On Wed, Oct 04, 2017 at 08:31:36AM +0200, Martin Kletzander wrote: > On Tue, Oct 03, 2017 at 03:10:48PM +0100, Daniel P. Berrange wrote: > > On Tue, Oct 03, 2017 at 04:03:20PM +0200, Martin Kletzander wrote: > > > On Tue, Oct 03, 2017 at 02:53:46PM +0100, Daniel P. Berrange wrote: > > > > On Tue, Oct 03, 2017 at 02:11:44PM +0200, Martin Kletzander wrote: > > > > > On Tue, Oct 03, 2017 at 12:58:59PM +0200, Michal Privoznik wrote: > > > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1434451 > > > > > > > > > > > > It comes handy for management application to be able to have a > > > > > > per-device label so that it can uniquely identify devices it > > > > > > cares about. The advantage of this approach is that we don't have > > > > > > to generate aliases at define time (non trivial amount of work > > > > > > and problems). The only thing we do is parse the user supplied > > > > > > UUID and format it back. For instance: > > > > > > > > > > > > <disk type='block' device='disk'> > > > > > > <driver name='qemu' type='raw'/> > > > > > > <source dev='/dev/HostVG/QEMUGuest1'/> > > > > > > <target dev='hda' bus='ide'/> > > > > > > <uuid>1efaf08b-9317-4b0f-b227-912e4bd9f483</uuid> > > > > > > <address type='drive' controller='0' bus='0' target='0' unit='0'/> > > > > > > </disk> > > > > > > > > > > > > Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> > > > > > > --- > > > > > > > > > > > > This is just a very basic implementation. If I get a green light on this, I can > > > > > > implement the feature further, i.e. allow device lookup on the UUID. For > > > > > > instance: > > > > > > > > > > > > virsh domiftune fedora $UUID $bandwidth > > > > > > > > <snip> > > > > > > > > I'm thinking that part of the problem we're having with agreeing how to > > > > deal with this RFE is that we're over-analysing semantics, by wondering > > > > whether its a unique name or UUID, its relation to alias, whether it has > > > > bearing on APIs. > > > > > > > > How about we change tack, and do what we did when we needed application > > > > specific information at the top level - just declare a general purpose > > > > <metadata> element and say it is a completely opaque blob. Libvirt will > > > > *never* do anything with it, other than to preserve it exactly as is. > > > > No API will ever use the metadata in any way. Libvirt will never try to > > > > guarantee uniqueness of metadata for each device. It can be JSON or a > > > > gziped microsoft word document for all we care. Entirely upto the app > > > > developer to decide what metadata is saved and guarantee uniqueness if > > > > they so desired. > > > > > > > > > > That is kind of what I was aiming for. But in order for it to be cleaner and > > > easier to use from user as well (and not only mgmt apps) I thought the metadata > > > would just be one identifier. If you want to store more metadata for the > > > device, then you can do all that in the domain metadata and just reference the > > > particular device using the identifier if mgmt app wants to do that. > > > > Yes that is certainly possible. The caveats are that we still need a unique > > identifier for the device, and the metadata update is not atomic wrt > > to device hotplug. > > > > Yes, well, our (libvirt) unique identifier is not going anywhere, so > that's OK, we'll be using what we have been until now. > > > The plus side of the global metadata is that we have APIs to update it > > on the fly already, and its fully namespaced to allow multiple independant > > data sets to be stored. > > > > Yes, exactly. > > > I don't think lack of atomicity is a big deal as you could order it so that > > you update metadata before doing the hotplug. Then worst case you have a > > device mentioned in metadata that doesn't exist, which is easy enough to > > detect. > > > > Right, if you want metadata for device, then you'll just update > metadata, hotplug device, and if it failed you update the metadata once > more. > > So are we on the same page? By that I mean agreeing on any sane user-supplied > identifier that we'll not guarantee uniqueness for, and neither will we use it > for anything for now? (We can deal with the issues regarding using it when > someone wants to actually implement it). Per my reply to the earlier patch series, I'm now inclined to say that we should - Allow the mgmt app to set the aliases upfront - Auto-fill missing aliases at XML define time it has some downsides, but all the other solutions we've discussed have their own downsides too. So on balance I think its not worth it to add a second identifier for each device, when we already have alias. 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 :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
