Re: [Qemu-devel] [PATCH RFC V2 0/9] qemu-machine as a QOM object

[Paolo Bonzini]

Il 03/03/2014 13:07, Marcel Apfelbaum ha scritto:
> > Another early refactoring should be to pass &current_machine->init_args
> > to machine->init, not the "args".
> Problem is that this is a "private field", should I add a getter for it?

vl.c is already accessing it one line before, isn't it?

So vl.c is already looking at QemuMachineState internals.  I expected 
this to be temporary.

> > Now here's a possible plan to get rid of QEMUMachineInitArgs:
> >
> > 1) Add three wrappers to QemuMachine for reading kernel_filename,
> > kernel_cmdline, initrd_filename.  Unlike object_property_get_str, they
> > can skip the strdup of the value.  This way you don't have to add the
> > matching free to all uses of the fields.
>
> I have nothing against it, but this will break QEMU's unified way to
> handle object properties, right?
> Meaning I will have a field  of the object state(kernel_filename)
> and I will add a method like machine_get_field(QemuMachineState) going
> "around" QOM,,,

True.  On the other hand, I believe there is a purpose in using getters 
and setters: using object_property_get/set all the time is more verbose 
and especially less type-safe.  I prefer adding getters to naming 
properties with #define.  Especially if you need getters but not setters.

GObject uses a similar scheme where you have both regular 
getters/setters and properties.  Static languages use the getters and 
setters, while bindings for dynamic languages will always go through 
properties.

> > 2) Similarly, add get/set functions (not properties, since these are not
> > accessible via -machine) for ram_size, boot_order, cpu_model.
>
> I am sorry, here you lost me, what do you mean "accessible via -machine"?
> Maybe that cannot be queried by QOM tree?

Not yet, at least.  I prefer to keep these fields out of QOM because 
they cannot be set with -machine.  cpu_model is already accessible since 
it's related to the class of the CPU devices.

> Those getter/setters are not the same wrappers as above, going around "QOM"?

Actually they are the same thing.  But I think above you only need 
getters.  Here you also need setters.

> > 3) Now you can have something like patch 8 in this series.
> I also need patch 5 that deals with getting a string property with NULL value,

Ok.

> I see no reason why not, the main problem I see is the use of those wrappers
> or setters/getters, I suspect that the usage will be:
> 1. global QOM query to get the machine
> 2. Use this wrappers(getters/setters) to do query/alter the machine.

I think setters should appear only in vl.c.

> Doesn't QOM have another way to do this? Or I am missing something, of course.

I don't know really.  My main requirement is not to change the -machine 
interface.

Paolo