Re: [Libvir] [PATCH] check the maximum of virtual CPU

On Mon, Mar 05, 2007 at 03:42:35PM +0900, Masayuki Sunou wrote: I was thinking about how to make use of this new API in virt-manager when I came up with a further complication :-) There are three scenarios where I'd like to be able to find out the maximum VCPUs possible for a guest VM: 1. When initially creating a VM 2. When changing the config of an inactive VM 3. When changing the config of a running VM Thus far in this thread, we've focused on addressing the last point, but I think its worth trying address all 3 while we're looking at this area. In the first case, we do not have a virDomainPtr object at all yet, all we have is a virConnectPtr and info about the type of domain we're planning to create - Xen, QEMU, KVM, KQEMU. When creating a VM we need to apply some domain type specific limit. In the case of an inactive domain, we have a virDomainPtr object and from that the internal drivers can determine the domain type or Xen, QEMU, KVM, etc, and again apply some domain type specific limit. In the 3rd case of a running VM though, the hypervisor limit is typically not neccessarily the one that is relevant. While the hypervisor will still has its own limit of VCPUs, the effective limit is likely lower - ie fixed at the number of virtual CPUs which were allocated when the guest OS booted. So if you boot a guest with 4 cpus, you can hotplug remove & add CPUs, but you can never go above 4 until the guest is shutdown. So anyway, I think we need to add 2 apis to address this whole issue: - int virConnectGetMaxVcpus(virConnectPtr conn, const char *type); Returns the maximum number of virtual CPUs supported for a guest VM of a specific type. Thje 'type' parameter here corresponds to the 'type' attribute in the <domain> element of the XML. - int virDomainGetMaxVcpus(virDomainPtr dom); Returns the maximum number of virual CPUs supported for the guest VM. If the guest is inactive, this is basically the same as virConnectGetMaxVcpus. If the guest is running this will reflect the maximum number of VCPus the guest was booted with. In terms of the Xen implementation, the virConnectGetMaxVcpus method can simply return MAX_VIRT_VCPUS. Likewie virDomainGetMaxVcpus can do the same for inactive guests, but if the guest is running then we will need to call out to XenD to extract the max vcpus info. Any other thoughts from people on the list ??? Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|