From: Anthony Liguori [mailto:anthony@codemonkey.ws] Sent: Wednesday, August 10, 2011 10:28 PM To: Avi Kivity Cc: Blue Swirl; Stefan Hajnoczi; Shribman, Aidan; qemu-devel Developers; libvir-list@redhat.com Subject: Re: [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of large memory apps
a) A query-migration-caps command that returns a dict with two lists of strings. Something like:
{ 'execute': 'query-migration-caps' } { 'return' : { 'capabilities': [ 'xbzrle' ], 'current': [] } }
b) A set-migration-caps command that takes a list of strings. It simply takes the intersection of the capabilities set with the argument and sets the current set to the result. Something like:
{ 'execute': 'set-migration-caps', 'arguments': { 'set': [ 'xbzrle' ] }} { 'return' : {} }
We may want to further sub-divide capabilities into categories: { 'execute': 'query-migration-caps' } { 'return' : { 'encoding' : { 'current', 'asn.1', 'proto2', 'thrift', etc. } }, { 'delta' : { 'xbzrle', "xdelta", ...} }, { 'compression' : { 'snappy', 'lzo' } } } This would help libvirt/management to select features automatically or manually (via UI) without having to 'understand' the any given capability meaning.
Yes. But that negotiation needs to become part of the "protocol" for migration. In the absence of that negotiation, we need to use the wire protocol we use today. We cannot have ad-hoc feature negotiation for every change we make to the wire protocol.
Agreed. Therefore caps plus xbzrle could be added before ASN.1/v1.0 without breaking anything as long as when 'set-migration-caps' is not issued Qemu uses the current protocol. Aidan