[Qemu-devel] Re: Immutable qdev properties

[Gerd Hoffmann <kraxel@redhat.com>]

On 08/24/09 11:05, Markus Armbruster wrote:

> iobase[] will start as whatever the user specifies in -device,
> defaulting to { -1, -1 }, then revert to { 0x441, 0x443 } when the
> device is initialized.  Not sure whether this is a problem.

The ioport properties should reflect the values actually used, even in 
case they can not be configured.  So in case a ISA device finds '-1' aka 
'not specified by the user', it should fill in (and use) the default 
value.  See also below ...

> Taking a step back, the general problem is "immutable" qdev properties,
> i.e. properties that aren't configurable.  I think it would be good to
> agree on a common method there, and document it.

On a even broader view: how to handle invalid property values?

Having a device support one fixed I/O port is just a special case of 
that.  Other ISA devices usually can be configured to a few possible I/O 
bases using dip switches (sound cards for example).  But the possible 
values are usually fairly limited.

In case the user specifies a impossible iobase we can

   (1) ignore it and use defaults instead.
   (2) fix it (pick nearest possible value or so).
   (3) fail.

#3 is probably the most sane, but that depends on the 
init()-callback-can-fail patches ...

cheers,
   Gerd