Re: [libvirt] [PATCH v2] qemu: Introduce caching whether /dev/kvm is accessible

On Thu, Nov 01, 2018 at 09:31:50AM +0100, Martin Kletzander wrote: > On Tue, Oct 30, 2018 at 03:07:59PM +0000, Daniel P. Berrangé wrote: > > On Tue, Oct 30, 2018 at 03:45:36PM +0100, Michal Privoznik wrote: > > > On 10/30/2018 02:46 PM, Michal Privoznik wrote: > > > > > > > > It is kernel problem. In my testing, the moment I call: > > > > > > > > ioctl(kvm, KVM_CREATE_VM, 0); > > > > > > Okay, I have to retract this claim. 'udevadm monitor' shows some events: > > > > > > KERNEL[3631.129645] change /devices/virtual/misc/kvm (misc) > > > UDEV [3631.130816] change /devices/virtual/misc/kvm (misc) > > > > > > and stopping udevd leaves all three times untouched. So it is udev after > > > all. I just don't know how to find the rule that is causing the issue. > > > Anyway, as for this patch, I think we can merge it in the end, can't we? > > > > Not really. Udev is in use everywhere, so this behaviour makes the > > patch useless in practice, even though it is technically right in > > theory :-( > > > > Does it? With this behaviour we still do the "expensive" work after any machine > has started. But for one machine starting it still has the effect of running it > only once. And we *need* to run it for each machine unless we also cache the > result per (at least) user:group of that machine as every machine can run under > different user:group. Yes, with the current patch it still rechecks it for each VM startup

, but I was going to suggest the caching of this is simply put in a global static variable as there's no reason to record this device permissions state in the per VM caps cache.

Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|