• NAME
• SYNOPSIS
• DESCRIPTION
• EXAMPLE
  • Swap bytes from a disk image
• PARAMETERS
• FILES
• VERSION
• SEE ALSO
• AUTHORS
• COPYRIGHT
• LICENSE

NAME

nbdkit-swab-filter - nbdkit filter for swapping byte order

SYNOPSIS

 nbdkit --filter=swab PLUGIN [PLUGIN-ARGS...] [swab-bits=8|16|32|64]

DESCRIPTION

nbdkit-swab-filter is a filter for nbdkit(1) which swaps bytes in the underlying plugin.

One use for this is to read disk images which were formatted on the Atari Falcon, where the IDE controller is wired in reverse order.

EXAMPLE

Swap bytes from a disk image

 nbdkit --filter=swab file file=disk.img

The above command serves the disk image disk.img, swapping even and odd bytes:

 disk.img   0   1   2   3   4   5 ...
              ╳       ╳       ╳
   output   1   0   3   2   5   4 ...

This filter truncates the size of the plugin down to the alignment determined by swab-bits (since operating on an unaligned tail would be awkward). If you need to round the image size up instead to access the last few bytes, combine this filter with nbdkit-truncate-filter(1); fortunately, sector-based disk images are already suitably sized.

Note that this filter fails operations where the offset or count are not aligned to the swab-bits boundaries; if you need byte-level access, apply the nbdkit-blocksize-filter(1) before this one, to get read-modify-write access to individual bytes.

PARAMETERS

swab-bits=8

This turns off the filter.

swab-bits=16

This is the default setting which swaps pairs of bytes. This is suitable when reading and writing to Atari Falcon drives.

swab-bits=32

This swaps the endianness of each 4 byte word in the disk, ie:

  input    0   1   2   3   4   5   6   7

 output    3   2   1   0   7   6   5   4

swab-bits=64

This swaps the endianness of each 8 byte word in the disk, ie:

  input    0   1   2   3   4   5   6   7

 output    7   6   5   4   3   2   1   0

This can be used to make nbdkit-pattern-plugin(1) little endian instead of big endian.

FILES

$filterdir/nbdkit-swab-filter.so

The filter.

Use nbdkit --dump-config to find the location of $filterdir.

VERSION

nbdkit-swab-filter first appeared in nbdkit 1.22.

SEE ALSO

nbdkit(1), nbdkit-file-plugin(1), nbdkit-pattern-plugin(1), nbdkit-filter(3), nbdkit-blocksize-filter(1). nbdkit-truncate-filter(1).

AUTHORS

François Revol

COPYRIGHT

Copyright (C) 2020 François Revol

LICENSE

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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