openstack/nova
Code Issues Proposed changes
nova/nova/virt/libvirt/imagecache.py
Matthew Booth 547dc45044 Remove deprecated option libvirt.remove_unused_kernels 
This option was deprecated in Grizzly, and explicitly marked for
removal in 13.0.0. We have reached this version, and it complicates
the cleanup of writing to the image cache, so now is the time to
remove it.

Change-Id: Iadfe21c956880d9cbe5c16a1e277e1c5362a5755
2016-05-17 11:09:02 +01:00

634 lines
24 KiB
Python
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# Copyright 2012 Michael Still and Canonical Inc
# 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.
"""Image cache manager.
The cache manager implements the specification at
http://wiki.openstack.org/nova-image-cache-management.
"""
import hashlib
import os
import re
import time
from oslo_concurrency import lockutils
from oslo_concurrency import processutils
from oslo_log import log as logging
from oslo_serialization import jsonutils
from oslo_utils import fileutils
import nova.conf
from nova.i18n import _LE
from nova.i18n import _LI
from nova.i18n import _LW
from nova import utils
from nova.virt import imagecache
from nova.virt.libvirt import utils as libvirt_utils
LOG = logging.getLogger(__name__)
CONF = nova.conf.CONF
def get_cache_fname(image_id):
"""Return a filename based on the SHA1 hash of a given image ID.
Image files stored in the _base directory that match this pattern
are considered for cleanup by the image cache manager. The cache
manager considers the file to be in use if it matches an instance's
image_ref, kernel_id or ramdisk_id property.
"""
return hashlib.sha1(image_id).hexdigest()
def get_info_filename(base_path):
"""Construct a filename for storing additional information about a base
image.
Returns a filename.
"""
base_file = os.path.basename(base_path)
return (CONF.libvirt.image_info_filename_pattern
% {'image': base_file})
def is_valid_info_file(path):
"""Test if a given path matches the pattern for info files."""
digest_size = hashlib.sha1().digestsize * 2
regexp = (CONF.libvirt.image_info_filename_pattern
% {'image': ('([0-9a-f]{%(digest_size)d}|'
'[0-9a-f]{%(digest_size)d}_sm|'
'[0-9a-f]{%(digest_size)d}_[0-9]+)'
% {'digest_size': digest_size})})
m = re.match(regexp, path)
if m:
return True
return False
def _read_possible_json(serialized, info_file):
try:
d = jsonutils.loads(serialized)
except ValueError as e:
LOG.error(_LE('Error reading image info file %(filename)s: '
'%(error)s'),
{'filename': info_file,
'error': e})
d = {}
return d
def read_stored_info(target, field=None, timestamped=False):
"""Read information about an image.
Returns an empty dictionary if there is no info, just the field value if
a field is requested, or the entire dictionary otherwise.
"""
info_file = get_info_filename(target)
if not os.path.exists(info_file):
# NOTE(mikal): Special case to handle essex checksums being converted.
# There is an assumption here that target is a base image filename.
old_filename = target + '.sha1'
if field == 'sha1' and os.path.exists(old_filename):
with open(old_filename) as hash_file:
hash_value = hash_file.read()
write_stored_info(target, field=field, value=hash_value)
os.remove(old_filename)
d = {field: hash_value}
else:
d = {}
else:
lock_name = 'info-%s' % os.path.split(target)[-1]
lock_path = os.path.join(CONF.instances_path, 'locks')
@utils.synchronized(lock_name, external=True, lock_path=lock_path)
def read_file(info_file):
LOG.debug('Reading image info file: %s', info_file)
with open(info_file, 'r') as f:
return f.read().rstrip()
serialized = read_file(info_file)
d = _read_possible_json(serialized, info_file)
if field:
if timestamped:
return (d.get(field, None), d.get('%s-timestamp' % field, None))
else:
return d.get(field, None)
return d
def write_stored_info(target, field=None, value=None):
"""Write information about an image."""
if not field:
return
info_file = get_info_filename(target)
LOG.info(_LI('Writing stored info to %s'), info_file)
fileutils.ensure_tree(os.path.dirname(info_file))
lock_name = 'info-%s' % os.path.split(target)[-1]
lock_path = os.path.join(CONF.instances_path, 'locks')
@utils.synchronized(lock_name, external=True, lock_path=lock_path)
def write_file(info_file, field, value):
d = {}
if os.path.exists(info_file):
with open(info_file, 'r') as f:
d = _read_possible_json(f.read(), info_file)
d[field] = value
d['%s-timestamp' % field] = time.time()
with open(info_file, 'w') as f:
f.write(jsonutils.dumps(d))
write_file(info_file, field, value)
def _hash_file(filename):
"""Generate a hash for the contents of a file."""
checksum = hashlib.sha1()
with open(filename) as f:
for chunk in iter(lambda: f.read(32768), b''):
checksum.update(chunk)
return checksum.hexdigest()
def read_stored_checksum(target, timestamped=True):
"""Read the checksum.
Returns the checksum (as hex) or None.
"""
return read_stored_info(target, field='sha1', timestamped=timestamped)
def write_stored_checksum(target):
"""Write a checksum to disk for a file in _base."""
write_stored_info(target, field='sha1', value=_hash_file(target))
class ImageCacheManager(imagecache.ImageCacheManager):
def __init__(self):
super(ImageCacheManager, self).__init__()
self.lock_path = os.path.join(CONF.instances_path, 'locks')
self._reset_state()
def _reset_state(self):
"""Reset state variables used for each pass."""
self.used_images = {}
self.image_popularity = {}
self.instance_names = set()
self.back_swap_images = set()
self.used_swap_images = set()
self.active_base_files = []
self.corrupt_base_files = []
self.originals = []
self.removable_base_files = []
self.unexplained_images = []
def _store_image(self, base_dir, ent, original=False):
"""Store a base image for later examination."""
entpath = os.path.join(base_dir, ent)
if os.path.isfile(entpath):
self.unexplained_images.append(entpath)
if original:
self.originals.append(entpath)
def _store_swap_image(self, ent):
"""Store base swap images for later examination."""
names = ent.split('_')
if len(names) == 2 and names[0] == 'swap':
if len(names[1]) > 0 and names[1].isdigit():
LOG.debug('Adding %s into backend swap images', ent)
self.back_swap_images.add(ent)
def _list_base_images(self, base_dir):
"""Return a list of the images present in _base.
Determine what images we have on disk. There will be other files in
this directory so we only grab the ones which are the right length
to be disk images.
"""
digest_size = hashlib.sha1().digestsize * 2
for ent in os.listdir(base_dir):
if len(ent) == digest_size:
self._store_image(base_dir, ent, original=True)
elif (len(ent) > digest_size + 2 and
ent[digest_size] == '_' and
not is_valid_info_file(os.path.join(base_dir, ent))):
self._store_image(base_dir, ent, original=False)
else:
self._store_swap_image(ent)
return {'unexplained_images': self.unexplained_images,
'originals': self.originals}
def _list_backing_images(self):
"""List the backing images currently in use."""
inuse_images = []
for ent in os.listdir(CONF.instances_path):
if ent in self.instance_names:
LOG.debug('%s is a valid instance name', ent)
disk_path = os.path.join(CONF.instances_path, ent, 'disk')
if os.path.exists(disk_path):
LOG.debug('%s has a disk file', ent)
try:
backing_file = libvirt_utils.get_disk_backing_file(
disk_path)
except processutils.ProcessExecutionError:
# (for bug 1261442)
if not os.path.exists(disk_path):
LOG.debug('Failed to get disk backing file: %s',
disk_path)
continue
else:
raise
LOG.debug('Instance %(instance)s is backed by '
'%(backing)s',
{'instance': ent,
'backing': backing_file})
if backing_file:
backing_path = os.path.join(
CONF.instances_path,
CONF.image_cache_subdirectory_name,
backing_file)
if backing_path not in inuse_images:
inuse_images.append(backing_path)
if backing_path in self.unexplained_images:
LOG.warning(_LW('Instance %(instance)s is using a '
'backing file %(backing)s which '
'does not appear in the image '
'service'),
{'instance': ent,
'backing': backing_file})
self.unexplained_images.remove(backing_path)
return inuse_images
def _find_base_file(self, base_dir, fingerprint):
"""Find the base file matching this fingerprint.
Yields the name of the base file, a boolean which is True if the image
is "small", and a boolean which indicates if this is a resized image.
Note that it is possible for more than one yield to result from this
check.
If no base file is found, then nothing is yielded.
"""
# The original file from glance
base_file = os.path.join(base_dir, fingerprint)
if os.path.exists(base_file):
yield base_file, False, False
# An older naming style which can be removed sometime after Folsom
base_file = os.path.join(base_dir, fingerprint + '_sm')
if os.path.exists(base_file):
yield base_file, True, False
# Resized images
resize_re = re.compile('.*/%s_[0-9]+$' % fingerprint)
for img in self.unexplained_images:
m = resize_re.match(img)
if m:
yield img, False, True
def _verify_checksum(self, img_id, base_file, create_if_missing=True):
"""Compare the checksum stored on disk with the current file.
Note that if the checksum fails to verify this is logged, but no actual
action occurs. This is something sysadmins should monitor for and
handle manually when it occurs.
"""
if not CONF.libvirt.checksum_base_images:
return None
lock_name = 'hash-%s' % os.path.split(base_file)[-1]
# Protect against other nova-computes performing checksums at the same
# time if we are using shared storage
@utils.synchronized(lock_name, external=True, lock_path=self.lock_path)
def inner_verify_checksum():
(stored_checksum, stored_timestamp) = read_stored_checksum(
base_file, timestamped=True)
if stored_checksum:
# NOTE(mikal): Checksums are timestamped. If we have recently
# checksummed (possibly on another compute node if we are using
# shared storage), then we don't need to checksum again.
if (stored_timestamp and
time.time() - stored_timestamp <
CONF.libvirt.checksum_interval_seconds):
return True
# NOTE(mikal): If there is no timestamp, then the checksum was
# performed by a previous version of the code.
if not stored_timestamp:
write_stored_info(base_file, field='sha1',
value=stored_checksum)
current_checksum = _hash_file(base_file)
if current_checksum != stored_checksum:
LOG.error(_LE('image %(id)s at (%(base_file)s): image '
'verification failed'),
{'id': img_id,
'base_file': base_file})
return False
else:
return True
else:
LOG.info(_LI('image %(id)s at (%(base_file)s): image '
'verification skipped, no hash stored'),
{'id': img_id,
'base_file': base_file})
# NOTE(mikal): If the checksum file is missing, then we should
# create one. We don't create checksums when we download images
# from glance because that would delay VM startup.
if CONF.libvirt.checksum_base_images and create_if_missing:
LOG.info(_LI('%(id)s (%(base_file)s): generating '
'checksum'),
{'id': img_id,
'base_file': base_file})
write_stored_checksum(base_file)
return None
return inner_verify_checksum()
@staticmethod
def _get_age_of_file(base_file):
if not os.path.exists(base_file):
LOG.debug('Cannot remove %s, it does not exist', base_file)
return (False, 0)
mtime = os.path.getmtime(base_file)
age = time.time() - mtime
return (True, age)
def _remove_old_enough_file(self, base_file, maxage, remove_sig=True,
remove_lock=True):
"""Remove a single swap or base file if it is old enough."""
exists, age = self._get_age_of_file(base_file)
if not exists:
return
lock_file = os.path.split(base_file)[-1]
@utils.synchronized(lock_file, external=True,
lock_path=self.lock_path)
def _inner_remove_old_enough_file():
# NOTE(mikal): recheck that the file is old enough, as a new
# user of the file might have come along while we were waiting
# for the lock
exists, age = self._get_age_of_file(base_file)
if not exists or age < maxage:
return
LOG.info(_LI('Removing base or swap file: %s'), base_file)
try:
os.remove(base_file)
if remove_sig:
signature = get_info_filename(base_file)
if os.path.exists(signature):
os.remove(signature)
except OSError as e:
LOG.error(_LE('Failed to remove %(base_file)s, '
'error was %(error)s'),
{'base_file': base_file,
'error': e})
if age < maxage:
LOG.info(_LI('Base or swap file too young to remove: %s'),
base_file)
else:
_inner_remove_old_enough_file()
if remove_lock:
try:
# NOTE(jichenjc) The lock file will be constructed first
# time the image file was accessed. the lock file looks
# like nova-9e881789030568a317fad9daae82c5b1c65e0d4a
# or nova-03d8e206-6500-4d91-b47d-ee74897f9b4e
# according to the original file name
lockutils.remove_external_lock_file(lock_file,
lock_file_prefix='nova-', lock_path=self.lock_path)
except OSError as e:
LOG.debug('Failed to remove %(lock_file)s, '
'error was %(error)s',
{'lock_file': lock_file,
'error': e})
def _remove_swap_file(self, base_file):
"""Remove a single swap base file if it is old enough."""
maxage = CONF.remove_unused_original_minimum_age_seconds
self._remove_old_enough_file(base_file, maxage, remove_sig=False,
remove_lock=False)
def _remove_base_file(self, base_file):
"""Remove a single base file if it is old enough."""
maxage = CONF.libvirt.remove_unused_resized_minimum_age_seconds
if base_file in self.originals:
maxage = CONF.remove_unused_original_minimum_age_seconds
self._remove_old_enough_file(base_file, maxage)
def _handle_base_image(self, img_id, base_file):
"""Handle the checks for a single base image."""
image_bad = False
image_in_use = False
LOG.info(_LI('image %(id)s at (%(base_file)s): checking'),
{'id': img_id,
'base_file': base_file})
if base_file in self.unexplained_images:
self.unexplained_images.remove(base_file)
if (base_file and os.path.exists(base_file)
and os.path.isfile(base_file)):
# _verify_checksum returns True if the checksum is ok, and None if
# there is no checksum file
checksum_result = self._verify_checksum(img_id, base_file)
if checksum_result is not None:
image_bad = not checksum_result
# Give other threads a chance to run
time.sleep(0)
if img_id in self.used_images:
local, remote, instances = self.used_images[img_id]
if local > 0 or remote > 0:
image_in_use = True
LOG.info(_LI('image %(id)s at (%(base_file)s): '
'in use: on this node %(local)d local, '
'%(remote)d on other nodes sharing this instance '
'storage'),
{'id': img_id,
'base_file': base_file,
'local': local,
'remote': remote})
self.active_base_files.append(base_file)
if not base_file:
LOG.warning(_LW('image %(id)s at (%(base_file)s): warning '
'-- an absent base file is in use! '
'instances: %(instance_list)s'),
{'id': img_id,
'base_file': base_file,
'instance_list': ' '.join(instances)})
if image_bad:
self.corrupt_base_files.append(base_file)
if base_file:
if not image_in_use:
LOG.debug('image %(id)s at (%(base_file)s): image is not in '
'use',
{'id': img_id,
'base_file': base_file})
self.removable_base_files.append(base_file)
else:
LOG.debug('image %(id)s at (%(base_file)s): image is in '
'use',
{'id': img_id,
'base_file': base_file})
if os.path.exists(base_file):
libvirt_utils.update_mtime(base_file)
def _age_and_verify_swap_images(self, context, base_dir):
LOG.debug('Verify swap images')
for ent in self.back_swap_images:
base_file = os.path.join(base_dir, ent)
if ent in self.used_swap_images and os.path.exists(base_file):
libvirt_utils.update_mtime(base_file)
elif self.remove_unused_base_images:
self._remove_swap_file(base_file)
error_images = self.used_swap_images - self.back_swap_images
for error_image in error_images:
LOG.warning(_LW('%s swap image was used by instance'
' but no back files existing!'), error_image)
def _age_and_verify_cached_images(self, context, all_instances, base_dir):
LOG.debug('Verify base images')
# Determine what images are on disk because they're in use
for img in self.used_images:
fingerprint = hashlib.sha1(img).hexdigest()
LOG.debug('Image id %(id)s yields fingerprint %(fingerprint)s',
{'id': img,
'fingerprint': fingerprint})
for result in self._find_base_file(base_dir, fingerprint):
base_file, image_small, image_resized = result
self._handle_base_image(img, base_file)
if not image_small and not image_resized:
self.originals.append(base_file)
# Elements remaining in unexplained_images might be in use
inuse_backing_images = self._list_backing_images()
for backing_path in inuse_backing_images:
if backing_path not in self.active_base_files:
self.active_base_files.append(backing_path)
# Anything left is an unknown base image
for img in self.unexplained_images:
LOG.warning(_LW('Unknown base file: %s'), img)
self.removable_base_files.append(img)
# Dump these lists
if self.active_base_files:
LOG.info(_LI('Active base files: %s'),
' '.join(self.active_base_files))
if self.corrupt_base_files:
LOG.info(_LI('Corrupt base files: %s'),
' '.join(self.corrupt_base_files))
if self.removable_base_files:
LOG.info(_LI('Removable base files: %s'),
' '.join(self.removable_base_files))
if self.remove_unused_base_images:
for base_file in self.removable_base_files:
self._remove_base_file(base_file)
# That's it
LOG.debug('Verification complete')
def _get_base(self):
# NOTE(mikal): The new scheme for base images is as follows -- an
# image is streamed from the image service to _base (filename is the
# sha1 hash of the image id). If CoW is enabled, that file is then
# resized to be the correct size for the instance (filename is the
# same as the original, but with an underscore and the resized size
# in bytes). This second file is then CoW'd to the instance disk. If
# CoW is disabled, the resize occurs as part of the copy from the
# cache to the instance directory. Files ending in _sm are no longer
# created, but may remain from previous versions.
base_dir = os.path.join(CONF.instances_path,
CONF.image_cache_subdirectory_name)
if not os.path.exists(base_dir):
LOG.debug('Skipping verification, no base directory at %s',
base_dir)
return
return base_dir
def update(self, context, all_instances):
base_dir = self._get_base()
if not base_dir:
return
# reset the local statistics
self._reset_state()
# read the cached images
self._list_base_images(base_dir)
# read running instances data
running = self._list_running_instances(context, all_instances)
self.used_images = running['used_images']
self.image_popularity = running['image_popularity']
self.instance_names = running['instance_names']
self.used_swap_images = running['used_swap_images']
# perform the aging and image verification
self._age_and_verify_cached_images(context, all_instances, base_dir)
self._age_and_verify_swap_images(context, base_dir)
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