/usr/lib/python3/dist-packages/bmaptools/Filemap.py is in bmap-tools 3.4-1.
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 | # -*- coding: utf-8 -*-
# vim: ts=4 sw=4 et ai si
#
# Copyright (c) 2012-2014 Intel, Inc.
# License: GPLv2
# Author: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License, version 2,
# as published by the Free Software Foundation.
#
# 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.
"""
This module implements python implements a way to get file block. Two methods
are supported - the FIEMAP ioctl and the 'SEEK_HOLE / SEEK_DATA' features of
the file seek syscall. The former is implemented by the 'FilemapFiemap' class,
the latter is implemented by the 'FilemapSeek' class. Both classes provide the
same API. The 'filemap' function automatically selects which class can be used
and returns an instance of the class.
"""
# Disable the following pylint recommendations:
# * Too many instance attributes (R0902)
# pylint: disable=R0902
import os
import errno
import struct
import array
import fcntl
import tempfile
import logging
from bmaptools import BmapHelpers
_log = logging.getLogger(__name__) # pylint: disable=C0103
class ErrorNotSupp(Exception):
"""
An exception of this type is raised when the 'FIEMAP' or 'SEEK_HOLE' feature
is not supported either by the kernel or the file-system.
"""
pass
class Error(Exception):
"""A class for all the other exceptions raised by this module."""
pass
class _FilemapBase(object):
"""
This is a base class for a couple of other classes in this module. This
class simply performs the common parts of the initialization process: opens
the image file, gets its size, etc.
"""
def __init__(self, image):
"""
Initialize a class instance. The 'image' argument is full path to the
file or file object to operate on.
"""
self._f_image_needs_close = False
if hasattr(image, "fileno"):
self._f_image = image
self._image_path = image.name
else:
self._image_path = image
self._open_image_file()
try:
self.image_size = os.fstat(self._f_image.fileno()).st_size
except IOError as err:
raise Error("cannot get information about file '%s': %s"
% (self._f_image.name, err))
try:
self.block_size = BmapHelpers.get_block_size(self._f_image)
except IOError as err:
raise Error("cannot get block size for '%s': %s"
% (self._image_path, err))
self.blocks_cnt = (self.image_size + self.block_size - 1) // self.block_size
try:
self._f_image.flush()
except IOError as err:
raise Error("cannot flush image file '%s': %s"
% (self._image_path, err))
try:
os.fsync(self._f_image.fileno()),
except OSError as err:
raise Error("cannot synchronize image file '%s': %s "
% (self._image_path, err.strerror))
_log.debug("opened image \"%s\"" % self._image_path)
_log.debug("block size %d, blocks count %d, image size %d"
% (self.block_size, self.blocks_cnt, self.image_size))
def __del__(self):
"""The class destructor which just closes the image file."""
if self._f_image_needs_close:
self._f_image.close()
def _open_image_file(self):
"""Open the image file."""
try:
self._f_image = open(self._image_path, 'rb')
except IOError as err:
raise Error("cannot open image file '%s': %s"
% (self._image_path, err))
self._f_image_needs_close = True
def block_is_mapped(self, block): # pylint: disable=W0613,R0201
"""
This method has has to be implemented by child classes. It returns
'True' if block number 'block' of the image file is mapped and 'False'
otherwise.
"""
raise Error("the method is not implemented")
def block_is_unmapped(self, block): # pylint: disable=W0613,R0201
"""
This method has has to be implemented by child classes. It returns
'True' if block number 'block' of the image file is not mapped (hole)
and 'False' otherwise.
"""
raise Error("the method is not implemented")
def get_mapped_ranges(self, start, count): # pylint: disable=W0613,R0201
"""
This method has has to be implemented by child classes. This is a
generator which yields ranges of mapped blocks in the file. The ranges
are tuples of 2 elements: [first, last], where 'first' is the first
mapped block and 'last' is the last mapped block.
The ranges are yielded for the area of the file of size 'count' blocks,
starting from block 'start'.
"""
raise Error("the method is not implemented")
def get_unmapped_ranges(self, start, count): # pylint: disable=W0613,R0201
"""
This method has has to be implemented by child classes. Just like
'get_mapped_ranges()', but yields unmapped block ranges instead
(holes).
"""
raise Error("the method is not implemented")
# The 'SEEK_HOLE' and 'SEEK_DATA' options of the file seek system call
_SEEK_DATA = 3
_SEEK_HOLE = 4
def _lseek(file_obj, offset, whence):
"""This is a helper function which invokes 'os.lseek' for file object
'file_obj' and with specified 'offset' and 'whence'. The 'whence'
argument is supposed to be either '_SEEK_DATA' or '_SEEK_HOLE'. When
there is no more data or hole starting from 'offset', this function
returns '-1'. Otherwise the data or hole position is returned."""
try:
return os.lseek(file_obj.fileno(), offset, whence)
except OSError as err:
# The 'lseek' system call returns the ENXIO if there is no data or
# hole starting from the specified offset.
if err.errno == errno.ENXIO:
return -1
elif err.errno == errno.EINVAL:
raise ErrorNotSupp("the kernel or file-system does not support "
"\"SEEK_HOLE\" and \"SEEK_DATA\"")
else:
raise
class FilemapSeek(_FilemapBase):
"""
This class uses the 'SEEK_HOLE' and 'SEEK_DATA' to find file block mapping.
Unfortunately, the current implementation requires the caller to have write
access to the image file.
"""
def __init__(self, image):
"""Refer the '_FilemapBase' class for the documentation."""
# Call the base class constructor first
_FilemapBase.__init__(self, image)
_log.debug("FilemapSeek: initializing")
self._probe_seek_hole()
def _probe_seek_hole(self):
"""
Check whether the system implements 'SEEK_HOLE' and 'SEEK_DATA'.
Unfortunately, there seems to be no clean way for detecting this,
because often the system just fakes them by just assuming that all
files are fully mapped, so 'SEEK_HOLE' always returns EOF and
'SEEK_DATA' always returns the requested offset.
I could not invent a better way of detecting the fake 'SEEK_HOLE'
implementation than just to create a temporary file in the same
directory where the image file resides. It would be nice to change this
to something better.
"""
directory = os.path.dirname(self._image_path)
try:
tmp_obj = tempfile.TemporaryFile("w+", dir=directory)
except IOError as err:
raise ErrorNotSupp("cannot create a temporary in \"%s\": %s"
% (directory, err))
try:
os.ftruncate(tmp_obj.fileno(), self.block_size)
except OSError as err:
raise ErrorNotSupp("cannot truncate temporary file in \"%s\": %s"
% (directory, err))
offs = _lseek(tmp_obj, 0, _SEEK_HOLE)
if offs != 0:
# We are dealing with the stub 'SEEK_HOLE' implementation which
# always returns EOF.
_log.debug("lseek(0, SEEK_HOLE) returned %d" % offs)
raise ErrorNotSupp("the file-system does not support "
"\"SEEK_HOLE\" and \"SEEK_DATA\" but only "
"provides a stub implementation")
tmp_obj.close()
def block_is_mapped(self, block):
"""Refer the '_FilemapBase' class for the documentation."""
offs = _lseek(self._f_image, block * self.block_size, _SEEK_DATA)
if offs == -1:
result = False
else:
result = (offs // self.block_size == block)
_log.debug("FilemapSeek: block_is_mapped(%d) returns %s"
% (block, result))
return result
def block_is_unmapped(self, block):
"""Refer the '_FilemapBase' class for the documentation."""
return not self.block_is_mapped(block)
def _get_ranges(self, start, count, whence1, whence2):
"""
This function implements 'get_mapped_ranges()' and
'get_unmapped_ranges()' depending on what is passed in the 'whence1'
and 'whence2' arguments.
"""
assert whence1 != whence2
end = start * self.block_size
limit = end + count * self.block_size
while True:
start = _lseek(self._f_image, end, whence1)
if start == -1 or start >= limit or start == self.image_size:
break
end = _lseek(self._f_image, start, whence2)
if end == -1 or end == self.image_size:
end = self.blocks_cnt * self.block_size
if end > limit:
end = limit
start_blk = start // self.block_size
end_blk = end // self.block_size - 1
_log.debug("FilemapSeek: yielding range (%d, %d)"
% (start_blk, end_blk))
yield (start_blk, end_blk)
def get_mapped_ranges(self, start, count):
"""Refer the '_FilemapBase' class for the documentation."""
_log.debug("FilemapSeek: get_mapped_ranges(%d, %d(%d))"
% (start, count, start + count - 1))
return self._get_ranges(start, count, _SEEK_DATA, _SEEK_HOLE)
def get_unmapped_ranges(self, start, count):
"""Refer the '_FilemapBase' class for the documentation."""
_log.debug("FilemapSeek: get_unmapped_ranges(%d, %d(%d))"
% (start, count, start + count - 1))
return self._get_ranges(start, count, _SEEK_HOLE, _SEEK_DATA)
# Below goes the FIEMAP ioctl implementation, which is not very readable
# because it deals with the rather complex FIEMAP ioctl. To understand the
# code, you need to know the FIEMAP interface, which is documented in the
# "Documentation/filesystems/fiemap.txt" file in the Linux kernel sources.
# Format string for 'struct fiemap'
_FIEMAP_FORMAT = "=QQLLLL"
# sizeof(struct fiemap)
_FIEMAP_SIZE = struct.calcsize(_FIEMAP_FORMAT)
# Format string for 'struct fiemap_extent'
_FIEMAP_EXTENT_FORMAT = "=QQQQQLLLL"
# sizeof(struct fiemap_extent)
_FIEMAP_EXTENT_SIZE = struct.calcsize(_FIEMAP_EXTENT_FORMAT)
# The FIEMAP ioctl number
_FIEMAP_IOCTL = 0xC020660B
# This FIEMAP ioctl flag which instructs the kernel to sync the file before
# reading the block map
_FIEMAP_FLAG_SYNC = 0x00000001
# Size of the buffer for 'struct fiemap_extent' elements which will be used
# when invoking the FIEMAP ioctl. The larger is the buffer, the less times the
# FIEMAP ioctl will be invoked.
_FIEMAP_BUFFER_SIZE = 256 * 1024
class FilemapFiemap(_FilemapBase):
"""
This class provides API to the FIEMAP ioctl. Namely, it allows to iterate
over all mapped blocks and over all holes.
This class synchronizes the image file every time it invokes the FIEMAP
ioctl in order to work-around early FIEMAP implementation kernel bugs.
"""
def __init__(self, image):
"""
Initialize a class instance. The 'image' argument is full the file
object to operate on.
"""
# Call the base class constructor first
_FilemapBase.__init__(self, image)
_log.debug("FilemapFiemap: initializing")
self._buf_size = _FIEMAP_BUFFER_SIZE
# Calculate how many 'struct fiemap_extent' elements fit the buffer
self._buf_size -= _FIEMAP_SIZE
self._fiemap_extent_cnt = self._buf_size // _FIEMAP_EXTENT_SIZE
assert self._fiemap_extent_cnt > 0
self._buf_size = self._fiemap_extent_cnt * _FIEMAP_EXTENT_SIZE
self._buf_size += _FIEMAP_SIZE
# Allocate a mutable buffer for the FIEMAP ioctl
self._buf = array.array('B', [0] * self._buf_size)
# Check if the FIEMAP ioctl is supported
self.block_is_mapped(0)
def _invoke_fiemap(self, block, count):
"""
Invoke the FIEMAP ioctl for 'count' blocks of the file starting from
block number 'block'.
The full result of the operation is stored in 'self._buf' on exit.
Returns the unpacked 'struct fiemap' data structure in form of a python
list (just like 'struct.upack()').
"""
if self.blocks_cnt != 0 and (block < 0 or block >= self.blocks_cnt):
raise Error("bad block number %d, should be within [0, %d]"
% (block, self.blocks_cnt))
# Initialize the 'struct fiemap' part of the buffer. We use the
# '_FIEMAP_FLAG_SYNC' flag in order to make sure the file is
# synchronized. The reason for this is that early FIEMAP
# implementations had many bugs related to cached dirty data, and
# synchronizing the file is a necessary work-around.
struct.pack_into(_FIEMAP_FORMAT, self._buf, 0, block * self.block_size,
count * self.block_size, _FIEMAP_FLAG_SYNC, 0,
self._fiemap_extent_cnt, 0)
try:
fcntl.ioctl(self._f_image, _FIEMAP_IOCTL, self._buf, 1)
except IOError as err:
# Note, the FIEMAP ioctl is supported by the Linux kernel starting
# from version 2.6.28 (year 2008).
if err.errno == errno.EOPNOTSUPP:
errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
"by the file-system"
_log.debug(errstr)
raise ErrorNotSupp(errstr)
if err.errno == errno.ENOTTY:
errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
"by the kernel"
_log.debug(errstr)
raise ErrorNotSupp(errstr)
raise Error("the FIEMAP ioctl failed for '%s': %s"
% (self._image_path, err))
return struct.unpack(_FIEMAP_FORMAT, self._buf[:_FIEMAP_SIZE])
def block_is_mapped(self, block):
"""Refer the '_FilemapBase' class for the documentation."""
struct_fiemap = self._invoke_fiemap(block, 1)
# The 3rd element of 'struct_fiemap' is the 'fm_mapped_extents' field.
# If it contains zero, the block is not mapped, otherwise it is
# mapped.
result = bool(struct_fiemap[3])
_log.debug("FilemapFiemap: block_is_mapped(%d) returns %s"
% (block, result))
return result
def block_is_unmapped(self, block):
"""Refer the '_FilemapBase' class for the documentation."""
return not self.block_is_mapped(block)
def _unpack_fiemap_extent(self, index):
"""
Unpack a 'struct fiemap_extent' structure object number 'index' from
the internal 'self._buf' buffer.
"""
offset = _FIEMAP_SIZE + _FIEMAP_EXTENT_SIZE * index
return struct.unpack(_FIEMAP_EXTENT_FORMAT,
self._buf[offset: offset + _FIEMAP_EXTENT_SIZE])
def _do_get_mapped_ranges(self, start, count):
"""
Implements most the functionality for the 'get_mapped_ranges()'
generator: invokes the FIEMAP ioctl, walks through the mapped extents
and yields mapped block ranges. However, the ranges may be consecutive
(e.g., (1, 100), (100, 200)) and 'get_mapped_ranges()' simply merges
them.
"""
block = start
while block < start + count:
struct_fiemap = self._invoke_fiemap(block, count)
mapped_extents = struct_fiemap[3]
if mapped_extents == 0:
# No more mapped blocks
return
extent = 0
while extent < mapped_extents:
fiemap_extent = self._unpack_fiemap_extent(extent)
# Start of the extent
extent_start = fiemap_extent[0]
# Starting block number of the extent
extent_block = extent_start // self.block_size
# Length of the extent
extent_len = fiemap_extent[2]
# Count of blocks in the extent
extent_count = extent_len // self.block_size
# Extent length and offset have to be block-aligned
assert extent_start % self.block_size == 0
assert extent_len % self.block_size == 0
if extent_block > start + count - 1:
return
first = max(extent_block, block)
last = min(extent_block + extent_count, start + count) - 1
yield (first, last)
extent += 1
block = extent_block + extent_count
def get_mapped_ranges(self, start, count):
"""Refer the '_FilemapBase' class for the documentation."""
_log.debug("FilemapFiemap: get_mapped_ranges(%d, %d(%d))"
% (start, count, start + count - 1))
iterator = self._do_get_mapped_ranges(start, count)
first_prev, last_prev = next(iterator)
for first, last in iterator:
if last_prev == first - 1:
last_prev = last
else:
_log.debug("FilemapFiemap: yielding range (%d, %d)"
% (first_prev, last_prev))
yield (first_prev, last_prev)
first_prev, last_prev = first, last
_log.debug("FilemapFiemap: yielding range (%d, %d)"
% (first_prev, last_prev))
yield (first_prev, last_prev)
def get_unmapped_ranges(self, start, count):
"""Refer the '_FilemapBase' class for the documentation."""
_log.debug("FilemapFiemap: get_unmapped_ranges(%d, %d(%d))"
% (start, count, start + count - 1))
hole_first = start
for first, last in self._do_get_mapped_ranges(start, count):
if first > hole_first:
_log.debug("FilemapFiemap: yielding range (%d, %d)"
% (hole_first, first - 1))
yield (hole_first, first - 1)
hole_first = last + 1
if hole_first < start + count:
_log.debug("FilemapFiemap: yielding range (%d, %d)"
% (hole_first, start + count - 1))
yield (hole_first, start + count - 1)
def filemap(image):
"""
Create and return an instance of a Filemap class - 'FilemapFiemap' or
'FilemapSeek', depending on what the system we run on supports. If the
FIEMAP ioctl is supported, an instance of the 'FilemapFiemap' class is
returned. Otherwise, if 'SEEK_HOLE' is supported an instance of the
'FilemapSeek' class is returned. If none of these are supported, the
function generates an 'Error' type exception.
"""
try:
return FilemapFiemap(image)
except ErrorNotSupp:
return FilemapSeek(image)
|