On Thu, Jun 22, 2017 at 09:28:57AM -0600, Alex Williamson wrote:
On Thu, 22 Jun 2017 17:14:48 +0200 Erik Skultety <eskultet@redhat.com> wrote:
[...]
^this is the thing we constantly keep discussing as everyone has a slightly different angle of view - libvirt does not implement any kind of policy, therefore the only "configuration" would be the PCI parent placement - you say what to do and we do it, no logic in it, that's it. Now, I don't understand taking care of the guesswork for the user in the simplest manner possible as policy rather as a mere convenience, be it just for developers and testers, but even that might apparently be perceived as a policy and therefore unacceptable.
I still stand by idea of having auto-creation as unfortunately, I sort of still fail to understand what the negative implications of having it are - is that it would get just unnecessarily too complex to maintain in the future that we would regret it or that we'd get a huge amount of follow-up requests for extending the feature or is it just that simply the interpretation of auto-create == policy?
The increasing complexity of the qemu driver is a significant concern with adding policy based logic to the code. THinking about this though, if we provide the inactive node device feature, then we can avoid essentially all new code and complexity QEMU driver, and still support auto-create.
ie, in the domain XML we just continue to have the exact same XML that we already have today for mdevs, but with a single new attribute autocreate=yes|no
<devices> <hostdev mode='subsystem' type='mdev' model='vfio-pci' autocreate="yes"> <source> <address uuid='c2177883-f1bb-47f0-914d-32a22e3a8804'>
So, just for clarification of the concept, the device with ^this UUID will have had to be defined by the nodedev API by the time we start to edit the domain XML in this manner in which case the only thing the autocreate=yes would do is to actually create the mdev according to the nodedev config, right? Continuing with that thought, if UUID doesn't refer to any of the inactive configs it will be an error I suppose? What about the fact that only one vgpu type can live on the GPU? even if you can successfully identify a device using the UUID in this way, you'll still face the problem, that other types might be currently occupying the GPU and need to be torn down first, will this be automated as well in what you suggest? I assume not.
</source> </hostdev> </devices>
In the QEMU driver, then the only change required is
if (def->autocreate) virNodeDeviceCreate(dev)
Aha, so if a device gets torn down on shutdown, we won't face the problem with some other devices being active, all of them will have to be in the inactive state because they got torn down during the last shutdown - that would work.
I'm not familiar with how inactive devices would be defined in the nodedev API, would someone mind explaining or providing an example please? I don't understand where the metadata is stored that describes the what and where of a given UUID. Thanks,
It would basically copy what we do for domains. Currently there is virNodeDeviceCreateXML() which takes the XML definitions and creates a new active node device and virNodeDeviceDestroy() which takes as argument an object of existing active node device. We would extend the functionality with new APIs: - virNodeDeviceCreate() which would take as argument an object of existing inactive node device. - virNodeDeviceDefineXML() would define the node device as inactive. With the virNodeDeviceDefineXML() you would create a list of predefined inactive devices which could be obtained by virConnectListAllNodeDevices() for example. Internally we would store XML files the same way as we do for domains, somewhere in "/etc/libvirt/..." and like with domains the APIs would work with these files. In virsh terms there would be similar analogy to the domain commands: "virsh nodedev-start" could simply map to virNodeDeviceCreate() and would work like "virsh start" for domains and "virsh nodedev-define" woudl map to virNodeDeviceDefineXML() and work the same way as "virsh define". You could simply list the predefined mdev devices using "virsh nodedev-list", get UUID of existing mdev device and use it in a domain. In virt-manager there could be new type of hostdev device where you could select on of existing mdev devices from a drop-down list where virt-manager would show nice user-friendly descriptions of the mdev devices but under the hood it would put the UUID in the domain XML. Pavel
Alex
-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list