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Date: Tue, 26 Oct 2010 09:28:43 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] initialize unit id of IDE bus
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To: Markus Armbruster <armbru@redhat.com>
Cc: qemu-devel@nongnu.org

On Mon, Oct 25, 2010 at 06:22:12PM +0200, Markus Armbruster wrote:
> Gleb Natapov <gleb@redhat.com> writes:
> 
> > On Mon, Oct 25, 2010 at 04:29:35PM +0200, Markus Armbruster wrote:
> >> Gleb Natapov <gleb@redhat.com> writes:
> >> 
> >> > Without this patch both buses on PIIX3_IDE device have the same unit id.
> >> 
> >> Are you sure that's wrong?
> >> 
> > So how do I know which bus is it on PIIX3_IDE?
> [...]
> 
> Let me try to explain the IDE pointer thicket.
> 
> piix3-ide provides two IDE buses.  pci_piix_ide_initfn() stores them in
> PCIIDEState member IDEBus bus[2].  Technically redundant, because qdev
> stores child buses in dev.qdev.child_bus.
> 
> IDEBus points back: qbus.parent.
> 
> Up to two IDE devices can sit on each IDE bus.  The first one uses
> IDEBus members master and ifs[0], the second one uses slave and ifs[1].
> 
> ifs[i].bus points back to the IDE bus.
> 
> {master,slave}.qdev.parent_bus point back to the IDE bus.
> 
> Say you got an IDEDevice and want to know which to which of the two
> buses it's connected.  Let's call it d.
> 
> d->qdev.parent_bus is the BusState.
> 
> Upcast to IDEBus: b = DO_UPCAST(IDEBus, qbus, d->qdev.parent_bus).
> 
> b->qbus.parent is the IDE controller.
> 
> Upcast to PCIIDEState: c = DO_UPCAST(PCIIDEState, dev, n->qbus.parent);
> 
This will not work if IDEBus sits on ISA bus. Any other ideas?

> If c->bus[0] == b, it's on the first bus.
> 
> Else it must be on the second bus, i.e. c->bus[1] == b.
> 
> Hope I didn't screw this up too badly.

--
			Gleb.