nbdkit-swab-filter(1)

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.

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.