Created a XenAPI plugin that will allow nova code to read/write/delete from xenstore records for a given instance. Added the basic methods for working with xenstore data to the vmops script, as well as plugin support to xenapi_conn.py

4 files changed, 410 insertions, 40 deletions

diff --git a/nova/virt/xenapi/vmops.py b/nova/virt/xenapi/vmops.py
index 76f31635a..b6d620782 100644
--- a/nova/virt/xenapi/vmops.py
+++ b/nova/virt/xenapi/vmops.py
@@ -1,6 +1,7 @@
 # vim: tabstop=4 shiftwidth=4 softtabstop=4
 
 # Copyright (c) 2010 Citrix Systems, Inc.
+# Copyright 2010 OpenStack LLC.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License"); you may
 #    not use this file except in compliance with the License. You may obtain
@@ -18,6 +19,7 @@
 Management class for VM-related functions (spawn, reboot, etc).
 """
 
+import json
 import logging
 
 from nova import db
@@ -36,7 +38,6 @@ class VMOps(object):
     """
     Management class for VM-related tasks
     """
-
     def __init__(self, session):
         self.XenAPI = session.get_imported_xenapi()
         self._session = session
@@ -120,6 +121,20 @@ class VMOps(object):
         timer.f = _wait_for_boot
         return timer.start(interval=0.5, now=True)
 
+    def _get_vm_opaque_ref(self, instance_or_vm):
+        """Refactored out the common code of many methods that receive either
+        a vm name or a vm instance, and want a vm instance in return.
+        """
+        try:
+            instance_name = instance_or_vm.name
+            vm = VMHelper.lookup(self._session, instance_name)
+        except AttributeError:
+            # A vm opaque ref was passed
+            vm = instance_or_vm
+        if vm is None:
+            raise Exception(_('Instance not present %s') % instance_name)
+        return vm
+
     def snapshot(self, instance, name):
         """ Create snapshot from a running VM instance
 
@@ -168,11 +183,7 @@ class VMOps(object):
 
     def reboot(self, instance):
         """Reboot VM instance"""
-        instance_name = instance.name
-        vm = VMHelper.lookup(self._session, instance_name)
-        if vm is None:
-            raise exception.NotFound(_('instance not'
-                                       ' found %s') % instance_name)
+        vm = self._get_vm_opaque_ref(instance)
         task = self._session.call_xenapi('Async.VM.clean_reboot', vm)
         self._session.wait_for_task(instance.id, task)
 
@@ -215,27 +226,19 @@ class VMOps(object):
         ret = None
         try:
             ret = self._session.wait_for_task(instance_id, task)
-        except XenAPI.Failure, exc:
+        except self.XenAPI.Failure, exc:
             logging.warn(exc)
         callback(ret)
 
     def pause(self, instance, callback):
         """Pause VM instance"""
-        instance_name = instance.name
-        vm = VMHelper.lookup(self._session, instance_name)
-        if vm is None:
-            raise exception.NotFound(_('Instance not'
-                                       ' found %s') % instance_name)
+        vm = self._get_vm_opaque_ref(instance)
         task = self._session.call_xenapi('Async.VM.pause', vm)
         self._wait_with_callback(instance.id, task, callback)
 
     def unpause(self, instance, callback):
         """Unpause VM instance"""
-        instance_name = instance.name
-        vm = VMHelper.lookup(self._session, instance_name)
-        if vm is None:
-            raise exception.NotFound(_('Instance not'
-                                       ' found %s') % instance_name)
+        vm = self._get_vm_opaque_ref(instance)
         task = self._session.call_xenapi('Async.VM.unpause', vm)
         self._wait_with_callback(instance.id, task, callback)
 
@@ -270,10 +273,7 @@ class VMOps(object):
 
     def get_diagnostics(self, instance):
         """Return data about VM diagnostics"""
-        vm = VMHelper.lookup(self._session, instance.name)
-        if vm is None:
-            raise exception.NotFound(_("Instance not found %s") %
-                instance.name)
+        vm = self._get_vm_opaque_ref(instance)
         rec = self._session.get_xenapi().VM.get_record(vm)
         return VMHelper.compile_diagnostics(self._session, rec)
 
@@ -281,3 +281,175 @@ class VMOps(object):
         """Return snapshot of console"""
         # TODO: implement this to fix pylint!
         return 'FAKE CONSOLE OUTPUT of instance'
+
+    def list_from_xenstore(self, vm, path):
+        """Runs the xenstore-ls command to get a listing of all records
+        from 'path' downward. Returns a dict with the sub-paths as keys,
+        and the value stored in those paths as values. If nothing is
+        found at that path, returns None.
+        """
+        ret = self._make_xenstore_call('list_records', vm, path)
+        return json.loads(ret)
+
+    def read_from_xenstore(self, vm, path):
+        """Returns the value stored in the xenstore record for the given VM
+        at the specified location. A XenAPIPlugin.PluginError will be raised
+        if any error is encountered in the read process.
+        """
+        try:
+            ret = self._make_xenstore_call('read_record', vm, path,
+                    {'ignore_missing_path': 'True'})
+        except self.XenAPI.Failure, e:
+            return None
+        ret = json.loads(ret)
+        if ret == "None":
+            # Can't marshall None over RPC calls.
+            return None
+        return ret
+
+    def write_to_xenstore(self, vm, path, value):
+        """Writes the passed value to the xenstore record for the given VM
+        at the specified location. A XenAPIPlugin.PluginError will be raised
+        if any error is encountered in the write process.
+        """
+        return self._make_xenstore_call('write_record', vm, path,
+                {'value': json.dumps(value)})
+
+    def clear_xenstore(self, vm, path):
+        """Deletes the VM's xenstore record for the specified path.
+        If there is no such record, the request is ignored.
+        """
+        self._make_xenstore_call('delete_record', vm, path)
+
+    def _make_xenstore_call(self, method, vm, path, addl_args={}):
+        """Handles calls to the xenstore xenapi plugin."""
+        return self._make_plugin_call('xenstore.py', method=method, vm=vm,
+                path=path, addl_args=addl_args)
+
+    def _make_plugin_call(self, plugin, method, vm, path, addl_args={}):
+        """Abstracts out the process of calling a method of a xenapi plugin.
+        Any errors raised by the plugin will in turn raise a RuntimeError here.
+        """
+        vm = self._get_vm_opaque_ref(vm)
+        rec = self._session.get_xenapi().VM.get_record(vm)
+        args = {'dom_id': rec['domid'], 'path': path}
+        args.update(addl_args)
+        # If the 'testing_mode' attribute is set, add that to the args.
+        if getattr(self, 'testing_mode', False):
+            args['testing_mode'] = 'true'
+        try:
+            task = self._session.async_call_plugin(plugin, method, args)
+            ret = self._session.wait_for_task(0, task)
+        except self.XenAPI.Failure, e:
+            raise RuntimeError("%s" % e.details[-1])
+        return ret
+
+    def add_to_xenstore(self, vm, path, key, value):
+        """Adds the passed key/value pair to the xenstore record for
+        the given VM at the specified location. A XenAPIPlugin.PluginError
+        will be raised if any error is encountered in the write process.
+        """
+        current = self.read_from_xenstore(vm, path)
+        if not current:
+            # Nothing at that location
+            current = {key: value}
+        else:
+            current[key] = value
+        self.write_to_xenstore(vm, path, current)
+
+    def remove_from_xenstore(self, vm, path, key_or_keys):
+        """Takes either a single key or a list of keys and removes
+        them from the xenstoreirecord data for the given VM.
+        If the key doesn't exist, the request is ignored.
+        """
+        current = self.list_from_xenstore(vm, path)
+        if not current:
+            return
+        if isinstance(key_or_keys, basestring):
+            keys = [key_or_keys]
+        else:
+            keys = key_or_keys
+        keys.sort(lambda x, y: cmp(y.count('/'), x.count('/')))
+        for key in keys:
+            if path:
+                keypath = "%s/%s" % (path, key)
+            else:
+                keypath = key
+            self._make_xenstore_call('delete_record', vm, keypath)
+
+    ########################################################################
+    ###### The following methods interact with the xenstore parameter
+    ###### record, not the live xenstore. They were created before I
+    ###### knew the difference, and are left in here in case they prove
+    ###### to be useful. They all have '_param' added to their method
+    ###### names to distinguish them. (dabo)
+    ########################################################################
+    def read_partial_from_param_xenstore(self, instance_or_vm, key_prefix):
+        """Returns a dict of all the keys in the xenstore parameter record
+        for the given instance that begin with the key_prefix.
+        """
+        data = self.read_from_param_xenstore(instance_or_vm)
+        badkeys = [k for k in data.keys()
+                if not k.startswith(key_prefix)]
+        for badkey in badkeys:
+            del data[badkey]
+        return data
+
+    def read_from_param_xenstore(self, instance_or_vm, keys=None):
+        """Returns the xenstore parameter record data for the specified VM
+        instance as a dict. Accepts an optional key or list of keys; if a
+        value for 'keys' is passed, the returned dict is filtered to only
+        return the values for those keys.
+        """
+        vm = self._get_vm_opaque_ref(instance_or_vm)
+        data = self._session.call_xenapi_request('VM.get_xenstore_data',
+                (vm, ))
+        ret = {}
+        if keys is None:
+            keys = data.keys()
+        elif isinstance(keys, basestring):
+            keys = [keys]
+        for key in keys:
+            raw = data.get(key)
+            if raw:
+                ret[key] = json.loads(raw)
+            else:
+                ret[key] = raw
+        return ret
+
+    def add_to_param_xenstore(self, instance_or_vm, key, val):
+        """Takes a key/value pair and adds it to the xenstore parameter
+        record for the given vm instance. If the key exists in xenstore,
+        it is overwritten"""
+        vm = self._get_vm_opaque_ref(instance_or_vm)
+        self.remove_from_param_xenstore(instance_or_vm, key)
+        jsonval = json.dumps(val)
+        self._session.call_xenapi_request('VM.add_to_xenstore_data',
+                (vm, key, jsonval))
+
+    def write_to_param_xenstore(self, instance_or_vm, mapping):
+        """Takes a dict and writes each key/value pair to the xenstore
+        parameter record for the given vm instance. Any existing data for
+        those keys is overwritten.
+        """
+        for k, v in mapping.iteritems():
+            self.add_to_param_xenstore(instance_or_vm, k, v)
+
+    def remove_from_param_xenstore(self, instance_or_vm, key_or_keys):
+        """Takes either a single key or a list of keys and removes
+        them from the xenstore parameter record data for the given VM.
+        If the key doesn't exist, the request is ignored.
+        """
+        vm = self._get_vm_opaque_ref(instance_or_vm)
+        if isinstance(key_or_keys, basestring):
+            keys = [key_or_keys]
+        else:
+            keys = key_or_keys
+        for key in keys:
+            self._session.call_xenapi_request('VM.remove_from_xenstore_data',
+                    (vm, key))
+
+    def clear_param_xenstore(self, instance_or_vm):
+        """Removes all data from the xenstore parameter record for this VM."""
+        self.write_to_param_xenstore(instance_or_vm, {})
+    ########################################################################
diff --git a/nova/virt/xenapi_conn.py b/nova/virt/xenapi_conn.py
index f17c8f39d..c48f5b7cb 100644
--- a/nova/virt/xenapi_conn.py
+++ b/nova/virt/xenapi_conn.py
@@ -1,6 +1,7 @@
 # vim: tabstop=4 shiftwidth=4 softtabstop=4
 
 # Copyright (c) 2010 Citrix Systems, Inc.
+# Copyright 2010 OpenStack LLC.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License"); you may
 #    not use this file except in compliance with the License. You may obtain
@@ -19,15 +20,15 @@ A connection to XenServer or Xen Cloud Platform.
 
 The concurrency model for this class is as follows:
 
-All XenAPI calls are on a thread (using t.i.t.deferToThread, via the decorator
-deferredToThread).  They are remote calls, and so may hang for the usual
-reasons.  They should not be allowed to block the reactor thread.
+All XenAPI calls are on a green thread (using eventlet's "tpool"
+thread pool). They are remote calls, and so may hang for the usual
+reasons.
 
 All long-running XenAPI calls (VM.start, VM.reboot, etc) are called async
-(using XenAPI.VM.async_start etc).  These return a task, which can then be
-polled for completion.  Polling is handled using reactor.callLater.
+(using XenAPI.VM.async_start etc). These return a task, which can then be
+polled for completion.
 
-This combination of techniques means that we don't block the reactor thread at
+This combination of techniques means that we don't block the main thread at
 all, and at the same time we don't hold lots of threads waiting for
 long-running operations.
 
@@ -81,7 +82,7 @@ flags.DEFINE_string('xenapi_connection_password',
 flags.DEFINE_float('xenapi_task_poll_interval',
                    0.5,
                    'The interval used for polling of remote tasks '
-                   '(Async.VM.start, etc).  Used only if '
+                   '(Async.VM.start, etc). Used only if '
                    'connection_type=xenapi.')
 flags.DEFINE_float('xenapi_vhd_coalesce_poll_interval',
                    5.0,
@@ -213,6 +214,14 @@ class XenAPISession(object):
             f = f.__getattr__(m)
         return tpool.execute(f, *args)
 
+    def call_xenapi_request(self, method, *args):
+        """Some interactions with dom0, such as interacting with xenstore's
+        param record, require using the xenapi_request method of the session
+        object. This wraps that call on a background thread.
+        """
+        f = self._session.xenapi_request
+        return tpool.execute(f, method, *args)
+
     def async_call_plugin(self, plugin, fn, args):
         """Call Async.host.call_plugin on a background thread."""
         return tpool.execute(self._unwrap_plugin_exceptions,
@@ -222,7 +231,6 @@ class XenAPISession(object):
     def wait_for_task(self, id, task):
         """Return the result of the given task. The task is polled
         until it completes."""
-
         done = event.Event()
         loop = utils.LoopingCall(self._poll_task, id, task, done)
         loop.start(FLAGS.xenapi_task_poll_interval, now=True)
@@ -235,7 +243,7 @@ class XenAPISession(object):
         return self.XenAPI.Session(url)
 
     def _poll_task(self, id, task, done):
-        """Poll the given XenAPI task, and fire the given Deferred if we
+        """Poll the given XenAPI task, and fire the given action if we
         get a result."""
         try:
             name = self._session.xenapi.task.get_name_label(task)
@@ -290,7 +298,7 @@ class XenAPISession(object):
 
 
 def _parse_xmlrpc_value(val):
-    """Parse the given value as if it were an XML-RPC value.  This is
+    """Parse the given value as if it were an XML-RPC value. This is
     sometimes used as the format for the task.result field."""
     if not val:
         return val
diff --git a/plugins/xenserver/xenapi/etc/xapi.d/plugins/pluginlib_nova.py b/plugins/xenserver/xenapi/etc/xapi.d/plugins/pluginlib_nova.py
index 2d323a016..8e7a829d5 100755
--- a/plugins/xenserver/xenapi/etc/xapi.d/plugins/pluginlib_nova.py
+++ b/plugins/xenserver/xenapi/etc/xapi.d/plugins/pluginlib_nova.py
@@ -45,6 +45,7 @@ class PluginError(Exception):
     def __init__(self, *args):
         Exception.__init__(self, *args)
 
+
 class ArgumentError(PluginError):
     """Raised when required arguments are missing, argument values are invalid,
     or incompatible arguments are given.
@@ -67,6 +68,7 @@ def ignore_failure(func, *args, **kwargs):
 
 ARGUMENT_PATTERN = re.compile(r'^[a-zA-Z0-9_:\.\-,]+$')
 
+
 def validate_exists(args, key, default=None):
     """Validates that a string argument to a RPC method call is given, and
     matches the shell-safe regex, with an optional default value in case it
@@ -76,20 +78,24 @@ def validate_exists(args, key, default=None):
     """
     if key in args:
         if len(args[key]) == 0:
-            raise ArgumentError('Argument %r value %r is too short.' % (key, args[key]))
+            raise ArgumentError('Argument %r value %r is too short.' %
+                    (key, args[key]))
         if not ARGUMENT_PATTERN.match(args[key]):
-            raise ArgumentError('Argument %r value %r contains invalid characters.' % (key, args[key]))
+            raise ArgumentError('Argument %r value %r contains invalid '
+                    'characters.' % (key, args[key]))
         if args[key][0] == '-':
-            raise ArgumentError('Argument %r value %r starts with a hyphen.' % (key, args[key]))
+            raise ArgumentError('Argument %r value %r starts with a hyphen.'
+                    % (key, args[key]))
         return args[key]
     elif default is not None:
         return default
     else:
         raise ArgumentError('Argument %s is required.' % key)
 
+
 def validate_bool(args, key, default=None):
-    """Validates that a string argument to a RPC method call is a boolean string,
-    with an optional default value in case it does not exist.
+    """Validates that a string argument to a RPC method call is a boolean
+    string, with an optional default value in case it does not exist.
 
     Returns the python boolean value.
     """
@@ -99,7 +105,9 @@ def validate_bool(args, key, default=None):
     elif value.lower() == 'false':
         return False
     else:
-        raise ArgumentError("Argument %s may not take value %r. Valid values are ['true', 'false']." % (key, value))
+        raise ArgumentError("Argument %s may not take value %r. "
+                "Valid values are ['true', 'false']." % (key, value))
+
 
 def exists(args, key):
     """Validates that a freeform string argument to a RPC method call is given.
@@ -110,6 +118,7 @@ def exists(args, key):
     else:
         raise ArgumentError('Argument %s is required.' % key)
 
+
 def optional(args, key):
     """If the given key is in args, return the corresponding value, otherwise
     return None"""
@@ -122,13 +131,14 @@ def get_this_host(session):
 
 def get_domain_0(session):
     this_host_ref = get_this_host(session)
-    expr = 'field "is_control_domain" = "true" and field "resident_on" = "%s"' % this_host_ref
+    expr = 'field "is_control_domain" = "true" and field "resident_on" = "%s"'
+    expr = expr % this_host_ref
     return session.xenapi.VM.get_all_records_where(expr).keys()[0]
 
 
 def create_vdi(session, sr_ref, name_label, virtual_size, read_only):
     vdi_ref = session.xenapi.VDI.create(
-        { 'name_label': name_label,
+         {'name_label': name_label,
           'name_description': '',
           'SR': sr_ref,
           'virtual_size': str(virtual_size),
@@ -138,7 +148,7 @@ def create_vdi(session, sr_ref, name_label, virtual_size, read_only):
           'xenstore_data': {},
           'other_config': {},
           'sm_config': {},
-          'tags': [] })
+          'tags': []})
     logging.debug('Created VDI %s (%s, %s, %s) on %s.', vdi_ref, name_label,
                   virtual_size, read_only, sr_ref)
     return vdi_ref
diff --git a/plugins/xenserver/xenapi/etc/xapi.d/plugins/xenstore.py b/plugins/xenserver/xenapi/etc/xapi.d/plugins/xenstore.py
new file mode 100755
index 000000000..695bf3448
--- /dev/null
+++ b/plugins/xenserver/xenapi/etc/xapi.d/plugins/xenstore.py
@@ -0,0 +1,180 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2010 Citrix Systems, Inc.
+# Copyright 2010 OpenStack LLC.
+# Copyright 2010 United States Government as represented by the
+# Administrator of the National Aeronautics and Space Administration.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+#
+# XenAPI plugin for reading/writing information to xenstore
+#
+
+try:
+    import json
+except ImportError:
+    import simplejson as json
+import subprocess
+
+import XenAPIPlugin
+
+import pluginlib_nova as pluginlib
+pluginlib.configure_logging("xenstore")
+
+
+def jsonify(fnc):
+    def wrapper(*args, **kwargs):
+        return json.dumps(fnc(*args, **kwargs))
+    return wrapper
+
+
+@jsonify
+def read_record(self, arg_dict):
+    """Returns the value stored at the given path for the given dom_id.
+    These must be encoded as key/value pairs in arg_dict. You can
+    optinally include a key 'ignore_missing_path'; if this is present
+    and boolean True, attempting to read a non-existent path will return
+    the string 'None' instead of raising an exception.
+    """
+    cmd = "xenstore-read /local/domain/%(dom_id)s/%(path)s" % arg_dict
+    try:
+        return _run_command(cmd).rstrip("\n")
+    except pluginlib.PluginError, e:
+        if arg_dict.get("ignore_missing_path", False):
+            cmd = "xenstore-exists /local/domain/%(dom_id)s/%(path)s; echo $?"
+            cmd = cmd % arg_dict
+            ret = _run_command(cmd).strip()
+            # If the path exists, the cmd should return "0"
+            if ret != "0":
+                # No such path, so ignore the error and return the
+                # string 'None', since None can't be marshalled
+                # over RPC.
+                return "None"
+        # Either we shouldn't ignore path errors, or another
+        # error was hit. Re-raise.
+        raise
+
+
+@jsonify
+def write_record(self, arg_dict):
+    """Writes to xenstore at the specified path. If there is information
+    already stored in that location, it is overwritten. As in read_record,
+    the dom_id and path must be specified in the arg_dict; additionally,
+    you must specify a 'value' key, whose value must be a string. Typically,
+    you can json-ify more complex values and store the json output.
+    """
+    cmd = "xenstore-write /local/domain/%(dom_id)s/%(path)s '%(value)s'"
+    cmd = cmd % arg_dict
+    _run_command(cmd)
+    return arg_dict["value"]
+
+
+@jsonify
+def list_records(self, arg_dict):
+    """Returns all the stored data at or below the given path for the
+    given dom_id. The data is returned as a json-ified dict, with the
+    path as the key and the stored value as the value. If the path
+    doesn't exist, an empty dict is returned.
+    """
+    cmd = "xenstore-ls /local/domain/%(dom_id)s/%(path)s" % arg_dict
+    cmd = cmd.rstrip("/")
+    try:
+        recs = _run_command(cmd)
+    except pluginlib.PluginError, e:
+        if "No such file or directory" in "%s" % e:
+            # Path doesn't exist.
+            return {}
+        return str(e)
+        raise
+    base_path = arg_dict["path"]
+    paths = _paths_from_ls(recs)
+    ret = {}
+    for path in paths:
+        if base_path:
+            arg_dict["path"] = "%s/%s" % (base_path, path)
+        else:
+            arg_dict["path"] = path
+        rec = read_record(self, arg_dict)
+        try:
+            val = json.loads(rec)
+        except ValueError:
+            val = rec
+        ret[path] = val
+    return ret
+
+
+@jsonify
+def delete_record(self, arg_dict):
+    """Just like it sounds: it removes the record for the specified
+    VM and the specified path from xenstore.
+    """
+    cmd = "xenstore-rm /local/domain/%(dom_id)s/%(path)s" % arg_dict
+    return _run_command(cmd)
+
+
+def _paths_from_ls(recs):
+    """The xenstore-ls command returns a listing that isn't terribly
+    useful. This method cleans that up into a dict with each path
+    as the key, and the associated string as the value.
+    """
+    ret = {}
+    last_nm = ""
+    level = 0
+    path = []
+    ret = []
+    for ln in recs.splitlines():
+        nm, val = ln.rstrip().split(" = ")
+        barename = nm.lstrip()
+        this_level = len(nm) - len(barename)
+        if this_level == 0:
+            ret.append(barename)
+            level = 0
+            path = []
+        elif this_level == level:
+            # child of same parent
+            ret.append("%s/%s" % ("/".join(path), barename))
+        elif this_level > level:
+            path.append(last_nm)
+            ret.append("%s/%s" % ("/".join(path), barename))
+            level = this_level
+        elif this_level < level:
+            path = path[:this_level]
+            ret.append("%s/%s" % ("/".join(path), barename))
+            level = this_level
+        last_nm = barename
+    return ret
+
+
+def _run_command(cmd):
+    """Abstracts out the basics of issuing system commands. If the command
+    returns anything in stderr, a PluginError is raised with that information.
+    Otherwise, the output from stdout is returned.
+    """
+    pipe = subprocess.PIPE
+    proc = subprocess.Popen([cmd], shell=True, stdin=pipe, stdout=pipe,
+            stderr=pipe, close_fds=True)
+    proc.wait()
+    err = proc.stderr.read()
+    if err:
+        raise pluginlib.PluginError(err)
+    return proc.stdout.read()
+
+
+if __name__ == "__main__":
+    XenAPIPlugin.dispatch(
+        {"read_record": read_record,
+        "write_record": write_record,
+        "list_records": list_records,
+        "delete_record": delete_record})