[Kimchi-devel] [RFC] Do not block operations due to ref_cnt

Hi, I'd like to propose a change to how Kimchi uses the resource field "ref_cnt". Currently, "ref_cnt" - which stands for "reference count" - is one of the fields returned when looking up a storage volume. Its purpose is to indicate how many times that resource is being used at the moment. For example, if the resource /storagepools/pool/storagevolumes/vol has ref_cnt=1, it means that the disk is attached to 1 VM right now and thus it cannot be attached to another VM. I believe the original idea of this feature is to prevent the same resource from being attached more than once at the same time. However, IMO, that might not always be the desired behavior and there's no way to enforce it completely as those resources can be used outside of Kimchi, where "ref_cnt" doesn't exist. For example, if I have one VM which uses the disk "vol", I'm not able to attach it to another VM via Kimchi; but if I use another libvirt-based VM manager (e.g. virsh), I am able to attach that disk to a different VM. This becomes even trickier when we consider other operations, like snapshots, which can attach/detach disks while they're being reverted to. Also, suppose I might want to inspect one VM's disk from another VM, and then I'd need to attach one disk twice; Kimchi wouldn't allow that by stating that the disk is already in use. I propose Kimchi should stop using "ref_cnt" as a blocking method. The field may still exist for information/warning messages (e.g. "are you sure you want to attach this disk? it's already being used by another VM.") but no operation should be blocked because of it, as it is the case now. As inconsistencies with that value may happen and we have no way to make sure it will always work, we shouldn't annoy the user by stopping them from doing something that may be perfectly valid. Any feedback will be very welcome. Best regards, Crístian.