299 lines
11 KiB
Python
299 lines
11 KiB
Python
""" This module implements the block map (bmap) creation functionality and
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provides the corresponding API in form of the 'BmapCreate' class.
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The idea is that while images files may generally be very large (e.g., 4GiB),
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they may nevertheless contain only little real data, e.g., 512MiB. This data
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are files, directories, file-system meta-data, partition table, etc. When
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copying the image to the target device, you do not have to copy all the 4GiB of
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data, you can copy only 512MiB of it, which is 4 times less, so copying should
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presumably be 4 times faster.
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The block map file is an XML file which contains a list of blocks which have to
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be copied to the target device. The other blocks are not used and there is no
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need to copy them. The XML file also contains some additional information like
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block size, image size, count of mapped blocks, etc. There are also many
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commentaries, so it is human-readable.
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The image has to be a sparse file. Generally, this means that when you generate
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this image file, you should start with a huge sparse file which contains a
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single hole spanning the entire file. Then you should partition it, write all
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the data (probably by means of loop-back mounting the image or parts of it),
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etc. The end result should be a sparse file where mapped areas represent useful
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parts of the image and holes represent useless parts of the image, which do not
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have to be copied when copying the image to the target device.
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This module uses the FIBMAP ioctl to detect holes. """
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# Disable the following pylint recommendations:
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# * Too many instance attributes - R0902
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# * Too few public methods - R0903
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# pylint: disable=R0902,R0903
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import hashlib
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from mic.utils.misc import human_size
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from mic.utils import Fiemap
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# The bmap format version we generate
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SUPPORTED_BMAP_VERSION = "1.3"
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_BMAP_START_TEMPLATE = \
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"""<?xml version="1.0" ?>
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<!-- This file contains the block map for an image file, which is basically
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a list of useful (mapped) block numbers in the image file. In other words,
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it lists only those blocks which contain data (boot sector, partition
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table, file-system metadata, files, directories, extents, etc). These
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blocks have to be copied to the target device. The other blocks do not
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contain any useful data and do not have to be copied to the target
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device.
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The block map an optimization which allows to copy or flash the image to
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the image quicker than copying of flashing the entire image. This is
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because with bmap less data is copied: <MappedBlocksCount> blocks instead
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of <BlocksCount> blocks.
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Besides the machine-readable data, this file contains useful commentaries
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which contain human-readable information like image size, percentage of
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mapped data, etc.
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The 'version' attribute is the block map file format version in the
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'major.minor' format. The version major number is increased whenever an
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incompatible block map format change is made. The minor number changes
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in case of minor backward-compatible changes. -->
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<bmap version="%s">
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<!-- Image size in bytes: %s -->
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<ImageSize> %u </ImageSize>
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<!-- Size of a block in bytes -->
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<BlockSize> %u </BlockSize>
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<!-- Count of blocks in the image file -->
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<BlocksCount> %u </BlocksCount>
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"""
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class Error(Exception):
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""" A class for exceptions generated by this module. We currently support
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only one type of exceptions, and we basically throw human-readable problem
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description in case of errors. """
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pass
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class BmapCreate:
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""" This class implements the bmap creation functionality. To generate a
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bmap for an image (which is supposedly a sparse file), you should first
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create an instance of 'BmapCreate' and provide:
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* full path or a file-like object of the image to create bmap for
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* full path or a file object to use for writing the results to
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Then you should invoke the 'generate()' method of this class. It will use
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the FIEMAP ioctl to generate the bmap. """
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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 _open_bmap_file(self):
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""" Open the bmap file. """
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try:
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self._f_bmap = open(self._bmap_path, 'w+')
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except IOError as err:
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raise Error("cannot open bmap file '%s': %s" \
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% (self._bmap_path, err))
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self._f_bmap_needs_close = True
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def __init__(self, image, bmap):
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""" Initialize a class instance:
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* image - full path or a file-like object of the image to create bmap
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for
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* bmap - full path or a file object to use for writing the resulting
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bmap to """
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self.image_size = None
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self.image_size_human = None
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self.block_size = None
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self.blocks_cnt = None
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self.mapped_cnt = None
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self.mapped_size = None
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self.mapped_size_human = None
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self.mapped_percent = None
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self._mapped_count_pos1 = None
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self._mapped_count_pos2 = None
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self._sha1_pos = None
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self._f_image_needs_close = False
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self._f_bmap_needs_close = False
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if hasattr(image, "read"):
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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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if hasattr(bmap, "read"):
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self._f_bmap = bmap
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self._bmap_path = bmap.name
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else:
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self._bmap_path = bmap
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self._open_bmap_file()
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self.fiemap = Fiemap.Fiemap(self._f_image)
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self.image_size = self.fiemap.image_size
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self.image_size_human = human_size(self.image_size)
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if self.image_size == 0:
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raise Error("cannot generate bmap for zero-sized image file '%s'" \
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% self._image_path)
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self.block_size = self.fiemap.block_size
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self.blocks_cnt = self.fiemap.blocks_cnt
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def _bmap_file_start(self):
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""" A helper function which generates the starting contents of the
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block map file: the header comment, image size, block size, etc. """
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# We do not know the amount of mapped blocks at the moment, so just put
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# whitespaces instead of real numbers. Assume the longest possible
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# numbers.
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mapped_count = ' ' * len(str(self.image_size))
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mapped_size_human = ' ' * len(self.image_size_human)
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xml = _BMAP_START_TEMPLATE \
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% (SUPPORTED_BMAP_VERSION, self.image_size_human,
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self.image_size, self.block_size, self.blocks_cnt)
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xml += " <!-- Count of mapped blocks: "
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self._f_bmap.write(xml)
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self._mapped_count_pos1 = self._f_bmap.tell()
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# Just put white-spaces instead of real information about mapped blocks
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xml = "%s or %.1f -->\n" % (mapped_size_human, 100.0)
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xml += " <MappedBlocksCount> "
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self._f_bmap.write(xml)
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self._mapped_count_pos2 = self._f_bmap.tell()
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xml = "%s </MappedBlocksCount>\n\n" % mapped_count
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# pylint: disable=C0301
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xml += " <!-- The checksum of this bmap file. When it is calculated, the value of\n"
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xml += " the SHA1 checksum has be zeoro (40 ASCII \"0\" symbols). -->\n"
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xml += " <BmapFileSHA1> "
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self._f_bmap.write(xml)
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self._sha1_pos = self._f_bmap.tell()
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xml = "0" * 40 + " </BmapFileSHA1>\n\n"
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xml += " <!-- The block map which consists of elements which may either be a\n"
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xml += " range of blocks or a single block. The 'sha1' attribute (if present)\n"
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xml += " is the SHA1 checksum of this blocks range. -->\n"
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xml += " <BlockMap>\n"
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# pylint: enable=C0301
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self._f_bmap.write(xml)
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def _bmap_file_end(self):
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""" A helper function which generates the final parts of the block map
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file: the ending tags and the information about the amount of mapped
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blocks. """
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xml = " </BlockMap>\n"
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xml += "</bmap>\n"
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self._f_bmap.write(xml)
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self._f_bmap.seek(self._mapped_count_pos1)
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self._f_bmap.write("%s or %.1f%%" % \
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(self.mapped_size_human, self.mapped_percent))
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self._f_bmap.seek(self._mapped_count_pos2)
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self._f_bmap.write("%u" % self.mapped_cnt)
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self._f_bmap.seek(0)
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sha1 = hashlib.sha1(self._f_bmap.read()).hexdigest()
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self._f_bmap.seek(self._sha1_pos)
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self._f_bmap.write("%s" % sha1)
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def _calculate_sha1(self, first, last):
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""" A helper function which calculates SHA1 checksum for the range of
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blocks of the image file: from block 'first' to block 'last'. """
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start = first * self.block_size
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end = (last + 1) * self.block_size
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self._f_image.seek(start)
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hash_obj = hashlib.new("sha1")
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chunk_size = 1024*1024
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to_read = end - start
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read = 0
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while read < to_read:
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if read + chunk_size > to_read:
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chunk_size = to_read - read
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chunk = self._f_image.read(chunk_size)
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hash_obj.update(chunk)
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read += chunk_size
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return hash_obj.hexdigest()
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def generate(self, include_checksums = True):
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""" Generate bmap for the image file. If 'include_checksums' is 'True',
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also generate SHA1 checksums for block ranges. """
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# Save image file position in order to restore it at the end
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image_pos = self._f_image.tell()
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self._bmap_file_start()
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# Generate the block map and write it to the XML block map
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# file as we go.
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self.mapped_cnt = 0
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for first, last in self.fiemap.get_mapped_ranges(0, self.blocks_cnt):
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self.mapped_cnt += last - first + 1
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if include_checksums:
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sha1 = self._calculate_sha1(first, last)
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sha1 = " sha1=\"%s\"" % sha1
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else:
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sha1 = ""
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if first != last:
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self._f_bmap.write(" <Range%s> %s-%s </Range>\n" \
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% (sha1, first, last))
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else:
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self._f_bmap.write(" <Range%s> %s </Range>\n" \
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% (sha1, first))
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self.mapped_size = self.mapped_cnt * self.block_size
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self.mapped_size_human = human_size(self.mapped_size)
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self.mapped_percent = (self.mapped_cnt * 100.0) / self.blocks_cnt
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self._bmap_file_end()
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try:
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self._f_bmap.flush()
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except IOError as err:
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raise Error("cannot flush the bmap file '%s': %s" \
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% (self._bmap_path, err))
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self._f_image.seek(image_pos)
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def __del__(self):
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""" The class destructor which closes the opened files. """
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if self._f_image_needs_close:
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self._f_image.close()
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if self._f_bmap_needs_close:
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self._f_bmap.close()
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