Re: [Xen-devel] [PATCH, RFC]: qemu: hang-free/error-tolerant PCI hot-plug protocol

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Gianni Tedesco writes ("[Xen-devel] [PATCH, RFC]: qemu: 
hang-free/error-tolerant PCI hot-plug protocol"):
> The interface for PCI hotplug is flexible enough to shoot ones-self in
> the foot. It is possible to try to insert a PCI device in to a slot
> already occupied by a qemu emulated device (NIC, PIIX, ISA-bridge, etc.)
> In this case qemu (wisely) refuses to do the hotplug. Since there is no
> way for a toolstack to query qemu's pci device layout there is no way to
> check for this ahead of time. In this case the toolstack must wait for
> device-model state to change to pci-inserted which never happens.

Hrm.

> I propose that when qemu decides not to hot-plug a device that it raise
> the "pci-inserted" status anyway. The tools must then check the
> "parameter" key in xenbus for a non-error string. In other words:

Why do this rather than a new status "pci-insert-failed" ?  How does
this affect existing toolstacks ?

> --- a/hw/piix4acpi.c
> +++ b/hw/piix4acpi.c

I haven't looked at the code near here.  Does qemu log anything ?  If
so then the corresponding toolstack patches should say "consult qemu
logfile".  Otherwise perhaps qemu should.

Ian.

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