Dor Laor wrote: > Anthony Liguori wrote: >> Dor Laor wrote: >>>> >>> In general I think we need to add another feature or even version >>> number ( I know you guys hate it). >>> The reason is - Let's say you dont change functionality but change >>> the irq protocol (for example the isr won't be zeroed on read), then >>> an old >>> guest driver wouldn't know it runs on a new host version and will >>> have its irq line pulled up. >>> So I suggest adding a capability of VIRTIO_ISR_CLEAR_XXX or adding a >>> version number. >>> Comments? >> >> I don't think we'll actually change the ISR protocol. I think it's >> the best that it can actually be. However, if we do need to change >> the ABI for some reason, I think the right thing to do is just use a >> new device ID (since it's effectively a new device). >> >> Regards, >> >> Anthony Liguori > Changing the devid is acceptable and much more easier then backward > compatibility support, I prefer it too. > Note that there are some disadvantages when changing the devid - For > example, > if you installed an old device drivers in the guest kernel and after a > while you bring the guest down, > upgrade the kvm host version and bring the guest back up. > If it has a new device id (and since the abi is not maintained the > driver won't match VENDOR=virtio; DEVID=*), > then the guest won't have a driver for the new device. > In that case I think a guest agent can switch to fully virtualized > device and afterwards install the driver automatically. > This is what we do in our production environment.
Hrm, I have to think about backwards compatibility at the virtio-pci layer. virtio-pci basically exposes two things, the first is an ABI for doing bidirectional notification and setting driver status. The second is a standard and transparent mechanism for virt_rings. I think that the first is simply enough that we don't need a feature mask or a version number. Maybe perhaps with the status bits, I don't know. For the virt_rings, if we had something more sophisticated than virt_rings down the road, that can be discovered/configured in the per-device configuration area so I don't think we need feature/version info for that. Rusty, Avi: any thoughts? I'm a bit on the fence. Regards, Anthony Liguori > Regards, > Dor ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
