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[Qemu-devel] Re: Immutable qdev properties

From: Gerd Hoffmann
Subject: [Qemu-devel] Re: Immutable qdev properties
Date: Mon, 24 Aug 2009 14:25:29 +0200
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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 ...


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