Re: [libvirt] [PATCH RFC 0/5] Remove usb address set caching

During my work on removing addresses caching, usb addresses were added :). It should be applied on top of: https://www.redhat.com/archives/libvir-list/2016-August/msg00945.html or some small conflicts appear. I took an approach where exactly the same function is used to both calculate and recalculate the address set. It forces us to keep all the usb address handling in such state that reusing that function doesn't perform any changes that aren't needed. It might even be possible to unify the handling of usb devices into one function, "qemuDomainAssignUSBAddresses", and remove some code. For example, virDomainUSBAddressEnsure looks almost exactly like qemuDomainAssignUSBPorts plus virDomainUSBAddressReserve. The end goal would be simply calling qemuDomainAssignUSBAddresses() as many times as we want, for example when creating a new domain or after a hotplug.

To see what I mean, please take a look at qemuDomainAttachUSBMassStorageDevice. If I remove the call to virDomainUSBAddressEnsure and move creating the USB address set somewhere down (after virDomainDiskInsertPreAlloced), it works - the address is assigned flawlessly. Does it make any sense? Is there any reason why we don't add new usb hubs when hotplugging devices?