Re: [RFC PATCH] python: add qmp-send program to send raw qmp commands to qemu

[Daniel P . Berrangé]

On Wed, Mar 16, 2022 at 10:54:55AM +0100, Damien Hedde wrote:


> +def raw_load(file: TextIO) -> List[QMPMessage]:
> +    """parse a raw qmp command file.
> +
> +    JSON formatted commands can expand on several lines but must
> +    be separated by an end-of-line (two commands can not share the
> +    same line).
> +    File must not end with empty lines.
> +    """
> +    cmds: List[QMPMessage] = []
> +    linecnt = 0
> +    while True:
> +        buf = file.readline()
> +        if not buf:
> +            return cmds

If you change this to 'break'...

> +        prev_err_pos = None
> +        buf_linecnt = 1
> +        while True:
> +            try:
> +                cmds.append(json.loads(buf))

...and this to

  yield json.loads(buf)

then....

> +                break
> +            except json.JSONDecodeError as err:
> +                if prev_err_pos == err.pos:
> +                    # adding a line made no progress so
> +                    #  + either we're at EOF and json data is truncated
> +                    #  + or the parsing error is before
> +                    raise QmpRawDecodeError(err.msg, linecnt + err.lineno,
> +                                            err.colno) from err
> +                prev_err_pos = err.pos
> +            buf += file.readline()
> +            buf_linecnt += 1
> +        linecnt += buf_linecnt
> +
> +
> +def report_error(msg: str) -> None:
> +    """Write an error to stderr."""
> +    sys.stderr.write('ERROR: %s\n' % msg)
> +
> +
> +def main() -> None:
> +    """
> +    qmp-send entry point: parse command line arguments and start the REPL.
> +    """
> +    parser = argparse.ArgumentParser(
> +            description="""
> +            Send raw qmp commands to qemu as long as they succeed. It either
> +            connects to a remote qmp server using the provided socket or wrap
> +            the qemu process. It stops sending the provided commands when a
> +            command fails (disconnection or error response).
> +            """,
> +            epilog="""
> +            When qemu wrap option is used, this script waits for qemu
> +            to terminate but never send any quit or kill command. This
> +            needs to be done manually.
> +            """)
> +
> +    parser.add_argument('-f', '--file', action='store',
> +                        help='Input file containing the commands')
> +    parser.add_argument('-s', '--socket', action='store',
> +                        help='< UNIX socket path | TCP address:port >')
> +    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('--wrap', nargs=argparse.REMAINDER,
> +                        help='QEMU command line to invoke')
> +
> +    args = parser.parse_args()
> +
> +    socket = args.socket
> +    wrap_qemu = args.wrap is not None
> +
> +    if wrap_qemu:
> +        if len(args.wrap) != 0:
> +            qemu_cmdline = args.wrap
> +        else:
> +            qemu_cmdline = ["qemu-system-x86_64"]
> +        if socket is None:
> +            socket = "qmp-send-wrap-%d" % os.getpid()
> +        qemu_cmdline += ["-qmp", "unix:%s" % socket]
> +
> +    try:
> +        address = QMPSend.parse_address(socket)
> +    except QMPBadPortError:
> +        parser.error(f"Bad port number: {socket}")
> +        return  # pycharm doesn't know error() is noreturn
> +
> +    try:
> +        with open(args.file, mode='rt', encoding='utf8') as file:
> +            qmp_cmds = raw_load(file)
> +    except QmpRawDecodeError as err:
> +        report_error(str(err))
> +        sys.exit(1)

...change this to

    fh = sys.stdin
    if args.file is not None and args.file != '-':
      fh = open(args.file, mode='rt', encoding='utf8')

....

> +
> +    try:
> +        with QMPSend(address, args.pretty, args.verbose,
> +                     server=wrap_qemu) as qmp:
> +            # starting with python 3.7 we could use contextlib.nullcontext
> +            qemu = Popen(qemu_cmdline) if wrap_qemu else 
> contextlib.suppress()
> +            with qemu:
> +                try:
> +                    qmp.setup_connection()
> +                except ConnectError as err:
> +                    if isinstance(err.exc, OSError):
> +                        report_error(f"Couldn't connect to {socket}: 
> {err!s}")
> +                    else:
> +                        report_error(str(err))
> +                    sys.exit(1)
> +                try:
> +                    for cmd in qmp_cmds:

...finally this to

    for cmd in raw_load(fh)


This means we can use qmp-send in a pipeline with commands
sent to QEMU on the fly as they arrive, rather than having
to read all the commands upfront before QEMU is started.

BTW, as an example usage I was trying your impl here in the following
way to extract information about CPUs that are deprecated

   echo -e '{ "execute": "query-cpu-definitions"}\n{"execute": "quit"}' | \
     qmp-send -v -p --wrap ./build/qemu-system-x86_64 -nodefaults  -vnc :1 | \
     jq -r  --slurp '.[1].return[] | [.name, .deprecated] | @csv' 


> +                        qmp.execute_cmd(cmd)
> +                except QMPError as err:
> +                    report_error(str(err))
> +                    sys.exit(1)
> +    finally:
> +        if wrap_qemu:
> +            os.unlink(socket)
> +
> +
> +if __name__ == '__main__':
> +    main()


With regards,
Daniel
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