On 12/01/2011 08:48 AM, Avi Kivity wrote:
On 12/01/2011 04:42 PM, Anthony Liguori wrote:
We need good tools to allow easy review of the ABI bits hiding in
patches, and to maintain ABI compatibility. Something like
qemu-print-abi that dumps all properties for all devices. Patches could
show the ABI changes by including a diff of the output of this program
from before and after a change, and we could add similar tests for
backwards compatibility.
I'm not sure that we want this interface to be backwards compatible.
I actually think we should provide a higher level interface that's
explicitly there for compatibility. Probably in the form of a C
library that can be documented and reasoned with better.
Does this force anyone who wants a stable ABI to use this library?
I don't have a good picture of this library. If FooState has a bar
propery, do you generate qemu_foo_get_bar() and qemu_foo_set_bar()
accessors?
This is all extremely low level stuff. My view is that if you are a user that
cares about backwards compatibility, you probably don't want all of this low
level stuff in the first place.
I think we need to provide two classes of interfaces. A low-level interface
that only something like libvirt would consume that is not 100% backwards
compatible and a higher-level interface that less sophisticated tools would consume.
If we provide a not 100% backwards compatible interface, then we would also need
to provide a good introspection/capabilities mechanism so that something like
libvirt could find out whether a feature was available or whether a device has
changed significantly.
To be very clear, I think "-drive if=virtio" should be absolutely stable
regardless of what we do to the virtio device model. However, I want the
flexibility to remove "-device virtio-blk-pci" and replace it with "-device
virtio-pci,id=foo -device virtio-blk,bus=foo".
We would provide a means to enumerate supported devices so that things like
libvirt could see that virtio-blk-pci is not valid in this new version but now
there is a virtio-pci and virtio-blk device.
Regards,
Anthony Liguori
