/usr/lib/python2.7/dist-packages/larch/journal.py is in python-larch 1.20151025-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 | # Copyright 2012 Lars Wirzenius
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import errno
import logging
import os
import tracing
import larch
class ReadOnlyMode(larch.Error): # pragma: no cover
def __init__(self):
self.msg = 'Larch B-tree is in read-only mode, no changes allowed'
class Journal(object):
'''A journal layer on top of a virtual filesystem.
The journal solves the problem of updating on-disk data structures
atomically. Changes are first written to a journal, and then moved
from there to the real location. If the program or system crashes,
the changes can be completed later on, or rolled back, depending
on what's needed for consistency.
The journal works as follows:
* ``x`` is the real filename
* ``new/x`` is a new or modified file
* ``delete/x`` is a deleted file, created there as a flag file
Commit does this:
* for every ``delete/x``, remove ``x``
* for every ``new/x`` except ``new/metadata``, move to ``x``
* move ``new/metadata`` to ``metadata``
Rollback does this:
* remove every ``new/x``
* remove every ``delete/x``
When a journalled node store is opened, if ``new/metadata`` exists,
the commit happens. Otherwise a rollback happens. This guarantees
that the on-disk state is consistent.
We only provide enough of a filesystem interface as is needed by
NodeStoreDisk. For example, we do not care about directory removal.
The journal can be opened in read-only mode, in which case it ignores
any changes in ``new`` and ``delete``, and does not try to rollback or
commit at start.
'''
flag_basename = 'metadata'
def __init__(self, allow_writes, fs, storedir):
logging.debug('Initializing Journal for %s' % storedir)
self.allow_writes = allow_writes
self.fs = fs
self.storedir = storedir
if not self.storedir.endswith(os.sep):
self.storedir += os.sep
self.newdir = os.path.join(self.storedir, 'new/')
self.deletedir = os.path.join(self.storedir, 'delete/')
self.flag_file = os.path.join(self.storedir, self.flag_basename)
self.new_flag = os.path.join(self.newdir, self.flag_basename)
self.new_flag_seen = self.fs.exists(self.new_flag)
tracing.trace('self.new_flag_seen: %s' % self.new_flag_seen)
if self.allow_writes:
if self.new_flag_seen:
logging.debug('Automatically committing remaining changes')
self.commit()
else:
logging.debug('Automatically rolling back remaining changes')
self.rollback()
else:
logging.debug('Not committing/rolling back since read-only')
self.new_files = set()
self.deleted_files = set()
def _require_rw(self):
'''Raise error if modifications are not allowed.'''
if not self.allow_writes:
raise ReadOnlyMode()
def _relative(self, filename):
'''Return the part of filename that is relative to storedir.'''
assert filename.startswith(self.storedir)
return filename[len(self.storedir):]
def _new(self, filename):
'''Return name for a new file whose final name is filename.'''
return os.path.join(self.newdir, self._relative(filename))
def _deleted(self, filename):
'''Return name for temporary name for file to be deleted.'''
return os.path.join(self.deletedir, self._relative(filename))
def _realname(self, journaldir, filename):
'''Return real name for a file in a journal temporary directory.'''
assert filename.startswith(journaldir)
return os.path.join(self.storedir, filename[len(journaldir):])
def _is_in_new(self, filename):
new = self._new(filename)
return new in self.new_files or self.fs.exists(new)
def _is_in_deleted(self, filename):
deleted = self._deleted(filename)
return deleted in self.deleted_files or self.fs.exists(deleted)
def exists(self, filename):
if self.allow_writes or self.new_flag_seen:
if self._is_in_new(filename):
return True
elif self._is_in_deleted(filename):
return False
return self.fs.exists(filename)
def makedirs(self, dirname):
tracing.trace(dirname)
self._require_rw()
x = self._new(dirname)
self.fs.makedirs(x)
self.new_files.add(x)
def overwrite_file(self, filename, contents):
tracing.trace(filename)
self._require_rw()
new = self._new(filename)
self.fs.overwrite_file(new, contents)
self.new_files.add(new)
def cat(self, filename):
tracing.trace('filename=%s' % filename)
tracing.trace('allow_writes=%s' % self.allow_writes)
tracing.trace('new_flag_seen=%s' % self.new_flag_seen)
if self.allow_writes or self.new_flag_seen:
if self._is_in_new(filename):
return self.fs.cat(self._new(filename))
elif self._is_in_deleted(filename):
raise OSError(
errno.ENOENT, os.strerror(errno.ENOENT), filename)
return self.fs.cat(filename)
def remove(self, filename):
tracing.trace(filename)
self._require_rw()
new = self._new(filename)
deleted = self._deleted(filename)
if new in self.new_files:
self.fs.remove(new)
self.new_files.remove(new)
elif deleted in self.deleted_files:
raise OSError(errno.ENOENT, os.strerror(errno.ENOENT), filename)
else:
self.fs.overwrite_file(deleted, '')
self.deleted_files.add(deleted)
def list_files(self, dirname):
'''List all files.
Files only, no directories.
'''
assert not dirname.startswith(self.newdir)
assert not dirname.startswith(self.deletedir)
if self.allow_writes or self.new_flag_seen:
if self.fs.exists(dirname):
for x in self.climb(dirname, files_only=True):
if self.exists(x):
yield x
new = self._new(dirname)
if self.fs.exists(new):
for x in self.climb(new, files_only=True):
yield self._realname(self.newdir, x)
else:
if self.fs.exists(dirname):
for x in self.climb(dirname, files_only=True):
in_new = x.startswith(self.newdir)
in_deleted = x.startswith(self.deletedir)
if not in_new and not in_deleted:
yield x
def climb(self, dirname, files_only=False):
basenames = self.fs.listdir(dirname)
filenames = []
for basename in basenames:
pathname = os.path.join(dirname, basename)
if self.fs.isdir(pathname):
for x in self.climb(pathname, files_only=files_only):
yield x
else:
filenames.append(pathname)
for filename in filenames:
yield filename
if not files_only:
yield dirname
def _clear_directory(self, dirname):
tracing.trace(dirname)
for pathname in self.climb(dirname):
if pathname != dirname:
if self.fs.isdir(pathname):
self.fs.rmdir(pathname)
else:
self.fs.remove(pathname)
def _vivify(self, dirname, exclude):
tracing.trace('dirname: %s' % dirname)
tracing.trace('exclude: %s' % repr(exclude))
all_excludes = [dirname] + exclude
for pathname in self.climb(dirname):
if pathname not in all_excludes:
r = self._realname(dirname, pathname)
parent = os.path.dirname(r)
if self.fs.isdir(pathname):
if not self.fs.exists(r):
if not self.fs.exists(parent):
self.fs.makedirs(parent)
self.fs.rename(pathname, r)
else:
if not self.fs.exists(parent):
self.fs.makedirs(parent)
self.fs.rename(pathname, r)
def rollback(self):
tracing.trace('%s start' % self.storedir)
self._require_rw()
if self.fs.exists(self.newdir):
self._clear_directory(self.newdir)
if self.fs.exists(self.deletedir):
self._clear_directory(self.deletedir)
self.new_files = set()
self.deleted_files = set()
tracing.trace('%s done' % self.storedir)
def _really_delete(self, deletedir):
tracing.trace(deletedir)
for pathname in self.climb(deletedir, files_only=True):
if pathname != deletedir:
realname = self._realname(deletedir, pathname)
try:
self.fs.remove(realname)
except OSError, e: # pragma: no cover
if e.errno not in (errno.ENOENT, errno.EISDIR):
raise
self.fs.remove(pathname)
def commit(self, skip=[]):
tracing.trace('%s start' % self.storedir)
self._require_rw()
if self.fs.exists(self.deletedir):
self._really_delete(self.deletedir)
if self.fs.exists(self.newdir):
skip = [self._new(x) for x in skip]
self._vivify(self.newdir, [self.new_flag] + skip)
if not skip and self.fs.exists(self.new_flag):
self.fs.rename(self.new_flag, self.flag_file)
self.new_files = set()
self.deleted_files = set()
tracing.trace('%s done' % self.storedir)
|