于 2013-7-18 13:43, Stefan Hajnoczi 写道:
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.