Re: [libvirt] [RFC] virDomain{Attach,Detach}Device

History I found that virDomainDetachDevice did not work with inactive domains and submitted a patch [1] to fix this. As it turns out, some drivers do not support attaching/detaching devices on inactive domains and it was preferred that virDomain{Attach,Detach}Device only be permitted on active domains. I posted a follow-up patch [2] that restricted virDomain{Attach,Detach}Device to active domains only, although as Daniel Veillard pointed out this restriction should have been enforced in the libvirt front-end. Cole Robinson suggested improving virsh [3] to handle the case of inactive vs. active by redefining the domain with new device (or removed device) when domain is inactive. While implementing this improvement I asked some questions on IRC that resulted in another approach suggested by Dan Berrange as outlined below. Introduce two new APIs virDomainAttachDeviceFlags(virDomainPtr dom, const char *xml, unsigned flags) virDomainDetachDeviceFlags(virDomainPtr dom, const char *xml, unsigned flags) with flags being one or more from VIR_DOMAIN_DEVICE_ATTACH_CURRENT, VIR_DOMAIN_DEVICE_ATTACH_LIVE, VIR_DOMAIN_DEVICE_ATTACH_CONFIG. (I'm not sure about the ATTACH in these names. Perhaps CHANGE or MODIFY would be more appropriate.) If caller specifies CURRENT (default), add or remove the device depending on the current state of domain. E.g. if domain is active add or remove the device to/from live domain, if it is inactive change the persistent config. If caller specifies LIVE, only change the active domain. If caller specifies CONFIG, only change persistent config - even if the domain is active. If caller specifies both LIVE and CONFIG, then change both. If a driver could not satisfy the exact requested flags it must return an error. E.g if user specified LIVE but the driver can only change live and persisted config, the driver must fail the request. The existing virDomain{Attach,Detach}Device would be declared to be equivalent to virDomain{Attach,Detach}DeviceFlags(LIVE). Finally, virsh {attach,detach}-{disk,interface,device} would be modified to add a --persistent flag in order to set the appropriate flags when calling the new APIs.