[PATCH v2 1/2] python: introduce qmp-shell-wrap convenience tool

["Daniel P. Berrangé" <berrange@redhat.com>]

With the current 'qmp-shell' tool developers must first spawn QEMU with
a suitable -qmp arg and then spawn qmp-shell in a separate terminal
pointing to the right socket.

With 'qmp-shell-wrap' developers can ignore QMP sockets entirely and
just pass the QEMU command and arguments they want. The program will
listen on a UNIX socket and tell QEMU to connect QMP to that.

For example, this:

 # qmp-shell-wrap -- qemu-system-x86_64 -display none

Is roughly equivalent of running:

 # qemu-system-x86_64 -display none -qmp qmp-shell-1234 &
 # qmp-shell qmp-shell-1234

Except that 'qmp-shell-wrap' switches the socket peers around so that
it is the UNIX socket server and QEMU is the socket client. This makes
QEMU reliably go away when qmp-shell-wrap exits, closing the server
socket.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 python/qemu/qmp/qmp_shell.py | 67 +++++++++++++++++++++++++++++++++---
 scripts/qmp/qmp-shell-wrap   | 11 ++++++
 2 files changed, 74 insertions(+), 4 deletions(-)
 create mode 100755 scripts/qmp/qmp-shell-wrap

diff --git a/python/qemu/qmp/qmp_shell.py b/python/qemu/qmp/qmp_shell.py
index e7d7eb18f1..fb9e7701af 100644
--- a/python/qemu/qmp/qmp_shell.py
+++ b/python/qemu/qmp/qmp_shell.py
@@ -86,6 +86,7 @@
 import os
 import re
 import readline
+from subprocess import Popen
 import sys
 from typing import (
     Iterator,
@@ -162,8 +163,10 @@ class QMPShell(qmp.QEMUMonitorProtocol):
     :param verbose: Echo outgoing QMP messages to console.
     """
     def __init__(self, address: qmp.SocketAddrT,
-                 pretty: bool = False, verbose: bool = False):
-        super().__init__(address)
+                 pretty: bool = False,
+                 verbose: bool = False,
+                 server: bool = False):
+        super().__init__(address, server=server)
         self._greeting: Optional[QMPMessage] = None
         self._completer = QMPCompleter()
         self._transmode = False
@@ -404,8 +407,10 @@ class HMPShell(QMPShell):
     :param verbose: Echo outgoing QMP messages to console.
     """
     def __init__(self, address: qmp.SocketAddrT,
-                 pretty: bool = False, verbose: bool = False):
-        super().__init__(address, pretty, verbose)
+                 pretty: bool = False,
+                 verbose: bool = False,
+                 server: bool = False):
+        super().__init__(address, pretty, verbose, server)
         self._cpu_index = 0
 
     def _cmd_completion(self) -> None:
@@ -530,5 +535,59 @@ def main() -> None:
             pass
 
 
+def main_wrap() -> None:
+    """
+    qmp-shell-wrap entry point: parse command line arguments and
+    start the REPL.
+    """
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-H', '--hmp', action='store_true',
+                        help='Use HMP interface')
+    parser.add_argument('-v', '--verbose', action='store_true',
+                        help='Verbose (echo commands sent and received)')
+    parser.add_argument('-p', '--pretty', action='store_true',
+                        help='Pretty-print JSON')
+
+    parser.add_argument('command', nargs=argparse.REMAINDER,
+                        help='QEMU command line to invoke')
+
+    args = parser.parse_args()
+
+    cmd = args.command
+    if len(cmd) != 0 and cmd[0] == '--':
+        cmd = cmd[1:]
+    if len(cmd) == 0:
+        cmd = ["qemu-system-x86_64"]
+
+    sockpath = "qmp-shell-wrap-%d" % os.getpid()
+    cmd += ["-qmp", "unix:%s" % sockpath]
+
+    shell_class = HMPShell if args.hmp else QMPShell
+
+    try:
+        address = shell_class.parse_address(sockpath)
+    except qmp.QMPBadPortError:
+        parser.error(f"Bad port number: {sockpath}")
+        return  # pycharm doesn't know error() is noreturn
+
+    try:
+        with shell_class(address, args.pretty, args.verbose, True) as qemu:
+            with Popen(cmd):
+
+                try:
+                    qemu.accept()
+                except qmp.QMPConnectError:
+                    die("Didn't get QMP greeting message")
+                except qmp.QMPCapabilitiesError:
+                    die("Couldn't negotiate capabilities")
+                except OSError as err:
+                    die(f"Couldn't connect to {sockpath}: {err!s}")
+
+                for _ in qemu.repl():
+                    pass
+    finally:
+        os.unlink(sockpath)
+
+
 if __name__ == '__main__':
     main()
diff --git a/scripts/qmp/qmp-shell-wrap b/scripts/qmp/qmp-shell-wrap
new file mode 100755
index 0000000000..9e94da114f
--- /dev/null
+++ b/scripts/qmp/qmp-shell-wrap
@@ -0,0 +1,11 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+
+sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'python'))
+from qemu.qmp import qmp_shell
+
+
+if __name__ == '__main__':
+    qmp_shell.main_wrap()
-- 
2.33.1