Re: [libvirt PATCH] tools: add virt-qmp-proxy for proxying QMP clients to libvirt QEMU guests

On Fri, May 27, 2022 at 10:47:58 +0100, Daniel P. Berrangé wrote: > Libvirt provides QMP passthrough APIs for the QEMU driver and these are > exposed in virsh. It is not especially pleasant, however, using the raw > QMP JSON syntax. QEMU has a tool 'qmp-shell' which can speak QMP and > exposes a human friendly interactive shell. It is not possible to use > this with libvirt managed guest, however, since only one client can > attach to he QMP socket at any point in time. > > The virt-qmp-proxy tool aims to solve this problem. It opens a UNIX > socket and listens for incoming client connections, speaking QMP on > the connected socket. It will forward any QMP commands received onto > the running libvirt QEMU guest, and forward any replies back to the > QMP client. > > $ virsh start demo > $ virt-qmp-proxy demo demo.qmp & > $ qmp-shell demo.qmp > Welcome to the QMP low-level shell! > Connected to QEMU 6.2.0 > > (QEMU) query-kvm > { > "return": { > "enabled": true, > "present": true > } > } > > Note this tool of course has the same risks as the raw libvirt > QMP passthrough. It is safe to run query commands to fetch information > but commands which change the QEMU state risk disrupting libvirt's > management of QEMU, potentially resulting in data loss/corruption in > the worst case. > > Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; > --- > > CC'ing QEMU since this is likely of interest to maintainers and users > who work with QEMU and libvirt > > Note this impl is fairly crude in that it assumes it is receiving > the QMP commands linewise one at a time. None the less it is good > enough to work with qmp-shell already, so I figured it was worth > exposing to the world. It also lacks support for forwarding events > back to the QMP client. I originally wanted to teach the qemu tools to work with libvirt directly similarly how 'scripts/render_block_graph.py' from the qemu tree already does but I guess this is also an option. This is an option too albeit a bit more complex to set up, but on the other hand a bit more universal. I'll have a look at the code a bit later.