Re: [Qemu-devel] [PATCH RFC 0/3] qdev: order devices by priority before creating them

[Michael S. Tsirkin]

On Tue, May 10, 2016 at 10:28:43AM +0200, Markus Armbruster wrote:
> Marcel Apfelbaum <address@hidden> writes:
> 
> > This series aims to allow more devices to be used with '-device'
> > by sorting the devices based on a predefined creation order flag
> > before creating them.
> >
> > Devices like IOMMU need to be created before others, so they can leverage
> > the DeviceCreationPriority flag introduced by the first patch to 
> > DeviceClass.
> >
> > The second patch sorts the devices by their DeviceCreationPriority
> > before creating them.
> >
> > Finally, the last patch demonstrates how it can be used to ensure
> > the creation of host-bridges before the pci-bridges and pci-bridges before
> > the others.
> >
> > I preferred to combine all the priorities into a single enum
> > to better manage the creation order.
> >
> > This is an RFC because I only wanted to know if it seems like the right way 
> > to go.
> > Comments are appreciated,
> 
> Can you explain why requiring the user to specify -device in a sane
> order isn't good enough?

Because it requires knowledge about the hardware.
For example, how do users know that iommu must come before the devices?
They don't. They often don't know their devices are pci devices even.

-- 
MST