Re: [libvirt PATCH v3 00/21] Add support for persistent mediated devices

On Mon, Feb 01, 2021 at 10:45:43AM +0100, Erik Skultety wrote: > On Mon, Feb 01, 2021 at 09:42:32AM +0000, Daniel P. Berrangé wrote: > > On Fri, Jan 29, 2021 at 05:34:36PM -0600, Jonathon Jongsma wrote: > > > On Thu, 7 Jan 2021 17:43:54 +0100 > > > Erik Skultety <eskultet(a)redhat.com&gt; wrote: > > > > > > > > Tested with v6.10.0-283-g1948d4e61e. > > > > > > > > > > 1.Can define/start/destroy mdev device successfully; > > > > > > > > > > 2.'virsh nodedev-list' has no '--active' option, which is > > > > > inconsistent with the description in the patch： > > > > > # virsh nodedev-list --active > > > > > error: command 'nodedev-list' doesn't support option --active > > > > > > > > > > 3.virsh client hang when trying to destroy a mdev device which is > > > > > using by a vm, and after that all 'virsh nodev*' cmds will hang. If > > > > > restarting llibvirtd after that, libvirtd will hang. > > > > > > > > It hangs because underneath a write to the 'remove' sysfs attribute > > > > is now blocking for some reason and since we're relying on mdevctl to > > > > do it for us, hence "it hangs". I'm not trying to make an excuse, > > > > it's plain wrong. I'd love to rely on such a basic functionality, but > > > > it looks like we'll have to go with a extremely ugly workaround and > > > > try to get the list of active domains from the nodedev driver and see > > > > whether any of them has the device assigned before we try to destroy > > > > the mdev via the nodedev driver. > > > > > > So, I've been trying to figure out a way to do this, but as far as > > > I know, there's no way to get a list of active domains from within the > > > nodedev driver, and I can't think of any better ways to handle it. Any > > > ideas? > > > > Correct, the nodedev driver isn't permitted to talk to any of the virt > > drivers. > > Oh, not even via secondary connection? What makes nodedev so special, since we > can open a secondary connection from e.g. the storage driver? It is technically possible, but it should never be done, because it introduces a bi-directional dependancy between the daemons which introduces the danger of deadlocking them. None of the secondary drivers should connect to the hypervisor drivers. > > Is there anything in sysfs which reports whether the device is in use ? > > Nothing that I know of, the way it used to work was that you tried to write to > sysfs and kernel returned a write error with "device in use" or something like > that, but that has changed since :(.