On 01/20/2011 03:33 AM, Jan Kiszka wrote:
On 2011-01-19 20:32, Blue Swirl wrote:
On Wed, Jan 19, 2011 at 4:57 PM, Anthony Liguori
<aliguori@xxxxxxxxxxxxxxxxxx> wrote:
On 01/19/2011 07:15 AM, Markus Armbruster wrote:
So they interact with KVM (need kvm_state), and they interact with the
emulated PCI bus. Could you elaborate on the fundamental difference
between the two interactions that makes you choose the (hypothetical)
KVM bus over the PCI bus as device parent?
It's almost arbitrary, but I would say it's the direction that I/Os flow.
But if the underlying observation is that the device tree is not really a
tree, you're 100% correct. This is part of why a factory interface that
just takes a parent bus is too simplistic.
I think we ought to introduce a -pci-device option that is specifically for
creating PCI devices that doesn't require a parent bus argument but provides
a way to specify stable addressing (for instancing, using a linear index).
I think kvm_state should not be a property of any device or bus. It
should be split to more logical pieces.
Some parts of it could remain in CPUState, because they are associated
with a VCPU.
Also, for example irqfd could be considered to be similar object to
char or block devices provided by QEMU to devices. Would it make sense
to introduce new host types for passing parts of kvm_state to devices?
I'd also make coalesced MMIO stuff part of memory object. We are not
passing any state references when using cpu_physical_memory_rw(), but
that could be changed.
There are currently no VCPU-specific bits remaining in kvm_state. It may
be a good idea to introduce an arch-specific kvm_state and move related
bits over. It may also once be feasible to carve out memory management
related fields if we have proper abstractions for that, but I'm not
completely sure here.
Anyway, all these things are secondary. The primary topic here is how to
deal with kvm_state and its fields that have VM-global scope.
The debate is really:
1) should we remove all passing of kvm_state and just assume it's static
2) deal with a couple places in the code where we need to figure out how
to get at kvm_state
I think we've only identified 1 real instance of (2) and it's resulted
in some good discussions about how to model KVM devices vs. emulated
devices. Honestly, (1) just stinks. I see absolutely no advantage to
it at all. In the very worst case scenario, the thing we need to do is
just reference an extern variable in a few places. That completely
avoids all of the modelling discussions for now (while leaving for
placeholder FIXMEs so the problem can be tackled later).
I don't understand the resistance here.
Regards,
Anthony Liguori
Jan
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