On Mon, Apr 16, 2012 at 12:34 PM, Kevin Wolf <kw...@redhat.com> wrote: > Am 13.04.2012 12:30, schrieb Stefan Hajnoczi: >> On Thu, Apr 12, 2012 at 4:01 PM, Kevin Wolf <kw...@redhat.com> wrote: >>> The remaining space between the end of the header extension area and the >>> end of >>> -the first cluster can be used for other data. Usually, the backing file >>> name is >>> -stored there. >>> +the first cluster can be used for the backing file name. It is not allowed >>> to >>> +store other data here, so that an implementation can safely modify the >>> header >>> +and add extensions without harming data of compatible features that it >>> +doesn't support. Compatible features that need space for additional data >>> can >>> +use a header extension. >> >> Does this change the spec for qcow2 version 2? Previously anything >> could be after the header extension area, now this has been changed so >> only the backing filename is allowed (for safe modification). In >> practice this should be okay but in theory I think this is changes the >> qcow2 version 2 semantics. > > I guess it does. Are you aware of anyone using this? We could in theory > add the restriction only for version 3+, but I'd rather avoid special > cases if possible. > > I think in practice even the old qcow2 implementation would break images > if you put arbitrary data there.
I'm not aware of anything that uses it. Stefan
