Re: [Qemu-devel] [PATCH arm-devs v3 1/9] qom/object: Make uintXX added properties writable

[Michael S. Tsirkin]

On Sun, Dec 15, 2013 at 06:56:48PM +0100, Andreas Färber wrote:
> Am 15.12.2013 06:59, schrieb Peter Crosthwaite:
> > Ping!
> > 
> > I'm trying to figure out what way I want to go here.
> > 
> > On Sat, Dec 7, 2013 at 12:49 AM, Peter Maydell <address@hidden> wrote:
> >> On 3 December 2013 13:19, Andreas Färber <address@hidden> wrote:
> >>> Am 03.12.2013 07:59, schrieb Peter Crosthwaite:
> >>>> Currently the uintXX property adders make a read only property. This
> >>>> is not useful for devices that want to create board (or container)
> >>>> configurable dynamic device properties. Fix by trivially adding property
> >>>> setters to object_property_add_uintXX.
> >>>>
> >>>> Signed-off-by: Peter Crosthwaite <address@hidden>
> >>>> ---
> >>>> changed since v2:
> >>>> msg typo: "trivially"
> >>>
> >>> Not sure if I've asked already, but these functions were added by mst
> >>> (so let's CC him) for accessing read-only constants in ACPI code. Your
> >>> change seems to make them writable - can anything go wrong when the
> >>> setters are used via QMP?
> > 
> > Maybe. But that should be an ACPI problem.
> 
> No, it means that if you change it you need to touch ACPI code as well -
> or to design your change in a way that avoids exactly that, e.g. by
> adding a new API reusing the existing getters rather than changing the
> semantics of the existing API used by ACPI.
> 
> > It seems that the semantics
> > of these qom/object.c APIs has been set by the lead example. Maybe
> > just an extra arg for RD/WR flags would do the trick however?
> 
> If you can get the extra arg passed through as opaque then sure, that
> would be an option, passing false for all existing users.
> 
> >>> I fear we may need two separate sets of
> >>> functions, one read-only, one read-write.
> >>
> >> We don't want a generically writable property for CBAR either, though:
> >> we want the standard qdev property semantics of "writable until
> >> realize, readonly thereafter".
> >>
> > 
> > Well, with a bit of replumbing I spose we could make qdev property
> > adder framework accessible to post_init to have access to
> > setter/getter fns that implement these semantics.
> 
> Sorry, I don't get how that is related to post_init? All that's needed
> is a check of DeviceState::realized in your setter and to error_setg()
> out if true.
> 
> Regards,
> Andreas

I think ability to add read only properties is reasonable though.
ACPI wants these since we calculate the value ourselves.

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