Re: [Qemu-devel] [RFC] Plan for moving forward with QOM

[Anthony Liguori]

On 09/14/2011 04:15 PM, Jan Kiszka wrote:
> On 2011-09-14 21:42, Anthony Liguori wrote:
> > > Such names can get fairly long I'm afraid...
> >
> > A user should never even see these names.  A user probably will always
> > interact with devices via paths.
>
> Right.
> <scratching head>
> But will those automatic names be used at all then?

Yes, because QEMU is not going to know anything about path names :-)

Path names should be a concept that exists entirely in the client.  That may be 
HMP or that may be a command line tool (like the proposed qemu script).

The only management interface exposed to the client is:

create_object(type, name)
value = get_object_property(name, property_name)
void set_object_property(name, property_name, value)
props = list_object_properties(name)
names = list_objects()

So names are very important from a QMP perspective, but not something users 
every really see.

> > We can also look at doing things like user-defined aliases or something
> > like that.
>
> ...or a way to set the name of an auto-generated device via its pathname.

The auto-generated name is already basically generated from a pathname.  But 
that path isn't necessarily the obvious one from a user's point of view.

> > > > Since a bus is-a device in QOM, there is no notion of having multiple
> > > > busses
> > > > under the same device.  A device can implement multiple bus interfaces,
> > > > but can
> > > > only be a single bus of any given bus interface.
> > > >
> > > > Device names are completely independent of pathnames.  For devices that
> > > > are no
> > > > user created, device names should be treated as opaque blobs with
> > > > absolutely no
> > > > semantic meaning.
> > > >
> > > > All device relationships are identified as named properties.  A QOM path
> > > > name
> > > > consists of a named device,
> > >
> > > With a system root device called '/'. So '/' is another
> > > character(-sequence) that is forbidden in device names.
> >
> > Yes, but there is no system root device.
>
> There is always a generic link to some root device. I think it would be
> more regular to make that link an abstract device called '/' - maybe
> even one that can hold a larger number of children. Keeps the door open
> for crazy multi-root systems models.

From a client perspective, yes.  The scripts I showed at KVM Forum had '/' 
return the list of all user-created devices as the contents.  It's a nice 
feature but I think it's something that lives in a client, not in the object model.

Regards,

Anthony Liguori

> Jan