On Thu 14 Jun 2018 11:00:55 AM CEST, Kevin Wolf <kw...@redhat.com> wrote: > Am 13.06.2018 um 18:41 hat Max Reitz geschrieben: >> On 2018-06-13 18:02, Eric Blake wrote: >> > On 06/13/2018 10:47 AM, Denis Plotnikov wrote: >> >> The command enables/disables copy-on-read mode for VM's disk while >> >> VM is running. >> >> >> >> This is needed when using external disk readers to shape access pattern >> >> to the disk backend. >> >> >> >> Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> >> >> --- >> > >> > Deferring thoughts on the actual design for later; >> >> But why? ;-) >> >> This patch would definitely be superseded by a block reconfiguration >> command (i.e. presumably one that makes reopen accessible over QMP). >> With such a command, you could insert or remove a copy-on-read filter >> node at any point in time. >> >> Since we definitely want block graph configuration, I don't think we >> want to add special commands now. > > I agree, and it seems that we get more and more use cases for a block > reconfiguration commands. Only yesterday we talked about the "true" > blockdev way for libvirt to implement I/O throttling. The result was > that without reopen, we still need to use the old QMP command to set > BlockBackend-based I/O throttling instead of using a filter node. > > So I'm eagerly awaiting Berto's promised patches for it.
They're coming, it's just a bit tricker than I initially though. I'll probably send the first series as an RFC if I don't manage to fix all problems, so we can discuss them a bit. Berto
