[ovirt-devel] [vdsm] Infrastructure design for node (host) devices

Hello, I'm actively working on getting host device passthrough (pci, usb and scsi) exposed in VDSM, but I've encountered growing complexity of this feature. The devices are currently created in the same manner as virtual devices and their reporting is done via hostDevices list in getCaps. As I implemented usb and scsi devices, the size of this list grew almost twice - and that is on a laptop. Similar problem is with the devices themselves, they are closely tied to host and currently, engine would have to keep their mapping to VMs, reattach back loose devices and handle all of this in case of migration. I would like to hear your opinion on building something like host device pool in VDSM. The pool would be populated and periodically updated (to handle hot(un)plugs) and VMs/engine could query it for free/assigned/possibly problematic devices (which could be reattached by the pool). This has added benefit of requiring fewer libvirt calls, but a bit more complexity and possibly one thread. The persistence of the pool on VDSM restart could be kept in config or constructed from XML. I'd need new API verbs to allow engine to communicate with the pool, possibly leaving caps as they are and engine could detect the presence of newer vdsm by presence of these API verbs. The vmCreate call would remain almost the same, only with the addition of new device for VMs (where the detach and tracking routine would be communicated with the pool).