On Tue, 2020-08-18 at 15:15 -0600, Jim Fehlig wrote:
On 8/5/20 2:19 AM, Andrea Bolognani wrote:
I guess we need to start checking the modules directory in addition to the main QEMU binary, and regenerate capabilities every time its contents change.
We recently received reports of this issue on Tumbleweed, which just got the modularized qemu 5.1
https://bugzilla.opensuse.org/show_bug.cgi?id=1175320
Mark, are you working on a patch to invalidate the cache on changes to the qemu modules directory? I suppose it needs to be handled similar to the qemu binaries. E.g. when building the cache include a list of all qemu modules found. When validating the cache see if any modules have disappeared, if any have been added, and if the ctime of any have changed. Yikes, sounds a little more complex than the binaries :-).
I'd like to question whether this effort is justified for an optimization that matters only at libvirtd startup time, and even there saves no more than a few seconds. I propose to simply disable the caching of qemu capabilities (or provide a build-time option to do so). Optimizations that produce wrong results should be avoided.
I wonder if it is possible to use inotify to receive notification of changes to the modules directory?
That would certainly be possible, but it'd be a new feature (getting aware of qemu capability changes during runtime), while we're currently discussing an existing feature (getting qemu capabilities on startup) which is broken. I believe these issues should be discussed separately. Regards, Martin