[libvirt PATCH v3] tools: add virt-qemu-qmp-proxy for proxying QMP via libvirt QEMU guests

[Daniel P. Berrangé]

On Fri, Oct 07, 2022 at 03:22:33PM +0200, Michal Prívozník wrote:
> On 10/5/22 12:51, 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 the QMP socket at any point in time. While it would be
> > possible to configure a second QMP socket for a VM, it may not be
> > an known requirement at the time the guest is provisioned.
> > 
> > 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. It will also forward back events.
> > 
> >   $ 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. Any use of this tool will cause the guest to be marked
> > as tainted as an warning that it could be in an unexpected state.
> > 
> > Since this tool introduces a python dependency it is not desirable
> > to include it in any of the existing RPMs in libvirt. This tool is
> > also QEMU specific, so isn't appropriate to bundle with the generic
> > tools. Thus a new RPM is introduced 'libvirt-clients-qemu', to
> > contain additional QEMU specific tools, with extra external deps.
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> > ---
> > 
> > In v3:
> > 
> >   - Added to libvirt-clients-qemu RPM
> >   - Renamed to virt-qemu-qmp-proxy
> > 
> >  docs/manpages/meson.build             |   1 +
> >  docs/manpages/virt-qemu-qmp-proxy.rst | 120 +++++++++
> >  libvirt.spec.in                       |  15 ++
> >  tools/meson.build                     |   5 +
> >  tools/virt-qemu-qmp-proxy             | 360 ++++++++++++++++++++++++++
> >  5 files changed, 501 insertions(+)
> >  create mode 100644 docs/manpages/virt-qemu-qmp-proxy.rst
> >  create mode 100755 tools/virt-qemu-qmp-proxy
> > 
> 
> > diff --git a/tools/virt-qemu-qmp-proxy b/tools/virt-qemu-qmp-proxy
> > new file mode 100755
> > index 0000000000..d85342bd2b
> > --- /dev/null
> > +++ b/tools/virt-qemu-qmp-proxy
> 
> > +    @staticmethod
> > +    def make_file(fd):
> > +        flags = fcntl.fcntl(fd, fcntl.F_GETFL)
> > +
> > +        mask = os.O_RDONLY | os.O_WRONLY | os.O_RDWR | os.O_APPEND
> > +        flags = flags & mask
> > +        mode = ""
> > +        if flags == os.O_RDONLY:
> > +            mode = "rb"
> > +        elif flags == os.O_WRONLY:
> > +            mode = "wb"
> > +        elif flags == os.O_RDWR:
> > +            mode = "r+b"
> > +        elif flags == (os.O_WRONLY | os.O_APPEND):
> > +            mode = "ab"
> > +        elif flags == (os.O_RDWR | os.O_APPEND):
> > +            mode = "a+b"
> > +
> > +        return os.fdopen(fd, mode)
> 
> 
> This upsets syntax-check. Squash this in:

For that matter 'flake8' hates my whitespace, so I'll fix that too

> (or add .py suffix, but I dislike that actually).

Yeah, likewise

> Reviewed-by: Michal Privoznik <mprivozn at redhat.com>


With regards,
Daniel
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