nbdkit-pattern-plugin(1)

NAME
nbdkit-pattern-plugin - plugin to serve a fixed pattern of data for testing

SYNOPSIS
 nbdkit pattern [size=]SIZE [stride=BLOCK_SIZE]

DESCRIPTION
"nbdkit-pattern-plugin" is a plugin for nbdkit(1) which serves a fixed pattern of data, read only. This is used for testing nbdkit filters and NBD clients.

To create test disks filled with other repeated patterns use nbdkit-data-plugin(1) or nbdkit-ones-plugin(1) instead. To create disks filled with random data, use nbdkit-random-plugin(1) or nbdkit-sparse-random-plugin(1).

The fixed pattern is the offset, as a 64 bit big endian integer, every 8 bytes. In hexadecimal this looks like:

 offset                         data
  0000:   00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 08
  0010:   00 00 00 00 00 00 00 10   00 00 00 00 00 00 00 18
  0020:   00 00 00 00 00 00 00 20   00 00 00 00 00 00 00 28
                                  ↗ └──────────┬──────────┘
              byte at offset 0x28              │
                                               │
                                     64 bit big endian int
                                     encoding offset 0x28

The size of the virtual disk must be specified using the "size" parameter. If the size is not a multiple of 8 then the last 8 byte offset in the pattern is truncated.

  Upper bits
The "upper" parameter can be used to set the top 16 bits of each word in the pattern. This can be used to distinguish between different instances of nbdkit-pattern-plugin, or when testing copies to ensure that different data is copied each time. For example setting "upper=0x1234" changes the pattern to:

 offset                         data
  0000:   12 34 00 00 00 00 00 00   12 34 00 00 00 00 00 08
  0010:   12 34 00 00 00 00 00 10   12 34 00 00 00 00 00 18
  0020:   12 34 00 00 00 00 00 20   12 34 00 00 00 00 00 28

The upper value is XOR-ed into the top 16 bits, the default is 0.

  Strides
Using the "stride" parameter you can create a pattern where each block of data has a unique number. This is useful for tracking down disk corruption where blocks of data may be transposed. For example, with 4096 byte block-based storage, using "stride=4k" will produce a pattern like this:

 offset                         data
  0000:   00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 00
  0010:   00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 00
  ...
  ...                          block at offset 0x1000 (4k)
  ...                        ↙
  1000:   00 00 00 00 00 00 10 00   00 00 00 00 00 00 00 00
  1010:   00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 00
  ...
  ...                          block at offset 0x2000 (8k)
  ...                        ↙
  2000:   00 00 00 00 00 00 20 00   00 00 00 00 00 00 00 00
  2010:   00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 00

  Writes and testing copying
Writing to the disk is possible. If you do this the plugin will check that what you are writing exactly matches what would be read at the same offset (if not, it returns EIO error). You can use this to test copying programs by making the source and destination NBD URIs be the same:

 nbdkit pattern size=100M --run 'nbdcopy "$uri" "$uri"'

"qemu-img convert" could be used in place of nbdcopy. See also nbdkit-checkwrite-filter(1).

  Largest possible size
nbdkit itself limits plugins to 2⁶³-1 bytes (decimal: 9223372036854775807, hexadecimal: 0x7fff_ffff_ffff_ffff).

To test if NBD clients are free of bugs (not to mention nbdkit itself) you can use:

 nbdkit pattern 9223372036854775807

Note this is too large for qemu to open.

  Little endian pattern
To get a little endian pattern instead of big endian apply nbdkit-swab-filter(1) on top of this plugin:

 nbdkit pattern 1G --filter=swab swab-bits=64

PARAMETERS

[size=]SIZE
    Specify the virtual size of the disk image.

    This parameter is required.

    "size=" prefix may be omitted in most cases. See "Magic parameters" in nbdkit(1).

stride=BLOCK_SIZE
    Instead of writing the 64 bit integers sequentially, place them at the beginning of each "BLOCK_SIZE" block. See "Strides" above.

    The minimum, and default, stride is 8 which places the integers sequentially with no gaps. The stride must be a power of two.

upper=N
    XOR "N" (N=0..65535) with the top 16 bits of the pattern word. You can prefix the value with "0x" for hexadecimal. The default is 0.

upper=random
    On each run of nbdkit, a random number in the range 1..65535 (not 0) is chosen for the upper 16 bits of each word.

FILES

$plugindir/nbdkit-pattern-plugin.so
    The plugin.

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

VERSION
"nbdkit-pattern-plugin" first appeared in nbdkit 1.6.

SEE ALSO
nbdkit(1), nbdkit-plugin(3), nbdkit-checkwrite-filter(1), nbdkit-data-plugin(1), nbdkit-full-plugin(1), nbdkit-null-plugin(1), nbdkit-ones-plugin(1), nbdkit-offset-filter(1), nbdkit-random-plugin(1), nbdkit-sparse-random-plugin(1), nbdkit-swab-filter(1), nbdkit-xor-filter(1), nbdkit-zero-plugin(1).

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, 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.