Re: [Qemu-devel] [RFC] Machine description as data

[Markus Armbruster <armbru@redhat.com>]

Ian Jackson <Ian.Jackson@eu.citrix.com> writes:

> Markus Armbruster writes ("[Qemu-devel] [RFC] Machine description as data"):
>> [stuff]
>
> Yes, this is a good approach.  I have one question though:
>
>>    Define an internal machine configuration data structure.  Needs to be
>>    sufficiently generic to be able to support even oddball machine
>>    types.  Make it a decorated tree, i.e. a tree of named nodes with
>>    named properties.
>
> Many real systems are not strictly tree-structured, because there are
> hardware devices which connect via several different paths.  For
> example, much hardware supported by OpenWRT comes with a built-in
> bridge chip connected internally to a hidden ethernet card; a tape
> library would have one interface for the robot and a bunch of SCSI
> tapereaders; etc.
>
> When an emulation of such a device starts up, it will want to bind to
> several parents.  How will you represent this ?
>
> Ian.

Generalize the tree to a a directed acyclic graph (DAG)?

Got that already, in fact, only the non-tree edges are second-class
citizens.  They are separate from tree edges, and unlike those, they can
only be added by the config() methods.  Maybe it would be easier and
cleaner to make the data structure a DAG from the start, instead of
tacking DAG-edges to a tree as if they were some afterthought.