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

[Michal Prívozník]

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:

diff --git i/build-aux/syntax-check.mk w/build-aux/syntax-check.mk
index 649eb91acb..e35c2be734 100644
--- i/build-aux/syntax-check.mk
+++ w/build-aux/syntax-check.mk
@@ -1363,7 +1363,7 @@ exclude_file_name_regexp--sc_prohibit_strdup = \
   ^(docs/|examples/|tests/virnetserverclientmock.c|tests/commandhelper.c|tools/nss/libvirt_nss_(leases|macs)\.c$$)
 
 exclude_file_name_regexp--sc_prohibit_close = \
-  (\.p[yl]$$|\.spec\.in$$|^docs/|^(src/util/vir(file|event)\.c|src/libvirt-stream\.c|tests/(vir.+mock\.c|commandhelper\.c|qemusecuritymock\.c)|tools/nss/libvirt_nss_(leases|macs)\.c)$$)
+  (\.p[yl]$$|\.spec\.in$$|^docs/|^(src/util/vir(file|event)\.c|src/libvirt-stream\.c|tests/(vir.+mock\.c|commandhelper\.c|qemusecuritymock\.c)|tools/nss/libvirt_nss_(leases|macs)\.c)|tools/virt-qemu-qmp-proxy$$)
 
 exclude_file_name_regexp--sc_prohibit_empty_lines_at_EOF = \
   (^tests/(nodedevmdevctl|virhostcpu|virpcitest|virstoragetest)data/|docs/js/.*\.js|docs/fonts/.*\.woff|\.diff|tests/virconfdata/no-newline\.conf$$)

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

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

Michal