Provided by: nbdkit_1.24.1-2ubuntu4_amd64 
NAME
nbdkit-data-plugin - nbdkit plugin for serving data from the command line
SYNOPSIS
nbdkit data [data=]'0 1 2 3 @0x1fe 0x55 0xaa'
[size=SIZE] [allocator=sparse|...]
nbdkit data base64='aGVsbG8gbmJka2l0IHVzZXI='
[size=SIZE] [allocator=sparse|...]
nbdkit data raw='binary_data'
[size=SIZE] [allocator=sparse|...]
DESCRIPTION
"nbdkit-data-plugin" is a plugin for nbdkit(1) which serves a small amount of data
specified directly on the command line. The plugin gets its name from the "data:" URI
scheme used by web browsers. This is mainly useful for testing NBD clients.
You can serve data read-only using the -r flag, or read-write. Any writes are thrown away
when nbdkit exits.
Most operating systems have command line size limits which are quite a lot smaller than
any desirable disk image, so specifying a large, fully populated disk image on the command
line would not be possible. However you can specify a small amount of data at the
beginning of the image, possibly followed by zeroes (using the "size" parameter to pad the
image to the full size), or use the "data" parameter creatively to make mostly sparse disk
images.
The "size" parameter can specify any virtual size up to the maximum supported by nbdkit
(2⁶³-1 bytes).
EXAMPLES
Create small disks filled with test patterns
nbdkit data ' ( 0x55 0xAA )*2048 '
nbdkit data ' ( "Hello" )*2000 ' size=8192
The first command creates a disk containing 4096 bytes filled with the repeating bytes
0x55 0xAA. The second command repeats "HelloHelloHello...", truncating the disk to
exactly 8192 bytes.
See also nbdkit-pattern-plugin(3).
Create a 1 MB disk with one empty MBR-formatted partition
nbdkit data '
@0x1b8 178 190 207 221 0 0 0 0 2 0 131 32 32 0 1 0 0 0 255 7
@0x1fe 85 170
' size=1M
This example was created by running:
$ rm -f disk
$ truncate -s 1M disk
$ echo start=1 | sfdisk disk
Device Boot Start End Sectors Size Id Type
disk1 1 2047 2047 1023.5K 83 Linux
$ ./disk2data.pl disk
The "disk2data.pl" script is provided in the nbdkit sources
(https://github.com/libguestfs/nbdkit/blob/master/plugins/data/disk2data.pl).
See also nbdkit-partitioning-plugin(1).
Create a disk image with sector-aligned data
nbdkit data ' <file1 @^512 <file2 @^512 <file3 @^512 '
Local binary files file1, file2 and file3 are copied into the disk image. Regardless of
the size of these files, they will all be aligned to 512-byte sector boundaries.
Furthermore because of the final alignment operation ("@^512") the total size of the disk
will also be rounded to a whole number of sectors.
Create a disk with the same random data in each sector
nbdkit data ' </dev/urandom[:512]*16 '
The expression "</dev/urandom[:512]" reads 512 bytes (one sector) of randomness from the
system. The same random data is repeated over 16 sectors.
Create a 1 MB disk with some nonsense data at the beginning
nbdkit data base64=MTIz size=1M
The above command serves the bytes "0x31 0x32 0x33" (which is the base64 decoding of
"MTIz"), followed by 1M - 3 bytes of zeroes.
"Hello, world" using this plugin
$ nbdkit data raw='Hello, world!' --run 'nbdcopy "$uri" - | cat'
Hello, world!
This works by creating a disk containing the string "Hello, world!". nbdcopy(1) connects
to the server using an NBD URI ("$uri") and copies the disk to stdout ("-"). The extra
cat(1) is needed because nbdcopy refuses to write raw disk data to a terminal.
PARAMETERS
Exactly one of the "data", "base64" or "raw" parameters must be supplied.
[data=]DATA
Specify the disk data using a simple compact format. See "DATA FORMAT" below.
"data=" is a magic config key and may be omitted in most cases. See "Magic
parameters" in nbdkit(1).
base64=BASE64
The "base64" parameter can be used to supply binary data encoded in base64 on the
command line.
This is only supported if nbdkit was compiled with GnuTLS ≥ 3.6.0. You can find out
by checking if:
$ nbdkit data --dump-plugin
contains:
data_base64=yes
raw=BINARY
The "raw" parameter can be used to supply raw binary data directly on the command
line.
It is usually quite difficult to do this unless you are running nbdkit from another
program (see nbdkit-captive(1)). One particular problem is that the data must not
contain zero bytes (ie. "\0") since those will be processed in C to mean the end of
the string. In almost all cases it is better to use base64 encoding or the custom
"data" format.
size=SIZE
The data is truncated or extended to the size specified.
This parameter is optional: If omitted the size is defined by the size of the "data",
"raw" or "base64" parameter.
allocator=sparse
allocator=malloc[,mlock=true]
allocator=zstd
(nbdkit ≥ 1.22)
Select the backend allocation strategy. See "ALLOCATORS" in nbdkit-memory-plugin(1).
The default is sparse.
DATA FORMAT
The "data" parameter lets you specify small disk images in a simple, compact format. It
is a string containing a list of bytes which are written into the disk image sequentially.
You can move the virtual offset where bytes are written using @offset.
For example:
nbdkit data '0 1 2 3 @0x1fe 0x55 0xaa'
creates a 0x200 = 512 byte (1 sector) image containing the four bytes "0 1 2 3" at the
start, and the two bytes "0x55 0xaa" at the end of the sector, with the remaining 506
bytes in the middle being all zeroes. In this example the size (512 bytes) is implied by
the data. But you could additionally use the "size" parameter to either truncate or
extend (with zeroes) the disk image.
Whitespace between fields in the string is ignored.
Fields in the string can be:
@OFFSET
Moves the current offset to "OFFSET". The offset may be specified as either decimal,
octal (prefixed by 0) or hexadecimal (prefixed by "0x"). Offset @0 is the first byte
of the disk.
@+N
@-N (nbdkit ≥ 1.22)
Add or subtract "N" from the current offset.
@^ALIGNMENT
(nbdkit ≥ 1.22)
If the current offset is not a multiple of "ALIGNMENT" then the offset is moved
forward to the next multiple. The next byte written will be aligned to "ALIGNMENT".
BYTE
Write "BYTE" at the current offset and advance the offset by 1 byte. The byte may be
specified as either decimal, octal (prefixed by 0) or hexadecimal (prefixed by "0x").
To add repeated bytes use "BYTE*N"
<FILE
(nbdkit ≥ 1.8)
Read the contents of binary FILE into the disk image at the current offset. The
offset is incremented by the size of the file. The filename can be a relative or
absolute path, but cannot contain whitespace in the name.
<(SCRIPT)
(nbdkit ≥ 1.24, not Windows)
Substitute the output of the shell script or external program as a binary blob and
advance the offset by the length in bytes of the output. You can use this to create
more complex test patterns. For example this produces a 32K disk image with an
incrementing test pattern in groups of 4 bytes:
nbdkit data ' <( i=0
while :; do
printf "%04d" $((i++))
done )[:32768] '
The script may contain "(" and ")" characters, but they must be in matching pairs. A
script can produce a finite amount of output; or (as in the example) an infinite
amount which must be truncated using the "[:len]" slice operator.
Scripts must be idempotent, producing the same output each time they are run. This is
because optimizations might change the order of evaluation or number of times the
script is called and you could get different output in a future version of nbdkit.
"STRING"
(nbdkit ≥ 1.22)
Write a string into the image at the current offset and advance the offset by the
length of the string. To include special characters in the string you can escape them
in the same way as C strings (eg. a double quote character within the string should be
written "\""). Be careful with shell quoting around the whole data parameter.
( ... )
(nbdkit ≥ 1.24)
Group a set of expressions into a single expression.
"( ... )" recursively creates a new data parser so any of the above operators can
appear inside, including nested "( ... )". Note that offsets and alignments within
the subpattern are relative to the start of the subpattern, not relative to the final
disk image.
expression * N
(nbdkit ≥ 1.24)
Repeat the expression "N" times. The offset is incremented by the length of the
expression × N. For example to create a repeating pattern of 0x55, 0xAA for 512
(2×256) bytes do:
nbdkit data '( 0x55 0xAA ) * 256'
expression [N:M]
(nbdkit ≥ 1.24)
Take a slice of the expression. Slices are [start:end+1] where start and end are the
first and last byte offsets of the expression desired. Either or both may be omitted.
[:len] means to take the first len bytes. [start:] means to take bytes from offset
start to the end of the expression.
expression -> \NAME
\NAME
(nbdkit ≥ 1.24)
Assign an expression to a name which can be used later. Names can be used in the
current scope (or any scopes nested within the current scope), but disappear at the
end of the current scope. Names start with a backslash character followed by one or
more alphanumeric, dash and underscore. For example this makes two identical sectors
both containing a boot signature at the end:
nbdkit data ' ( 0x55 0xAA ) -> \boot-signature
( @0x1fe \boot-signature ) -> \sector
\sector \sector '
$VAR
(nbdkit ≥ 1.24)
Substitute command line parameters or environment variables. The variable is written
in the same language as the "data" parameter, and when substituted it creates a nested
scope like "( ... )" expressions. These are all equivalent:
nbdkit data '$pattern*16' pattern='0x55 0xAA'
export pattern='0x55 0xAA'
nbdkit data '$pattern*16'
nbdkit data '( 0x55 0xAA )*16'
# COMMENT
(nbdkit ≥ 1.24)
"#" begins a comment stretching to the end of the current line.
disk2data.pl script
This script can convert from small disk images into the data format described above.
It is provided in the nbdkit sources. See
https://github.com/libguestfs/nbdkit/blob/master/plugins/data/disk2data.pl
FILES
$plugindir/nbdkit-data-plugin.so
The plugin.
Use "nbdkit --dump-config" to find the location of $plugindir.
VERSION
"nbdkit-data-plugin" first appeared in nbdkit 1.6.
SEE ALSO
nbdkit(1), nbdkit-captive(1), nbdkit-plugin(3), nbdkit-info-plugin(1),
nbdkit-memory-plugin(1), nbdkit-null-plugin(1), nbdkit-partitioning-plugin(1),
nbdkit-pattern-plugin(1), nbdkit-random-plugin(1), nbdkit-sparse-random-plugin(1),
nbdkit-tmpdisk-plugin(1), nbdkit-zero-plugin(1),
https://github.com/libguestfs/nbdkit/blob/master/plugins/data/disk2data.pl,
https://en.wikipedia.org/wiki/Base64.
AUTHORS
Richard W.M. Jones
COPYRIGHT
Copyright (C) 2018-2020 Red Hat Inc.
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.