) setMemoryParameters with flags= VIR_DOMAIN_AFFECT_CONFIG|VIR_DOMAIN_AFFECT_LIVE , an error occurs as follow: (libvirt 1.2.4) libvirt: error : flags 'affect live' and 'affect config' in virDomainGetMemoryParameters are mutually exclusive I check the function libvirt_virDomainSetMemoryParameters in libvirt-override.c and find the code below: Line 1204-1206: LIBVIRT_BEGIN_ALLOW_THREADS; i_retval = virDomainGetMemoryParameters(domain, NULL, &nparams, flags); LIBVIRT_END_ALLOW_THREADS; Line 1220-1222: LIBVIRT_BEGIN_ALLOW_THREADS; i_retval = virDomainGetMemoryParameters(domain, params, &nparams, flags); LIBVIRT_END_ALLOW_THREADS; Function virDomainGetMemoryParameters doesn't support flags VIR_DOMAIN_AFFECT_CONFIG|VIR_DOMAIN_AFFECT_LIVE. So the error above occurs. The first call of virDomainGetMemoryParameters is to "cause @nparams on output to contain the number of parameters supported by the hypervisor". And what's the role of the second call? Maybe, so do other functions such as *libvirt_virDomainSetSchedulerParameters, *libvirt_virDomainSetBlkioParameters In commit 56cec18d761a1f99862c43811de60380c65881e6. IMHO, an example flag (such as VIR_DOMAIN_AFFECT_CONFIG) can be used in virDomainGetMemoryParameters just to get something from hypervisor rather than @flags which is a parameter of setMemoryParameters .