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This module implements the block map (bmap) creation functionality and provides
the corresponding API in form of the 'BmapCreate' class.
The idea is that while images files may generally be very large (e.g., 4GiB),
they may nevertheless contain only little real data, e.g., 512MiB. This data
are files, directories, file-system meta-data, partition table, etc. When
copying the image to the target device, you do not have to copy all the 4GiB of
data, you can copy only 512MiB of it, which is 4 times less, so copying should
presumably be 4 times faster.
The block map file is an XML file which contains a list of blocks which have to
be copied to the target device. The other blocks are not used and there is no
need to copy them. The XML file also contains some additional information like
block size, image size, count of mapped blocks, etc. There are also many
commentaries, so it is human-readable.
The image has to be a sparse file. Generally, this means that when you generate
this image file, you should start with a huge sparse file which contains a
single hole spanning the entire file. Then you should partition it, write all
the data (probably by means of loop-back mounting the image or parts of it),
etc. The end result should be a sparse file where mapped areas represent useful
parts of the image and holes represent useless parts of the image, which do not
have to be copied when copying the image to the target device.
This module uses the FIEMAP ioctl to detect holes.
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A class for exceptions generated by this module. We currently support only
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description in case of errors.
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This class implements the bmap creation functionality. To generate a bmap
for an image (which is supposedly a sparse file), you should first create
an instance of 'BmapCreate' and provide:
* full path or a file-like object of the image to create bmap for
* full path or a file object to use for writing the results to
Then you should invoke the 'generate()' method of this class. It will use
the FIEMAP ioctl to generate the bmap.
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Initialize a class instance:
* image - full path or a file-like object of the image to create bmap
for
* bmap - full path or a file object to use for writing the resulting
bmap to
* chksum - type of the check sum to use in the bmap file (all checksum
types which python's "hashlib" module supports are allowed).
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A helper function which generates the starting contents of the block
map file: the header comment, image size, block size, etc.
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A helper function which generates the final parts of the block map
file: the ending tags and the information about the amount of mapped
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A helper function which calculates checksum for the range of blocks of
the image file: from block 'first' to block 'last'.
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Generate bmap for the image file. If 'include_checksums' is 'True',
also generate checksums for block ranges.
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