Re: [libvirt] [PATCH 3/3] qemu_process: add check for hyperv features

30.03.2016 10:50, Pavel Hrdina пишет: > On Tue, Mar 29, 2016 at 07:06:14PM +0300, Maxim Nestratov wrote: >> 29.03.2016 16:31, Pavel Hrdina пишет: >>> Commit 7068b56c introduced several hyperv features. Not all hyperv >>> features are supported by old enough kernels and we shouldn't allow to >>> start a guest if kernel doesn't support any of the hyperv feature. >>> >>> There is one exception, for backward compatibility we cannot error out >>> if one of the RELAXED, VAPIC or SPINLOCKS isn't supported, for the same >>> reason we ignore invtsc, to not break restoring saved domains with older >>> libvirt. >>> > [...] > >> Hmm, qemu already checks them and simply ignores most of them and >> doesn't prevent guest from starting in case they are not supported and >> optional. In case they are reqired it fails. Why should we check them >> here? At least we should follow the logic qemu has. > Yes, that's true that QEMU do some checks and ignores most of the features > missing in kernel, but that's no reason why we should do the same. Libvirt > tries to present in domain XML only those features and devices that are actually > present in the guest. Thus if you tell libvirt that you want some hyperv > feature but your host kernel doesn't support it, we should let the user know > that this feature isn't supported instead of ignoring that fact and start the > guest anyway. > > Pavel I see your point. And what if a user wants to define some features just to ask libvirt/qemu to do its best if possible and ignore if it isn't without redefining domain xml? Does such case make sense? Maxim