Am 15.01.2018 um 14:51 hat Daniel P. Berrange geschrieben: > On Mon, Jan 15, 2018 at 02:38:48PM +0100, Kevin Wolf wrote: > > Am 12.01.2018 um 11:53 hat Daniel P. Berrange geschrieben: > > > On Thu, Jan 11, 2018 at 08:52:17PM +0100, Kevin Wolf wrote: > > > > Signed-off-by: Kevin Wolf <kw...@redhat.com> > > > > --- > > > > qapi/block-core.json | 33 ++++++++++++++++++++++++++++++++- > > > > 1 file changed, 32 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/qapi/block-core.json b/qapi/block-core.json > > > > index 1749376c61..9341f6708d 100644 > > > > --- a/qapi/block-core.json > > > > +++ b/qapi/block-core.json > > > > @@ -3320,6 +3320,37 @@ > > > > { 'command': 'blockdev-del', 'data': { 'node-name': 'str' } } > > > > > > > > ## > > > > +# @BlockdevQcow2CompatLevel: > > > > +# @0_10: The original QCOW2 format as introduced in qemu 0.10 > > > > (version 2) > > > > +# @1_1: The extended QCOW2 format as introduced in qemu 1.1 > > > > (version 3) > > > > +# > > > > +# Since: 2.10 > > > > +## > > > > +{ 'enum': 'BlockdevQcow2CompatLevel', > > > > + 'data': [ '0_10', '1_1' ] } > > > > + > > > > + > > > > +## > > > > +# @BlockdevCreateOptionsQcow2: > > > > +# > > > > +# Driver specific image creation options for qcow2. > > > > +# > > > > +# TODO Describe fields > > > > +# > > > > +# Since: 2.12 > > > > +## > > > > +{ 'struct': 'BlockdevCreateOptionsQcow2', > > > > + 'data': { 'size': 'size', > > > > + '*compat': 'BlockdevQcow2CompatLevel', > > > > + '*backing-file': 'str', > > > > + '*backing-fmt': 'BlockdevDriver', > > > > > > For anything non-trivial, the caller is going to have to stuff a > > > JSON string into 'backing-file' value. It feels like we should > > > be referencing 'BlockdevOptions' here in some manner. > > > > Hm, that's an interesting question. For the image creation, this is > > really treated as a string that is directly written into the image file, > > without being parsed, so 'str' is the more correct type in this context. > > However, when the backing file gets loaded, that string is in fact > > parsed and we expect it to describe the same thing as BlockdevOptions. > > > > If we get BlockdevOptions here, qemu would have to convert them into a > > json:{...} string before writing the header of the new image. > > Compatibility code would become a bit more complex because we'd have to > > convert the existing string into BlockdevOptions, only to convert it > > back to a string before we write it to the image file. And finally, the > > 1023 character limit of qcow2 becomes kind of unpredicatble when you > > don't pass the string yourself. > > > > So considering all of that, I still think that 'str' is the better > > option here. > > Hmm, when we write the backing chain into the qcow2 header, we only > want to write the 1st level of the backing chain.
That's a good point, too. References in BlockdevOptions are often mandatory, which conflicts with this. > When we are creating the new qcow2 image, we could be pointing to a backing > chain that goes many levels deep. So the actual creation process potentially > needs to be given the full arbitrarily deep backing file eg in order that > we can set 'encrypt.secret' for any encrypted images at at arbitrary level. But we don't even access the images in the backing chain during image creation. Why would we need a secret for them? > IOW, I think we need to be able to pass BlockdevOptions here to specify the > full deep chain, but then only the 1st level of these BlockdevOptions should > get written into the qcow2 file header. But what's the point of even passing the full chain if only the first layer is actually used? Kevin