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#!/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 logging
import os
import subprocess
import XenAPIPlugin
import pluginlib_nova as pluginlib
pluginlib.configure_logging("xenstore")
class XenstoreError(pluginlib.PluginError):
"""Errors that occur when calling xenstore-* through subprocesses"""
def __init__(self, cmd, return_code, stderr, stdout):
msg = "cmd: %s; returncode: %d; stderr: %s; stdout: %s"
msg = msg % (cmd, return_code, stderr, stdout)
self.cmd = cmd
self.return_code = return_code
self.stderr = stderr
self.stdout = stdout
pluginlib.PluginError.__init__(self, msg)
def jsonify(fnc):
def wrapper(*args, **kwargs):
ret = fnc(*args, **kwargs)
try:
json.loads(ret)
except ValueError:
# Value should already be JSON-encoded, but some operations
# may write raw sting values; this will catch those and
# properly encode them.
ret = json.dumps(ret)
return ret
return wrapper
def _record_exists(arg_dict):
"""Returns whether or not the given record exists. The record path
is determined from the given path and dom_id in the arg_dict."""
cmd = ["xenstore-exists", "/local/domain/%(dom_id)s/%(path)s" % arg_dict]
try:
ret, result = _run_command(cmd)
except XenstoreError, e:
if e.stderr == '':
# if stderr was empty, this just means the path did not exist
return False
# otherwise there was a real problem
raise
return True
@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:
ret, result = _run_command(cmd)
return result.strip()
except XenstoreError, e:
if arg_dict.get("ignore_missing_path", False):
if not _record_exists(arg_dict):
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" % arg_dict,
arg_dict["value"]]
_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.
"""
dirpath = "/local/domain/%(dom_id)s/%(path)s" % arg_dict
cmd = ["xenstore-ls", dirpath.rstrip("/")]
try:
ret, recs = _run_command(cmd)
except XenstoreError, e:
if not _record_exists(arg_dict):
return {}
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]
ret, result = _run_command(cmd)
return result
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, a tuple of (return code, stdout data) is returned.
"""
logging.info(' '.join(cmd))
pipe = subprocess.PIPE
proc = subprocess.Popen(cmd, stdin=pipe, stdout=pipe, stderr=pipe,
close_fds=True)
out, err = proc.communicate()
if proc.returncode is not os.EX_OK:
raise XenstoreError(cmd, proc.returncode, err, out)
return proc.returncode, out
if __name__ == "__main__":
XenAPIPlugin.dispatch(
{"read_record": read_record,
"write_record": write_record,
"list_records": list_records,
"delete_record": delete_record})
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