On Thu, Mar 16, 2017 at 04:17:51PM +0100, Peter Krempa wrote: > On Thu, Mar 16, 2017 at 14:52:47 +0000, Daniel Berrange wrote: >> On Thu, Mar 16, 2017 at 03:50:51PM +0100, Peter Krempa wrote: >>> On Thu, Mar 16, 2017 at 14:42:30 +0000, Daniel Berrange wrote: >>>> On Thu, Mar 16, 2017 at 01:46:38PM +0100, Peter Krempa wrote: >>>>> On Mon, Feb 27, 2017 at 16:41:28 +0100, Francesco Romani wrote: > [...] > >> The scenario where device attach fails is not the problem - you can >> get the same level of reliabilty to that by simply updating the >> global metadata before & after hotplug in the same way. What is >> difficult is when libvirt fails to persist the XML config on disk >> or when libvirt crashes part way through the operation, and other >> akward failure scenarios unrelated to QEMU itself. > In that case you lose the device definition too, since saving the XML is > the integral part of the hotplug operation. Agreed, but that just re-inforces my view that we don't need to provide extra metadata against the device for sake of atomicity. Even the existing hotplug doesn't guarantee any kind of atomicity, so you're not making life worse by performing a separate API call to update the global metadata. Regards, Daniel