[libvirt PATCH] tools: add virt-qmp-proxy for proxying QMP clients to libvirt QEMU guests
Daniel P. Berrangé
berrange at redhat.com
Fri May 27 09:47:58 UTC 2022
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 at redhat.com>
---
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.
docs/manpages/meson.build | 1 +
docs/manpages/virt-qmp-proxy.rst | 123 ++++++++++++++++++++++++++++
tools/meson.build | 5 ++
tools/virt-qmp-proxy | 133 +++++++++++++++++++++++++++++++
4 files changed, 262 insertions(+)
create mode 100644 docs/manpages/virt-qmp-proxy.rst
create mode 100755 tools/virt-qmp-proxy
diff --git a/docs/manpages/meson.build b/docs/manpages/meson.build
index ba673cf472..4162a9969a 100644
--- a/docs/manpages/meson.build
+++ b/docs/manpages/meson.build
@@ -18,6 +18,7 @@ docs_man_files = [
{ 'name': 'virt-pki-query-dn', 'section': '1', 'install': true },
{ 'name': 'virt-pki-validate', 'section': '1', 'install': true },
{ 'name': 'virt-qemu-run', 'section': '1', 'install': conf.has('WITH_QEMU') },
+ { 'name': 'virt-qmp-proxy', 'section': '1', 'install': conf.has('WITH_QEMU') },
{ 'name': 'virt-xml-validate', 'section': '1', 'install': true },
{ 'name': 'libvirt-guests', 'section': '8', 'install': conf.has('WITH_LIBVIRTD') },
diff --git a/docs/manpages/virt-qmp-proxy.rst b/docs/manpages/virt-qmp-proxy.rst
new file mode 100644
index 0000000000..94679406ab
--- /dev/null
+++ b/docs/manpages/virt-qmp-proxy.rst
@@ -0,0 +1,123 @@
+==============
+virt-qmp-proxy
+==============
+
+--------------------------------------------------
+Expose a QMP proxy server for a libvirt QEMU guest
+--------------------------------------------------
+
+:Manual section: 1
+:Manual group: Virtualization Support
+
+.. contents::
+
+
+SYNOPSIS
+========
+
+``virt-qmp-proxy`` [*OPTION*]... *DOMAIN* *QMP-SOCKET-PATH*
+
+
+DESCRIPTION
+===========
+
+This tool provides a way to expose a QMP proxy server that communicates
+with a QEMU guest managed by libvirt. This enables standard QMP client
+tools to interact with libvirt managed guests.
+
+**NOTE: use of this tool will result in the running QEMU guest being
+marked as tainted.** It is strongly recommended that this tool *only be
+used to send commands which query information* about the running guest.
+If this tool is used to make changes to the state of the guest, this
+may have negative interactions with the QEMU driver, resulting in an
+inability to manage the guest operation thereafter, and in the worst
+case **potentially lead to data loss or corruption**.
+
+The ``virt-qmp-proxy`` program will listen on a UNIX socket for incoming
+client connections, and run the QMP protocol over the connection. Any
+commands received will be sent to the running libvirt guest, and replies
+sent back.
+
+The ``virt-qemu-proxy`` program may be interrupted (eg Ctrl-C) when it
+is no longer required. The libvirt QEMU guest will continue running.
+
+
+OPTIONS
+=======
+
+*DOMAIN*
+
+The ID or UUID or Name of the libvirt QEMU guest.
+
+*QMP-SOCKET-PATH*
+
+The filesystem path at which to run the QMP server, listening for
+incoming connections.
+
+``-c`` *CONNECTION-URI*
+``--connect``\ =\ *CONNECTION-URI*
+
+The URI for the connection to the libvirt QEMU driver. If omitted,
+a URI will be auto-detected.
+
+``-v``, ``--verbose``
+
+Run in verbose mode, printing all QMP commands and replies that
+are handled.
+
+``-h``, ``--help``
+
+Display the command line help.
+
+
+EXIT STATUS
+===========
+
+Upon successful shutdown, an exit status of 0 will be set. Upon
+failure a non-zero status will be set.
+
+
+AUTHOR
+======
+
+Daniel P. Berrangé
+
+
+BUGS
+====
+
+Please report all bugs you discover. This should be done via either:
+
+#. the mailing list
+
+ `https://libvirt.org/contact.html <https://libvirt.org/contact.html>`_
+
+#. the bug tracker
+
+ `https://libvirt.org/bugs.html <https://libvirt.org/bugs.html>`_
+
+Alternatively, you may report bugs to your software distributor / vendor.
+
+NOTE: at this time there is no support for forwarding QMP events back
+to the clients
+
+COPYRIGHT
+=========
+
+Copyright (C) 2022 by Red Hat, Inc.
+
+
+LICENSE
+=======
+
+``virt-qemu-proxy`` is distributed under the terms of the GNU LGPL v2+.
+This is free software; see the source for copying conditions. There
+is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE
+
+
+SEE ALSO
+========
+
+virsh(1), `https://libvirt.org/ <https://libvirt.org/>`_,
+`QMP reference <https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html>`_
diff --git a/tools/meson.build b/tools/meson.build
index bb28a904dc..4e959ecf0b 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -320,6 +320,11 @@ if conf.has('WITH_LIBVIRTD')
endif
endif
+if conf.has('WITH_QEMU')
+ install_data('virt-qmp-proxy',
+ install_dir: bindir)
+endif
+
if bash_completion_dep.found()
subdir('bash-completion')
endif
diff --git a/tools/virt-qmp-proxy b/tools/virt-qmp-proxy
new file mode 100755
index 0000000000..57f9759fab
--- /dev/null
+++ b/tools/virt-qmp-proxy
@@ -0,0 +1,133 @@
+#!/usr/bin/env python3
+
+import argparse
+import libvirt
+import libvirt_qemu
+import os
+import re
+import socket
+import sys
+import json
+
+
+def get_domain(uri, domstr):
+ conn = libvirt.open(uri)
+
+ dom = None
+ if re.match(r'^\d+$', domstr):
+ dom = conn.lookupByID(int(domstr))
+ elif re.match(r'^[+a-f0-9]+$', domstr):
+ dom = conn.lookupByUUIDString(domstr)
+ else:
+ dom = conn.lookupByName(domstr)
+
+ if not dom.isActive():
+ raise Exception(
+ "Domain must be running to validate measurement")
+
+ return conn, dom
+
+
+def qmp_server(conn, dom, client, verbose):
+ ver = conn.getVersion()
+ major = int(ver / 1000000) % 1000
+ minor = int(ver / 1000) % 1000
+ micro = ver % 1000
+
+ greetingobj = {
+ "QMP": {
+ "version": {
+ "qemu": {
+ "major": major,
+ "minor": minor,
+ "micro": micro,
+ },
+ "package": f"qemu-{major}.{minor}.{micro}",
+ },
+ "capabilities": [
+ "oob"
+ ],
+ }
+ }
+ greeting = json.dumps(greetingobj) + "\r\n"
+ if verbose:
+ print(greeting, end='')
+ client.send(greeting.encode("utf-8"))
+
+ while True:
+ # XXX shouldn't blindly assume this one read
+ # will fully capture one-and-only-one cmd
+ cmd = client.recv(1024).decode('utf8')
+ if verbose:
+ print(cmd)
+
+ if cmd == "":
+ break
+
+ if "qmp_capabilities" in cmd:
+ capabilitiesobj = {
+ "return": {},
+ }
+ capabilities = json.dumps(capabilitiesobj) + "\r\n"
+ if verbose:
+ print(capabilities, end='')
+ client.send(capabilities.encode("utf-8"))
+ continue
+
+ id = None
+ if "id" in cmd:
+ id = cmd[id]
+
+ res = libvirt_qemu.qemuMonitorCommand(dom, cmd, 0)
+
+ resobj = json.loads(res)
+ del resobj["id"]
+ if id is not None:
+ resobj["id"] = id
+ res = json.dumps(resobj) + "\r\n"
+ if verbose:
+ print(res, end='')
+
+ client.send(res.encode('utf8'))
+
+
+def parse_commandline():
+ parser = argparse.ArgumentParser(description="Libvirt QMP proxy")
+ parser.add_argument("--connect", "-c",
+ help="Libvirt QEMU driver connection URI")
+ parser.add_argument("--verbose", "-v", action='store_true',
+ help="Display QMP traffic")
+ parser.add_argument("domain", metavar="DOMAIN",
+ help="Libvirt guest domain ID/UUID/Name")
+ parser.add_argument("sockpath", metavar="QMP-SOCK-PATH",
+ help="UNIX socket path for QMP server")
+
+ return parser.parse_args()
+
+
+def main():
+ args = parse_commandline()
+
+ conn, dom = get_domain(args.connect, args.domain)
+
+ if conn.getType() != "QEMU":
+ raise Exception("QMP proxy requires a QEMU driver connection not %s" %
+ conn.getType())
+
+ sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+ if os.path.exists(args.sockpath):
+ os.unlink(args.sockpath)
+ sock.bind(args.sockpath)
+ sock.listen(1)
+
+ while True:
+ client, peeraddr = sock.accept()
+ qmp_server(conn, dom, client, args.verbose)
+
+
+try:
+ main()
+ sys.exit(0)
+except Exception as e:
+ print("%s: %s" % (sys.argv[0], str(e)))
+ sys.exit(1)
--
2.36.1
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