On Tue, Jan 05, 2021 at 05:18:13PM -0300, Daniel Henrique Barboza wrote: > Hi, > > This is something I've been giving a thought after working in Gitlab issue > #72 and decided to run through the ML before hitting the code. > > We don't have an easy way to retrieve the domain that is using an specific > hostdev. Let's say that I want to know which domain is using the PCI card > pci_0000_01_00_2. 'nodedev-dumpxml' will return the hardware/driver capabilities > of the device, such as IOMMU group, driver and so on, but will not inform > which domain is using the hostdev, if any. 'nodedev-list' will simply list > all nodedev names known to Libvirt, without outputting any other information. > > IIUC, the only existing way I can reliably tell whether a hostdev is being > used by domain, aside from having to register the information by myself > during domain definition of course, is via 'virsh dumpxml <domain>' each > existing running domain and matching the nodedev name with the source.address > element of the XML. > > When we consider SR-IOV devices that can have 28+ VFs each (and have lots of > fun caveats, like Github #72 showed us), the capability of hot plug/unplug > hostdevs freely, and lots of running domains, it is clear that we're putting a > considerable pressure in the upper layers (OVirt, or a poor human admin) to > keep track of the nodedevs each running domain is using. An info that we > already have internally and can just expose it. > > I have a few ideas to make this happen: > > 1 - upgrade 'nodedev-list' to add an extra 'assigned to' column > > This is the more straightforward way of exposing the info. A simple 'nodedev-list' > call can retrieve which domain is using which nodedev. To preserve the existing > usage we can add an "--show-assigned-domains" option to control whether we > will display this info. That would mean nodedev-list has to fetch XML for every running guest and parse and extract it. That's not a scalable solution. > 2 - add an '<assigned_to>' element in nodedev XML definition > > I'm not a fan of exposing this in this particular XML because we would mix > host/hw related attributes with domain info. But it would be easier to pull > this off comparing to (1), so I'm mentioning it for the record. This is similar to what we do for the nwfilter-binding and net-port XML where we have an <owner> element present. The complication here is that right now we don't ever touch the nodedev driver when doing host device assignment, and so don't especially want to introduce a dependancy. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
