Re: [libvirt] [PATCHv2 3/5] S390: QEMU driver support for CCW addresses
On Fri, Feb 08, 2013 at 06:32:22PM +0100, Viktor Mihajlovski wrote:
This commit adds the QEMU driver support for CCW addresses. The
current QEMU only allows virtio devices to be attached to the
CCW bus. We named the new capability indicating that support
QEMU_CAPS_VIRTIO_CCW accordingly.
The fact that CCW devices can only be assigned to domains with a
machine type of s390-ccw-virtio requires a modification in the
capability handling approach.
First, the QEMU binary name alone will not suffice for capability
lookup, we need the machine type as well. For that purpose we
mangle the machine type into the cache lookup key.
The other thing is that the device support probing will
unfortunately always return both the old virtio-*-s390
and the new virtio-*-ccw devices. This makes it impossible to
choose the correct default device address type if the domain
definition XML doesn't contain explict addresses.
Therefore we apply a fix up in the cache lookup: depending
on the machine type we clear either the VIRTIO_S390 or the
VIRTIO_CCW capability.
I'm not a fan of this approach. The capabilities data is reflecting
what the QEMU binary is capable of supporting, *regardless* of what
guest config is chosen.
The decision about whether to use S390 or CCW based on the machine
type value, should be made by the internal method at the point when
it actually assigns addresses, not when we create the capabilities
initially.
Your approach here means we're going to be storing many many more
capabilities instances, and we're going to be re-probing the QEMU
binaries for each machine type. This is absolutely not something
we want todo.
Daniel
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