On 6/20/22 19:19, 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@redhat.com> ---
Changed in v2:
- Rewrote to not be such a gross hack, specifically - Wired up usage of libvirt event loop for sock I/O - Register with libvirt for QMP events - Incrementally read from socket & try json parsing until we get a full command, instead of assuming a full command in one read - Forwarding of passed FDs in both directions (libvirt -> client untested, since AFAIK, no QMP cmd returns FDs currently)
Other thought....
This patch is against libvirt.git but has a dependancy on the libvirt-python.git APIs. If we put this in libvirt-client RPM then we get a new dep on python.
Perhaps better to have this live in libvirt-python.git/examples, though I would like it present as a standard tool ? Another option is to bundle with virt-install which is a python app commonly present on virt hosts ?
Or, we could have it in a separate RPM which would require libvirt-client and libvirt-python.
docs/manpages/meson.build | 1 + docs/manpages/virt-qmp-proxy.rst | 120 +++++++++++ tools/meson.build | 5 + tools/virt-qmp-proxy | 360 +++++++++++++++++++++++++++++++ 4 files changed, 486 insertions(+) create mode 100644 docs/manpages/virt-qmp-proxy.rst create mode 100755 tools/virt-qmp-proxy
Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Michal