Re: [Qemu-devel] [PATCH] initialize unit id of IDE bus

[Gleb Natapov <gleb@redhat.com>]

On Mon, Oct 25, 2010 at 08:06:13PM +0200, Markus Armbruster wrote:
> Gleb Natapov <gleb@redhat.com> writes:
> 
> > 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);
> >> 
> >> 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.
> > Will check tomorrow if this works, but why not have simple property on
> > IDEBus that says which one is it?
> 
> Because nobody has needed it so far?
> 
> Does the bus care whether it's first or second?
> 
User that wants to address particular disk cares.

> >                                   BTW what -device magic should I use to
> > create secondary disk on second IDE bus?
> 
> Try -device ide-drive,bus=ide.1,unit=1,drive=...
Where ide.1 comes from? Why do I need to write ide.1 not just 1. Can I
instantiate ide-device on USB bus by doing -device ide-drive,bus=usb?

--
			Gleb.