593 lines
22 KiB
Python
593 lines
22 KiB
Python
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# Copyright (c) 2012 Intel, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License, version 2,
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# as published by the Free Software Foundation.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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"""
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This module implements python implements a way to get file block. Two methods
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are supported - the FIEMAP ioctl and the 'SEEK_HOLE / SEEK_DATA' features of
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the file seek syscall. The former is implemented by the 'FilemapFiemap' class,
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the latter is implemented by the 'FilemapSeek' class. Both classes provide the
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same API. The 'filemap' function automatically selects which class can be used
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and returns an instance of the class.
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"""
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# Disable the following pylint recommendations:
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# * Too many instance attributes (R0902)
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# pylint: disable=R0902
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import os
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import struct
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import array
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import fcntl
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import tempfile
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import logging
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def get_block_size(file_obj):
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"""
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Returns block size for file object 'file_obj'. Errors are indicated by the
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'IOError' exception.
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"""
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# Get the block size of the host file-system for the image file by calling
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# the FIGETBSZ ioctl (number 2).
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binary_data = fcntl.ioctl(file_obj, 2, struct.pack('I', 0))
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return struct.unpack('I', binary_data)[0]
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class ErrorNotSupp(Exception):
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"""
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An exception of this type is raised when the 'FIEMAP' or 'SEEK_HOLE' feature
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is not supported either by the kernel or the file-system.
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"""
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pass
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class Error(Exception):
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"""A class for all the other exceptions raised by this module."""
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pass
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class _FilemapBase(object):
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"""
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This is a base class for a couple of other classes in this module. This
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class simply performs the common parts of the initialization process: opens
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the image file, gets its size, etc. The 'log' parameter is the logger object
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to use for printing messages.
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"""
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def __init__(self, image, log=None):
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"""
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Initialize a class instance. The 'image' argument is full path to the
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file or file object to operate on.
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"""
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self._log = log
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if self._log is None:
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self._log = logging.getLogger(__name__)
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self._f_image_needs_close = False
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if hasattr(image, "fileno"):
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self._f_image = image
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self._image_path = image.name
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else:
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self._image_path = image
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self._open_image_file()
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try:
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self.image_size = os.fstat(self._f_image.fileno()).st_size
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except IOError as err:
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raise Error("cannot get information about file '%s': %s"
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% (self._f_image.name, err))
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try:
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self.block_size = get_block_size(self._f_image)
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except IOError as err:
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raise Error("cannot get block size for '%s': %s"
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% (self._image_path, err))
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self.blocks_cnt = self.image_size + self.block_size - 1
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self.blocks_cnt //= self.block_size
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try:
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self._f_image.flush()
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except IOError as err:
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raise Error("cannot flush image file '%s': %s"
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% (self._image_path, err))
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try:
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os.fsync(self._f_image.fileno()),
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except OSError as err:
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raise Error("cannot synchronize image file '%s': %s "
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% (self._image_path, err.strerror))
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self._log.debug("opened image \"%s\"" % self._image_path)
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self._log.debug("block size %d, blocks count %d, image size %d"
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% (self.block_size, self.blocks_cnt, self.image_size))
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def __del__(self):
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"""The class destructor which just closes the image file."""
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if self._f_image_needs_close:
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self._f_image.close()
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def _open_image_file(self):
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"""Open the image file."""
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try:
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self._f_image = open(self._image_path, 'rb')
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except IOError as err:
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raise Error("cannot open image file '%s': %s"
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% (self._image_path, err))
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self._f_image_needs_close = True
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def block_is_mapped(self, block): # pylint: disable=W0613,R0201
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"""
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This method has has to be implemented by child classes. It returns
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'True' if block number 'block' of the image file is mapped and 'False'
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otherwise.
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"""
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raise Error("the method is not implemented")
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def block_is_unmapped(self, block): # pylint: disable=W0613,R0201
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"""
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This method has has to be implemented by child classes. It returns
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'True' if block number 'block' of the image file is not mapped (hole)
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and 'False' otherwise.
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"""
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raise Error("the method is not implemented")
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def get_mapped_ranges(self, start, count): # pylint: disable=W0613,R0201
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"""
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This method has has to be implemented by child classes. This is a
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generator which yields ranges of mapped blocks in the file. The ranges
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are tuples of 2 elements: [first, last], where 'first' is the first
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mapped block and 'last' is the last mapped block.
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The ranges are yielded for the area of the file of size 'count' blocks,
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starting from block 'start'.
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"""
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raise Error("the method is not implemented")
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def get_unmapped_ranges(self, start, count): # pylint: disable=W0613,R0201
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"""
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This method has has to be implemented by child classes. Just like
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'get_mapped_ranges()', but yields unmapped block ranges instead
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(holes).
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"""
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raise Error("the method is not implemented")
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# The 'SEEK_HOLE' and 'SEEK_DATA' options of the file seek system call
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_SEEK_DATA = 3
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_SEEK_HOLE = 4
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def _lseek(file_obj, offset, whence):
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"""This is a helper function which invokes 'os.lseek' for file object
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'file_obj' and with specified 'offset' and 'whence'. The 'whence'
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argument is supposed to be either '_SEEK_DATA' or '_SEEK_HOLE'. When
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there is no more data or hole starting from 'offset', this function
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returns '-1'. Otherwise the data or hole position is returned."""
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try:
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return os.lseek(file_obj.fileno(), offset, whence)
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except OSError as err:
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# The 'lseek' system call returns the ENXIO if there is no data or
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# hole starting from the specified offset.
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if err.errno == os.errno.ENXIO:
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return -1
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elif err.errno == os.errno.EINVAL:
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raise ErrorNotSupp("the kernel or file-system does not support "
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"\"SEEK_HOLE\" and \"SEEK_DATA\"")
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else:
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raise
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class FilemapSeek(_FilemapBase):
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"""
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This class uses the 'SEEK_HOLE' and 'SEEK_DATA' to find file block mapping.
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Unfortunately, the current implementation requires the caller to have write
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access to the image file.
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"""
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def __init__(self, image, log=None):
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"""Refer the '_FilemapBase' class for the documentation."""
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# Call the base class constructor first
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_FilemapBase.__init__(self, image, log)
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self._log.debug("FilemapSeek: initializing")
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self._probe_seek_hole()
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def _probe_seek_hole(self):
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"""
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Check whether the system implements 'SEEK_HOLE' and 'SEEK_DATA'.
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Unfortunately, there seems to be no clean way for detecting this,
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because often the system just fakes them by just assuming that all
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files are fully mapped, so 'SEEK_HOLE' always returns EOF and
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'SEEK_DATA' always returns the requested offset.
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I could not invent a better way of detecting the fake 'SEEK_HOLE'
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implementation than just to create a temporary file in the same
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directory where the image file resides. It would be nice to change this
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to something better.
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"""
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directory = os.path.dirname(self._image_path)
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try:
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tmp_obj = tempfile.TemporaryFile("w+", dir=directory)
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except IOError as err:
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raise ErrorNotSupp("cannot create a temporary in \"%s\": %s" \
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% (directory, err))
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try:
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os.ftruncate(tmp_obj.fileno(), self.block_size)
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except OSError as err:
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raise ErrorNotSupp("cannot truncate temporary file in \"%s\": %s"
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% (directory, err))
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offs = _lseek(tmp_obj, 0, _SEEK_HOLE)
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if offs != 0:
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# We are dealing with the stub 'SEEK_HOLE' implementation which
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# always returns EOF.
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self._log.debug("lseek(0, SEEK_HOLE) returned %d" % offs)
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raise ErrorNotSupp("the file-system does not support "
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"\"SEEK_HOLE\" and \"SEEK_DATA\" but only "
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"provides a stub implementation")
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tmp_obj.close()
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def block_is_mapped(self, block):
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"""Refer the '_FilemapBase' class for the documentation."""
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offs = _lseek(self._f_image, block * self.block_size, _SEEK_DATA)
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if offs == -1:
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result = False
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else:
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result = (offs // self.block_size == block)
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self._log.debug("FilemapSeek: block_is_mapped(%d) returns %s"
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% (block, result))
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return result
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def block_is_unmapped(self, block):
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"""Refer the '_FilemapBase' class for the documentation."""
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return not self.block_is_mapped(block)
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def _get_ranges(self, start, count, whence1, whence2):
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"""
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This function implements 'get_mapped_ranges()' and
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'get_unmapped_ranges()' depending on what is passed in the 'whence1'
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and 'whence2' arguments.
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"""
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assert whence1 != whence2
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end = start * self.block_size
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limit = end + count * self.block_size
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while True:
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start = _lseek(self._f_image, end, whence1)
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if start == -1 or start >= limit or start == self.image_size:
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break
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end = _lseek(self._f_image, start, whence2)
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if end == -1 or end == self.image_size:
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end = self.blocks_cnt * self.block_size
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if end > limit:
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end = limit
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start_blk = start // self.block_size
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end_blk = end // self.block_size - 1
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self._log.debug("FilemapSeek: yielding range (%d, %d)"
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% (start_blk, end_blk))
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yield (start_blk, end_blk)
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def get_mapped_ranges(self, start, count):
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"""Refer the '_FilemapBase' class for the documentation."""
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self._log.debug("FilemapSeek: get_mapped_ranges(%d, %d(%d))"
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% (start, count, start + count - 1))
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return self._get_ranges(start, count, _SEEK_DATA, _SEEK_HOLE)
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def get_unmapped_ranges(self, start, count):
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"""Refer the '_FilemapBase' class for the documentation."""
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self._log.debug("FilemapSeek: get_unmapped_ranges(%d, %d(%d))"
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% (start, count, start + count - 1))
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return self._get_ranges(start, count, _SEEK_HOLE, _SEEK_DATA)
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# Below goes the FIEMAP ioctl implementation, which is not very readable
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# because it deals with the rather complex FIEMAP ioctl. To understand the
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# code, you need to know the FIEMAP interface, which is documented in the
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# "Documentation/filesystems/fiemap.txt" file in the Linux kernel sources.
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# Format string for 'struct fiemap'
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_FIEMAP_FORMAT = "=QQLLLL"
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# sizeof(struct fiemap)
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_FIEMAP_SIZE = struct.calcsize(_FIEMAP_FORMAT)
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# Format string for 'struct fiemap_extent'
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_FIEMAP_EXTENT_FORMAT = "=QQQQQLLLL"
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# sizeof(struct fiemap_extent)
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_FIEMAP_EXTENT_SIZE = struct.calcsize(_FIEMAP_EXTENT_FORMAT)
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# The FIEMAP ioctl number
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_FIEMAP_IOCTL = 0xC020660B
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# This FIEMAP ioctl flag which instructs the kernel to sync the file before
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# reading the block map
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_FIEMAP_FLAG_SYNC = 0x00000001
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# Size of the buffer for 'struct fiemap_extent' elements which will be used
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# when invoking the FIEMAP ioctl. The larger is the buffer, the less times the
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# FIEMAP ioctl will be invoked.
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_FIEMAP_BUFFER_SIZE = 256 * 1024
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class FilemapFiemap(_FilemapBase):
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"""
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This class provides API to the FIEMAP ioctl. Namely, it allows to iterate
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over all mapped blocks and over all holes.
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This class synchronizes the image file every time it invokes the FIEMAP
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ioctl in order to work-around early FIEMAP implementation kernel bugs.
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"""
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def __init__(self, image, log=None):
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"""
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Initialize a class instance. The 'image' argument is full the file
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object to operate on.
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"""
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# Call the base class constructor first
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_FilemapBase.__init__(self, image, log)
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self._log.debug("FilemapFiemap: initializing")
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self._buf_size = _FIEMAP_BUFFER_SIZE
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# Calculate how many 'struct fiemap_extent' elements fit the buffer
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self._buf_size -= _FIEMAP_SIZE
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self._fiemap_extent_cnt = self._buf_size // _FIEMAP_EXTENT_SIZE
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assert self._fiemap_extent_cnt > 0
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self._buf_size = self._fiemap_extent_cnt * _FIEMAP_EXTENT_SIZE
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self._buf_size += _FIEMAP_SIZE
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# Allocate a mutable buffer for the FIEMAP ioctl
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self._buf = array.array('B', [0] * self._buf_size)
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# Check if the FIEMAP ioctl is supported
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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 == os.errno.EOPNOTSUPP:
|
||
|
|
errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
|
||
|
|
"by the file-system"
|
||
|
|
self._log.debug(errstr)
|
||
|
|
raise ErrorNotSupp(errstr)
|
||
|
|
if err.errno == os.errno.ENOTTY:
|
||
|
|
errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
|
||
|
|
"by the kernel"
|
||
|
|
self._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])
|
||
|
|
self._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."""
|
||
|
|
self._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:
|
||
|
|
self._log.debug("FilemapFiemap: yielding range (%d, %d)"
|
||
|
|
% (first_prev, last_prev))
|
||
|
|
yield (first_prev, last_prev)
|
||
|
|
first_prev, last_prev = first, last
|
||
|
|
|
||
|
|
self._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."""
|
||
|
|
self._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:
|
||
|
|
self._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:
|
||
|
|
self._log.debug("FilemapFiemap: yielding range (%d, %d)"
|
||
|
|
% (hole_first, start + count - 1))
|
||
|
|
yield (hole_first, start + count - 1)
|
||
|
|
|
||
|
|
def filemap(image, log=None):
|
||
|
|
"""
|
||
|
|
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, log)
|
||
|
|
except ErrorNotSupp:
|
||
|
|
return FilemapSeek(image, log)
|
||
|
|
|
||
|
|
def sparse_copy(src_fname, dst_fname, skip=0, seek=0,
|
||
|
|
length=0, api=None):
|
||
|
|
"""
|
||
|
|
Efficiently copy sparse file to or into another file.
|
||
|
|
|
||
|
|
src_fname: path to source file
|
||
|
|
dst_fname: path to destination file
|
||
|
|
skip: skip N bytes at thestart of src
|
||
|
|
seek: seek N bytes from the start of dst
|
||
|
|
length: read N bytes from src and write them to dst
|
||
|
|
api: FilemapFiemap or FilemapSeek object
|
||
|
|
"""
|
||
|
|
if not api:
|
||
|
|
api = filemap
|
||
|
|
fmap = api(src_fname)
|
||
|
|
try:
|
||
|
|
dst_file = open(dst_fname, 'r+b')
|
||
|
|
except IOError:
|
||
|
|
dst_file = open(dst_fname, 'wb')
|
||
|
|
if length:
|
||
|
|
dst_size = length + seek
|
||
|
|
else:
|
||
|
|
dst_size = os.path.getsize(src_fname) + seek - skip
|
||
|
|
dst_file.truncate(dst_size)
|
||
|
|
|
||
|
|
written = 0
|
||
|
|
for first, last in fmap.get_mapped_ranges(0, fmap.blocks_cnt):
|
||
|
|
start = first * fmap.block_size
|
||
|
|
end = (last + 1) * fmap.block_size
|
||
|
|
|
||
|
|
if skip >= end:
|
||
|
|
continue
|
||
|
|
|
||
|
|
if start < skip < end:
|
||
|
|
start = skip
|
||
|
|
|
||
|
|
fmap._f_image.seek(start, os.SEEK_SET)
|
||
|
|
|
||
|
|
written += start - skip - written
|
||
|
|
if length and written >= length:
|
||
|
|
dst_file.seek(seek + length, os.SEEK_SET)
|
||
|
|
dst_file.close()
|
||
|
|
return
|
||
|
|
|
||
|
|
dst_file.seek(seek + start - skip, os.SEEK_SET)
|
||
|
|
|
||
|
|
chunk_size = 1024 * 1024
|
||
|
|
to_read = end - start
|
||
|
|
read = 0
|
||
|
|
|
||
|
|
while read < to_read:
|
||
|
|
if read + chunk_size > to_read:
|
||
|
|
chunk_size = to_read - read
|
||
|
|
size = chunk_size
|
||
|
|
if length and written + size > length:
|
||
|
|
size = length - written
|
||
|
|
chunk = fmap._f_image.read(size)
|
||
|
|
dst_file.write(chunk)
|
||
|
|
read += size
|
||
|
|
written += size
|
||
|
|
if written == length:
|
||
|
|
dst_file.close()
|
||
|
|
return
|
||
|
|
dst_file.close()
|