Provided by: nbdkit_1.36.3-1ubuntu10_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).
AUTHORS
Richard W.M. Jones
COPYRIGHT
Copyright Red Hat
LICENSE
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