On 5/27/22 12:20 PM, Peter Krempa wrote:
> 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@xxxxxxxxxx>
>> ---
>>
>> 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.
>
Would have found it useful, at the time I wrote the multifd save series I ended up just scripting around virsh qemu-monitor-command from either bash or C.
One challenge I had to face was, when doing fd migration doing
"execute": "getfd", "arguments": {"fdname":"migrate"}
in that case we have to use the --pass-fds=N option to pass the FD.
Does the virt-qmp-proxy tool consider the passing of FDs issue?
Thanks,
Claudio
