python/qemu/qmp.py

   1 """ QEMU Monitor Protocol Python class """
   2 # Copyright (C) 2009, 2010 Red Hat Inc.
   3 #
   4 # Authors:
   5 #  Luiz Capitulino <lcapitulino@redhat.com>
   6 #
   7 # This work is licensed under the terms of the GNU GPL, version 2.  See
   8 # the COPYING file in the top-level directory.
   9
  10 import json
  11 import errno
  12 import socket
  13 import logging
  14
  15
  16 class QMPError(Exception):
  17     """
  18     QMP base exception
  19     """
  20
  21
  22 class QMPConnectError(QMPError):
  23     """
  24     QMP connection exception
  25     """
  26
  27
  28 class QMPCapabilitiesError(QMPError):
  29     """
  30     QMP negotiate capabilities exception
  31     """
  32
  33
  34 class QMPTimeoutError(QMPError):
  35     """
  36     QMP timeout exception
  37     """
  38
  39
  40 class QEMUMonitorProtocol:
  41     """
  42     Provide an API to connect to QEMU via QEMU Monitor Protocol (QMP) and then
  43     allow to handle commands and events.
  44     """
  45
  46     #: Logger object for debugging messages
  47     logger = logging.getLogger('QMP')
  48
  49     def __init__(self, address, server=False):
  50         """
  51         Create a QEMUMonitorProtocol class.
  52
  53         @param address: QEMU address, can be either a unix socket path (string)
  54                         or a tuple in the form ( address, port ) for a TCP
  55                         connection
  56         @param server: server mode listens on the socket (bool)
  57         @raise OSError on socket connection errors
  58         @note No connection is established, this is done by the connect() or
  59               accept() methods
  60         """
  61         self.__events = []
  62         self.__address = address
  63         self.__sock = self.__get_sock()
  64         self.__sockfile = None
  65         if server:
  66             self.__sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  67             self.__sock.bind(self.__address)
  68             self.__sock.listen(1)
  69
  70     def __get_sock(self):
  71         if isinstance(self.__address, tuple):
  72             family = socket.AF_INET
  73         else:
  74             family = socket.AF_UNIX
  75         return socket.socket(family, socket.SOCK_STREAM)
  76
  77     def __negotiate_capabilities(self):
  78         greeting = self.__json_read()
  79         if greeting is None or "QMP" not in greeting:
  80             raise QMPConnectError
  81         # Greeting seems ok, negotiate capabilities
  82         resp = self.cmd('qmp_capabilities')
  83         if resp and "return" in resp:
  84             return greeting
  85         raise QMPCapabilitiesError
  86
  87     def __json_read(self, only_event=False):
  88         while True:
  89             data = self.__sockfile.readline()
  90             if not data:
  91                 return None
  92             resp = json.loads(data)
  93             if 'event' in resp:
  94                 self.logger.debug("<<< %s", resp)
  95                 self.__events.append(resp)
  96                 if not only_event:
  97                     continue
  98             return resp
  99
 100     def __get_events(self, wait=False):
 101         """
 102         Check for new events in the stream and cache them in __events.
 103
 104         @param wait (bool): block until an event is available.
 105         @param wait (float): If wait is a float, treat it as a timeout value.
 106
 107         @raise QMPTimeoutError: If a timeout float is provided and the timeout
 108                                 period elapses.
 109         @raise QMPConnectError: If wait is True but no events could be
 110                                 retrieved or if some other error occurred.
 111         """
 112
 113         # Check for new events regardless and pull them into the cache:
 114         self.__sock.setblocking(0)
 115         try:
 116             self.__json_read()
 117         except OSError as err:
 118             if err.errno == errno.EAGAIN:
 119                 # No data available
 120                 pass
 121         self.__sock.setblocking(1)
 122
 123         # Wait for new events, if needed.
 124         # if wait is 0.0, this means "no wait" and is also implicitly false.
 125         if not self.__events and wait:
 126             if isinstance(wait, float):
 127                 self.__sock.settimeout(wait)
 128             try:
 129                 ret = self.__json_read(only_event=True)
 130             except socket.timeout:
 131                 raise QMPTimeoutError("Timeout waiting for event")
 132             except:
 133                 raise QMPConnectError("Error while reading from socket")
 134             if ret is None:
 135                 raise QMPConnectError("Error while reading from socket")
 136             self.__sock.settimeout(None)
 137
 138     def __enter__(self):
 139         # Implement context manager enter function.
 140         return self
 141
 142     def __exit__(self, exc_type, exc_value, exc_traceback):
 143         # Implement context manager exit function.
 144         self.close()
 145         return False
 146
 147     def connect(self, negotiate=True):
 148         """
 149         Connect to the QMP Monitor and perform capabilities negotiation.
 150
 151         @return QMP greeting dict, or None if negotiate is false
 152         @raise OSError on socket connection errors
 153         @raise QMPConnectError if the greeting is not received
 154         @raise QMPCapabilitiesError if fails to negotiate capabilities
 155         """
 156         self.__sock.connect(self.__address)
 157         self.__sockfile = self.__sock.makefile()
 158         if negotiate:
 159             return self.__negotiate_capabilities()
 160         return None
 161
 162     def accept(self, timeout=15.0):
 163         """
 164         Await connection from QMP Monitor and perform capabilities negotiation.
 165
 166         @param timeout: timeout in seconds (nonnegative float number, or
 167                         None). The value passed will set the behavior of the
 168                         underneath QMP socket as described in [1]. Default value
 169                         is set to 15.0.
 170         @return QMP greeting dict
 171         @raise OSError on socket connection errors
 172         @raise QMPConnectError if the greeting is not received
 173         @raise QMPCapabilitiesError if fails to negotiate capabilities
 174
 175         [1]
 176         https://docs.python.org/3/library/socket.html#socket.socket.settimeout
 177         """
 178         self.__sock.settimeout(timeout)
 179         self.__sock, _ = self.__sock.accept()
 180         self.__sockfile = self.__sock.makefile()
 181         return self.__negotiate_capabilities()
 182
 183     def cmd_obj(self, qmp_cmd):
 184         """
 185         Send a QMP command to the QMP Monitor.
 186
 187         @param qmp_cmd: QMP command to be sent as a Python dict
 188         @return QMP response as a Python dict or None if the connection has
 189                 been closed
 190         """
 191         self.logger.debug(">>> %s", qmp_cmd)
 192         try:
 193             self.__sock.sendall(json.dumps(qmp_cmd).encode('utf-8'))
 194         except OSError as err:
 195             if err.errno == errno.EPIPE:
 196                 return None
 197             raise err
 198         resp = self.__json_read()
 199         self.logger.debug("<<< %s", resp)
 200         return resp
 201
 202     def cmd(self, name, args=None, cmd_id=None):
 203         """
 204         Build a QMP command and send it to the QMP Monitor.
 205
 206         @param name: command name (string)
 207         @param args: command arguments (dict)
 208         @param cmd_id: command id (dict, list, string or int)
 209         """
 210         qmp_cmd = {'execute': name}
 211         if args:
 212             qmp_cmd['arguments'] = args
 213         if cmd_id:
 214             qmp_cmd['id'] = cmd_id
 215         return self.cmd_obj(qmp_cmd)
 216
 217     def command(self, cmd, **kwds):
 218         """
 219         Build and send a QMP command to the monitor, report errors if any
 220         """
 221         ret = self.cmd(cmd, kwds)
 222         if "error" in ret:
 223             raise Exception(ret['error']['desc'])
 224         return ret['return']
 225
 226     def pull_event(self, wait=False):
 227         """
 228         Pulls a single event.
 229
 230         @param wait (bool): block until an event is available.
 231         @param wait (float): If wait is a float, treat it as a timeout value.
 232
 233         @raise QMPTimeoutError: If a timeout float is provided and the timeout
 234                                 period elapses.
 235         @raise QMPConnectError: If wait is True but no events could be
 236                                 retrieved or if some other error occurred.
 237
 238         @return The first available QMP event, or None.
 239         """
 240         self.__get_events(wait)
 241
 242         if self.__events:
 243             return self.__events.pop(0)
 244         return None
 245
 246     def get_events(self, wait=False):
 247         """
 248         Get a list of available QMP events.
 249
 250         @param wait (bool): block until an event is available.
 251         @param wait (float): If wait is a float, treat it as a timeout value.
 252
 253         @raise QMPTimeoutError: If a timeout float is provided and the timeout
 254                                 period elapses.
 255         @raise QMPConnectError: If wait is True but no events could be
 256                                 retrieved or if some other error occurred.
 257
 258         @return The list of available QMP events.
 259         """
 260         self.__get_events(wait)
 261         return self.__events
 262
 263     def clear_events(self):
 264         """
 265         Clear current list of pending events.
 266         """
 267         self.__events = []
 268
 269     def close(self):
 270         """
 271         Close the socket and socket file.
 272         """
 273         if self.__sock:
 274             self.__sock.close()
 275         if self.__sockfile:
 276             self.__sockfile.close()
 277
 278     def settimeout(self, timeout):
 279         """
 280         Set the socket timeout.
 281
 282         @param timeout (float): timeout in seconds, or None.
 283         @note This is a wrap around socket.settimeout
 284         """
 285         self.__sock.settimeout(timeout)
 286
 287     def get_sock_fd(self):
 288         """
 289         Get the socket file descriptor.
 290
 291         @return The file descriptor number.
 292         """
 293         return self.__sock.fileno()
 294
 295     def is_scm_available(self):
 296         """
 297         Check if the socket allows for SCM_RIGHTS.
 298
 299         @return True if SCM_RIGHTS is available, otherwise False.
 300         """
 301         return self.__sock.family == socket.AF_UNIX