Re: [PATCH] hw/ide: Fix crash when plugging a piix3-ide device into the x-remote machine

[Stefan Hajnoczi]

On Tue, Apr 27, 2021 at 07:54:21PM +0200, Philippe Mathieu-Daudé wrote:
> On 4/27/21 7:16 PM, John Snow wrote:
> > On 4/27/21 9:54 AM, Stefan Hajnoczi wrote:
> >> I suggest fixing this at the qdev level. Make piix3-ide have a
> >> sub-device that inherits from ISA_DEVICE so it can only be instantiated
> >> when there's an ISA bus.
> >>
> >> Stefan
> > 
> > My qdev knowledge is shaky. Does this imply that you agree with the
> > direction of Thomas's patch, or do you just mean to disagree with Phil
> > on his preferred course of action?
> 
> My understanding is a disagreement to both, with a 3rd direction :)
> 
> I agree with Stefan direction but I'm not sure (yet) that a sub-device
> is the best (long-term) solution. I guess there is a design issue with
> this device, and would like to understanding it first.
> 
> IIUC Stefan says the piix3-ide is both a PCI and IDE device, but QOM
> only allow a single parent. Multiple QOM inheritance is resolved as
> interfaces, but PCI/IDE qdev aren't interfaces, rather abstract objects.
> So he suggests to embed an IDE device within the PCI piix3-ide device.
> 
> My view is the PIIX is a chipset that share stuffs between components,
> and the IDE bus belongs to the chipset PCI root (or eventually the
> PCI-ISA bridge, function #0). The IDE function would use the IDE bus
> from its root parent as a linked property.
> My problem is currently this device is user-creatable as a Frankenstein
> single PCI function, out of its chipset. I'm not sure yet this is a
> dead end or I could work something out.

Kevin and Paolo previously pointed out that piix3-ide is sometimes used
with the Q35 machine type. The user-creatable piix3-ide device needs to
be deprecated before it can be dropped. That's a long process that
cannot fix the current crash any time soon.

I do support deprecating the user-creatable piix3-ide device in favor of
a proper Q35 Legacy IDE implementation. The main problem is this
involves a bunch of work and I'm not sure who would do it (the payoff is
not very high).

Stefan

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