On Mon, Sep 19, 2016 at 02:19:19PM +0200, Paolo Bonzini wrote:
> On 19/09/2016 14:12, Daniel P. Berrange wrote:
> > On Mon, Sep 19, 2016 at 12:58:30PM +0100, Daniel P. Berrange wrote:
> >> The current -object command line syntax only allows for
> >> creation of objects with scalar properties, or a list
> >> with a fixed scalar element type. Objects which have
> >> properties that are represented as structs in the QAPI
> >> schema cannot be created using -object.
> >>
> >> This is a design limitation of the way the OptsVisitor
> >> is written. It simply iterates over the QemuOpts values
> >> as a flat list. The support for lists is enabled by
> >> allowing the same key to be repeated in the opts string.
> >>
> >> It is not practical to extend the OptsVisitor to support
> >> more complex data structures while also maintaining
> >> the existing list handling behaviour that is relied upon
> >> by other areas of QEMU.
> >>
> >> Fortunately there is no existing object that implements
> >> the UserCreatable interface that relies on the list
> >> handling behaviour, so it is possible to swap out the
> >> OptsVisitor for a different visitor implementation, so
> >> -object supports non-scalar properties, thus leaving
> >> other users of OptsVisitor unaffected.
> > 
> > Urgh, I've just discovered that this is not in fact true.
> > 
> > The 'memory-backend' object type uses uint16List which
> > has the hacky list syntax
> > 
> >   -object memory-backend-ram,\
> >           id=ram-node2,size=24578621440,policy=bind,\
> >           host-nodes=1-2,host-nodes=5,host-nodes=7,
> > 
> > So I'll need to figure out a way to preserve this syntax...
> Is there a usecase for qdict_crumple without the following
> de-stringification pass?  If not, qdict_crumple could use a
> StringInputVisitor on the values directly.

I'm not sure I understand how that would help and in any case, the
string-input-visitor itself is incapable of dealing with compound
properties. It too could/should be ultimately replaced by the
qobject-input-visitor combined with a pre-processing step to
turn the input string into a qdict.

The problem I'm facing with the above scenario though occurs
before we get anywhere near the visitors, or the crumple step.

When qemu_opts_to_qdict() turns QemuOpts into QDict, it looses
repeated options. So given a command line

   -object memory-backend-ram,\

we're getting an initial QDict containing


What I need to do is make qemu_opts_to_qdict more intelligent
so that if it sees repeated strings, it inserts them into the
qdict using list index style. eg, the QemuOpts -> QDict
conversion should have at minimum given us


although even then there's some magic in the range value seen there. I'm
unclear on whether we should try to deal with the range "1-2" in the
qemu_opts_to_qdict() method, the qdict_crumple() method or the qobject
input visitor code for parsing ints.

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