On Fri, 07/19 17:03, Wenchao Xia wrote: > δΊ 2013-7-18 13:43, Stefan Hajnoczi ει: > >On Wed, Jul 17, 2013 at 10:03:51PM +0800, Wenchao Xia wrote: > >>This series allow user to read internal snapshot's contents without qemu-img > >>convert. Another purpose is that, when qemu is online and have taken an > >>internal snapshot, let user invoke qemu-nbd to do any thing on it except > >>write. > > > >I agree with Eric and Kevin that we cannot access image files while QEMU > >has them open. > > > >A bit more detail about using the run-time NBD server to do this safely: > > > >Internal snapshots are not first-class block layer objects today. They > >are not BlockDriverStates, instead you must access their data through > >bdrv_snapshot_goto() or bdrv_snapshot_load_tmp(). > > > Also cc to Fam Zheng an Kevin: > I think BlockDriverStates modification, is based on a more basic > question: does qcow2's data structure on disk, allow multiple snapshot > reader, while one active writer, without lock? I think the modification > showed above, already said "yes" to this question. If yes, just > create a new BlockDriverStates, we should say yes in spec. > I wonder how vmdk allow direct snapshot access by VixDiskLib 1.1, > without network expense on host, it should be the format said support > of it. > Is the VMDK snapshot internal? Which subformat of VMDK do you mean here?
Thanks. -- Fam
