Provided by: nbdkit_1.42.2-1ubuntu1_amd64 
NAME
nbdkit-evil-filter - add random data corruption to reads
SYNOPSIS
nbdkit --filter=evil PLUGIN [PLUGIN-ARGS...]
evil=[cosmic-rays|stuck-bits|stuck-wires]
[evil-probability=PROB] [evil-stuck-probability=PROB]
[evil-seed=SEED]
DESCRIPTION
nbdkit-evil-filter is a Byzantine filter for nbdkit(1) that randomly corrupts data when reading from the
underlying plugin. This can be used for testing filesystem checksums. Note that it does not change
write operations, so the underlying plugin contains the correct data.
nbdkit-error-filter(1) is a related filter that injects hard errors into the NBD protocol.
This filter has several modes, controlled using the "evil=..." parameter. These are:
"evil=cosmic-rays"
Bits are flipped at random when reading data. The probability that a bit is flipped is controlled
using the "evil-probability" parameter, defaulting to 1e-8 (on average 1 in every 100 million bits
read is flipped).
"evil=stuck-bits"
This is the default mode.
Fixed bits in the backing file are stuck randomly high or low. The "evil-probability" parameter
controls the expected probability that a particular bit is stuck, defaulting in this mode to 1e-8 (1
in 100 million). "evil-stuck-probability" controls the probability that a stuck bit is read as its
stuck value or its correct value, defaulting to 100% (always read as a stuck bit).
"evil=stuck-wires"
This is similar to "stuck-bits" but instead of simulating bad backing data, it simulates stuck wires
along the data path (eg. in a register). The difference is that when reading, the stuck bit always
happens at the same position in the packet of data being read, regardless of where on the underlying
disk it is being read from. "evil-probability" controls the probability of a stuck wire, defaulting
in this mode to 1e-6 (1 in 1 million). "evil-stuck-probability" controls the probability that a
stuck bit is read as its stuck value or its correct value, defaulting to 100% (always read as a stuck
bit).
EXAMPLES
Add some stuck bits to the backing file at random:
nbdkit --filter=evil file disk.img
Cosmic rays will flip (on average) one in every 100 million bits copied from the backing file over NBD:
nbdkit --filter=evil file disk.img evil=cosmic-rays \
--run 'nbdcopy $uri output.img'
NOTES
Extents
Plugins can be sparse. This filter only corrupts bits in non-sparse parts of the backing disk and it
leaves sparse regions unchanged (which is realistic behaviour). If you wish to use this filter to
corrupt sparse regions, then combine this filter with nbdkit-noextents-filter(1). For example:
nbdkit --filter=evil --filter=noextents memory 1G
Probability limited to [ 1e-12 .. 1/8 ]
The current implementation limits probabilities to the range [ 1e-12 .. 1/8 ]. Values below this range
are treated the same as 0%. Values above this range are treated the same as 100%.
PARAMETERS
evil=cosmic-rays
evil=stuck-bits
evil=stuck-wires
Select the mode of evil. See the "DESCRIPTION" above. The default is "stuck-bits".
evil-probability=N
evil-probability=N:M
evil-probability=N%
Set the probability for the mode. You can either use a floating point number between 0 and 1, eg.
"evil-probability=0.001" or "evil-probability=1e-6". Or you can write it as N in M, eg.
"evil-probability=1:1000000" or "evil-probability=3.33:100000". Or you can write this as a
percentage, eg. "evil-probability=1%".
The default probability depends on the mode.
evil-seed=SEED
To make runs repeatable, use this to set a seed for the random number generator. Note that runs are
repeatable only if you use the same version of nbdkit, since in future we may change the algorithm.
The default is to choose a seed at random.
evil-stuck-probability=N
evil-stuck-probability=N:M
evil-stuck-probability=N%
For the "stuck-*" modes, the probability that when reading a stuck bit you will read the stuck bit or
the correct value. This defaults to 1 (ie. 100%) which means the bit is always stuck. Setting it to
0.5 for example will mean that half the time the bit appears stuck and half the time you see the
correct value.
FILES
$filterdir/nbdkit-evil-filter.so
The filter.
Use "nbdkit --dump-config" to find the location of $filterdir.
VERSION
"nbdkit-evil-filter" first appeared in nbdkit 1.36.
SEE ALSO
nbdkit(1), nbdkit-filter(3), nbdkit-delay-filter(1), nbdkit-noextents-filter(1), nbdkit-error-filter(1),
nbdkit_parse_probability(3).
AUTHORS
Richard W.M. Jones
COPYRIGHT
Copyright Red Hat
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,
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OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
DAMAGE.
nbdkit-1.42.2 2025-04-02 nbdkit-evil-filter(1)