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nbdkit-evil-filter - Man Page

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

License

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

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.

Referenced By

nbdkit(1), nbdkit-error-filter(1), nbdkit-filter(3), nbdkit_parse_probability(3), nbdkit-release-notes-1.36(1).

2024-05-17 nbdkit-1.39.6