Re: [libvirt] Fwd: In Use tracker for network and pci-passthrough devices: Laine response

> In the meantime, I think the right way to do this is by integrating with > the code in the qemu driver that keeps track of which PCI devices are in > use. This already happens at the very basic level of "if the device > allocated by the network driver is in use, the attempt to assign the > device will fail"; instead, the network driver should be able to ask > qemu if the device it wants to allocate to the guest is already in use > (and reserve it, in one atomic operation). > > Of course, once the network driver has reserved the device from qemu's > PCI passthrough code, it would return that device to the qemu driver > code that wants to attach the interface, and it would fail because it > would be told the device is already in use (well, yeah! *We* just marked > it as in-use!). To make that work, I guess some sort of > cookie/handle/pointer would need to be passed from qemu's pci > passthrough code back to the network driver, and the network driver > would return it back to qemu's network interface attach code, which > would then use that special cookie/handle/pointer to attach the device > (saying "yeah, I know it's already in use, and here's my pass-card"). Wouldn't this approach require network driver to call functions from the qemu driver? I think this is not good for the hierarchical structure we are trying to maintain.

> > (Talking about this makes me think that the code that keeps track of PCI > device allocation shouldn't really be a part of qemu, but should be a > separate module, so that the network driver can still function properly > even if the qemu driver isn't loaded.) Would this mean moving code to a new driver called device_driver.c or devicetracker_driver.c (which consumes device_conf.ch) and is called by network, domain and qemu drivers?