Re: [libvirt] [PATCH RFC 0/3] Add mechanisms to force QEMU capabilities refetches

Sending as an RFC primarily because I'm looking for whether either or both mechanisms in the series is more or less desired. Likewise, if it's felt that the current process of telling customers to just delete the cache is acceptible, then so be it. If there's other ideas I'm willing to give them a go too. I did consider adding a virsh option to "virsh capabilities" (still possible) and/or a virt-admin option to force the refresh. These just were "easier" and didn't require an API adjustment to implement. Patch1 is essentially a means to determine if the kernel config was changed to allow nested virtualization and to force a refresh of the capabilities in that case. Without doing so the CPU settings for a guest may not add the vmx=on depending on configuration and for the user that doesn't make sense. There is a private bz on this so I won't bother posting it. Patch2 and Patch3 make use of the 'service libvirtd reload' function in order to invalidate all the entries in the internal QEMU capabilities hash table and then to force a reread. This perhaps has downsides related to guest usage and previous means to use reload and not refresh if a guest was running. On the other hand, we tell people to just clear the QEMU capabilities cache (e.g. rm /var/cache/libvirt/qemu/capabilities/*.xml) and restart libvirtd, so in essence, the same result. It's not clear how frequently this is used (it's essentially a SIGHUP to libvirtd).