Re: [Qemu-devel] [PATCH 0/4] export internal snapshot by qemu-nbd

[Fam Zheng]

On Fri, 07/19 17:03, Wenchao Xia wrote:
> 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.
> 
Is the VMDK snapshot internal? Which subformat of VMDK do you mean here?

Thanks.

-- 
Fam