• NAME
• SYNOPSIS
• DESCRIPTION
  • Strides
  • Writes and testing copying
  • Largest possible size
  • Little endian pattern
• PARAMETERS
• FILES
• VERSION
• SEE ALSO
• AUTHORS
• COPYRIGHT
• LICENSE

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.

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.

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-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.