Re: [libvirt PATCH v2] tools: add virt-qmp-proxy for proxying QMP clients to libvirt QEMU guests

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> 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.

On the other hand, you can configure multiple QMP monitors.

Regardless, users get to do with QMP what users find useful.  No
objections from me.

> 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@redhat.com>