1nbdkit-data-plugin(1)               NBDKIT               nbdkit-data-plugin(1)
2
3
4

NAME

6       nbdkit-data-plugin - nbdkit plugin for serving data from the command
7       line
8

SYNOPSIS

10        nbdkit data [data=]'0 1 2 3 @0x1fe 0x55 0xaa'
11                    [size=SIZE] [allocator=sparse|malloc|zstd]
12
13        nbdkit data base64='aGVsbG8gbmJka2l0IHVzZXI='
14                    [size=SIZE] [allocator=sparse|malloc|zstd]
15
16        nbdkit data raw='binary_data'
17                    [size=SIZE] [allocator=sparse|malloc|zstd]
18

DESCRIPTION

20       "nbdkit-data-plugin" is a plugin for nbdkit(1) which serves a small
21       amount of data specified directly on the command line.  The plugin gets
22       its name from the "data:" URI scheme used by web browsers.  This is
23       mainly useful for testing NBD clients.
24
25       You can serve data read-only using the -r flag, or read-write.  Any
26       writes are thrown away when nbdkit exits.
27
28       Most operating systems have command line size limits which are quite a
29       lot smaller than any desirable disk image, so specifying a large, fully
30       populated disk image on the command line would not be possible.
31       However you can specify a small amount of data at the beginning of the
32       image, possibly followed by zeroes (using the "size" parameter to pad
33       the image to the full size), or use the "data" parameter creatively to
34       make mostly sparse disk images.
35
36       The "size" parameter can specify any virtual size up to the maximum
37       supported by nbdkit (2⁶³-1 bytes).
38

EXAMPLES

40   Create small disks filled with test patterns
41        nbdkit data ' ( 0x55 0xAA )*2048 '
42        nbdkit data ' ( "Hello" )*2000 ' size=8192
43
44       The first command creates a disk containing 4096 bytes filled with the
45       repeating bytes 0x55 0xAA.  The second command repeats
46       "HelloHelloHello...", truncating the disk to exactly 8192 bytes.
47
48       See also nbdkit-pattern-plugin(3).
49
50   Create a 1 MB disk with MBR-format partition table
51        nbdkit data '
52          @0x1be    # MBR first partition entry
53            0           # Partition status
54            0 2 0       # CHS start
55            0x83        # Partition type (Linux)
56            0x20 0x20 0 # CHS last sector
57            le32:1      # LBA first sector
58            le32:0x7ff  # LBA number of sectors
59          @0x1fe    # Boot signature
60            0x55 0xaa
61          ' size=1M
62
63       A more flexible way to create partitions is to use
64       nbdkit-partitioning-plugin(1).  To create a data string from an
65       existing disk use the "disk2data.pl" script provided in the nbdkit
66       sources
67       (https://gitlab.com/nbdkit/nbdkit/blob/master/plugins/data/disk2data.pl).
68
69   Create a disk image with sector-aligned data
70        nbdkit data ' <file1 @^512 <file2 @^512 <file3 @^512 '
71
72       Local binary files file1, file2 and file3 are copied into the disk
73       image.  Regardless of the size of these files, they will all be aligned
74       to 512-byte sector boundaries.  Furthermore because of the final
75       alignment operation ("@^512") the total size of the disk will also be
76       rounded to a whole number of sectors.
77
78   Create a disk with the same random data in each sector
79        nbdkit data ' </dev/urandom[:512]*16 '
80
81       The expression "</dev/urandom[:512]" reads 512 bytes (one sector) of
82       randomness from the system.  The same random data is repeated over 16
83       sectors.
84
85   Create a 1 MB disk with some nonsense data at the beginning
86        nbdkit data base64=MTIz size=1M
87
88       The above command serves the bytes "0x31 0x32 0x33" (which is the
89       base64 decoding of "MTIz"), followed by 1M - 3 bytes of zeroes.
90
91   "Hello, world" using this plugin
92        $ nbdkit data raw='Hello, world!' --run 'nbdcopy "$uri" - | cat'
93        Hello, world!
94
95       This works by creating a disk containing the string "Hello, world!".
96       nbdcopy(1) connects to the server using an NBD URI ("$uri") and copies
97       the disk to stdout ("-").  The extra cat(1) is needed because nbdcopy
98       refuses to write raw disk data to a terminal.
99

PARAMETERS

101       Exactly one of the "data", "base64" or "raw" parameters must be
102       supplied.
103
104       [data=]DATA
105           Specify the disk data using a simple compact format.  See "DATA
106           FORMAT" below.
107
108           "data=" is a magic config key and may be omitted in most cases.
109           See "Magic parameters" in nbdkit(1).
110
111       base64=BASE64
112           The "base64" parameter can be used to supply binary data encoded in
113           base64 on the command line.
114
115           This is only supported if nbdkit was compiled with GnuTLS ≥ 3.6.0.
116           You can find out by checking if:
117
118            $ nbdkit data --dump-plugin
119
120           contains:
121
122            data_base64=yes
123
124       raw=BINARY
125           The "raw" parameter can be used to supply raw binary data directly
126           on the command line.
127
128           It is usually quite difficult to do this unless you are running
129           nbdkit from another program (see nbdkit-captive(1)).  One
130           particular problem is that the data must not contain zero bytes
131           (ie. "\0") since those will be processed in C to mean the end of
132           the string.  In almost all cases it is better to use base64
133           encoding or the custom "data" format.
134
135       size=SIZE
136           The data is truncated or extended to the size specified.
137
138           This parameter is optional: If omitted the size is defined by the
139           size of the "data", "raw" or "base64" parameter.
140
141       allocator=sparse
142       allocator=malloc[,mlock=true]
143       allocator=zstd
144           (nbdkit ≥ 1.22)
145
146           Select the backend allocation strategy.  See "ALLOCATORS" in
147           nbdkit-memory-plugin(1).  The default is sparse.
148

DATA FORMAT

150       The "data" parameter lets you specify small disk images in a simple,
151       compact format.  It is a string containing a list of bytes which are
152       written into the disk image sequentially.  You can move the virtual
153       offset where bytes are written using @offset.
154
155        nbdkit data '0 1 2 3 @0x1fe 0x55 0xaa'
156
157       creates:
158
159                    total size 0x200 = 512 bytes (1 sector)
160       ┌──────┬──────┬──────┬──────┬───────── ── ── ───┬──────┬──────┐
161       │   0  │   1  │   2  │   3  │  0     0  ...  0  │ 0x55 │ 0xaa │
162       └──────┴──────┴──────┴──────┴───────── ── ── ───┴──────┴──────┘
163
164                                                   offset 0x1fe
165
166       In this example the size is implied by the data.  But you could also
167       use the "size" parameter to either truncate or extend (with zeroes) the
168       disk image.  Another way to write the same disk would be this, where we
169       align the offset to the end of the sector and move back 2 bytes to
170       write the signature:
171
172        nbdkit data '0 1 2 3 @^0x200 @-2 le16:0xaa55'
173
174       Fields in the string can be:
175
176       BYTE
177           Write a byte at the current offset and advance the offset by 1.
178           The byte may be specified as either decimal, octal (prefixed by 0)
179           or hexadecimal (prefixed by "0x").  To add repeated bytes use the
180           "*" operator (eg. "0xFF*16").
181
182       le16:WORD
183       be16:WORD
184       le32:WORD
185       be32:WORD
186       le64:WORD
187       be64:WORD
188           (nbdkit ≥ 1.28)
189
190           Write a word expressed in little endian (le) or big endian (be) of
191           length 16/32/64 bits and advance the offset by 2/4/8.  The word may
192           be specified in decimal, octal or hexadecimal.  For example:
193
194            nbdkit data ' be32:0x1 '
195
196           generates the 4 byte sequence "0 0 0 1".
197
198       @OFFSET
199           Moves the current offset to "OFFSET".  The offset may be specified
200           as either decimal, octal (prefixed by 0) or hexadecimal (prefixed
201           by "0x").  Offset @0 is the first byte of the disk.
202
203       @+N
204       @-N (nbdkit ≥ 1.22)
205
206           Add or subtract "N" from the current offset.
207
208       @^ALIGNMENT
209           (nbdkit ≥ 1.22)
210
211           If the current offset is not a multiple of "ALIGNMENT" then the
212           offset is moved forward to the next multiple.  The next byte
213           written will be aligned to "ALIGNMENT".
214
215       <FILE
216           (nbdkit ≥ 1.8)
217
218           Read the contents of binary FILE into the disk image at the current
219           offset.  The offset is incremented by the size of the file.  The
220           filename can be a relative or absolute path, but cannot contain
221           whitespace in the name.
222
223       <(SCRIPT)
224           (nbdkit ≥ 1.24, not Windows)
225
226           Substitute the output of the shell script or external program as a
227           binary blob and advance the offset by the length in bytes of the
228           output.  You can use this to create more complex test patterns.
229           For example this produces a 32K disk image with an incrementing
230           test pattern in groups of 4 bytes:
231
232            nbdkit data ' <( i=0
233                             while :; do
234                                 printf "%04d" $((i++))
235                             done )[:32768] '
236
237           The script may contain "(" and ")" characters, but they must be in
238           matching pairs.  A script can produce a finite amount of output; or
239           (as in the example) an infinite amount which must be truncated
240           using the "[:len]" slice operator.
241
242           Scripts must be idempotent, producing the same output each time
243           they are run.  This is because optimizations might change the order
244           of evaluation or number of times the script is called and you could
245           get different output in a future version of nbdkit.
246
247       "STRING"
248           (nbdkit ≥ 1.22)
249
250           Write a string into the image at the current offset and advance the
251           offset by the length of the string.  To include special characters
252           in the string you can escape them in the same way as C strings (eg.
253           a double quote character within the string should be written "\"").
254           Be careful with shell quoting around the whole data parameter.
255
256       ( ... )
257           (nbdkit ≥ 1.24)
258
259           Group a set of expressions into a single expression.
260
261           "( ... )" recursively creates a new data parser so any of the above
262           operators can appear inside, including nested "( ... )".  Note that
263           offsets and alignments within the subpattern are relative to the
264           start of the subpattern, not relative to the final disk image.
265
266       expression * N
267           (nbdkit ≥ 1.24)
268
269           Repeat the expression "N" times.  The offset is incremented by the
270           length of the expression × N.  For example to create a repeating
271           pattern of 0x55, 0xAA for 512 (2×256) bytes do:
272
273            nbdkit data '( 0x55 0xAA ) * 256'
274
275       expression [N:M]
276           (nbdkit ≥ 1.24)
277
278           Take a slice of the expression.  Slices are [start:end+1] where
279           start and end are the first and last byte offsets of the expression
280           desired.  Either or both may be omitted.  [:len] means to take the
281           first len bytes.  [start:] means to take bytes from offset start to
282           the end of the expression.
283
284       expression -> \NAME
285       \NAME
286           (nbdkit ≥ 1.24)
287
288           Assign an expression to a name which can be used later.  Names can
289           be used in the current scope (or any scopes nested within the
290           current scope), but disappear at the end of the current scope.
291           Names start with a backslash character followed by one or more
292           alphanumeric, dash and underscore.  For example this makes two
293           identical sectors both containing a boot signature at the end:
294
295            nbdkit data ' ( 0x55 0xAA ) -> \boot-signature
296                          ( @0x1fe \boot-signature ) -> \sector
297                          \sector \sector '
298
299       $VAR
300           (nbdkit ≥ 1.24)
301
302           Substitute command line parameters or environment variables.  The
303           variable is written in the same language as the "data" parameter,
304           and when substituted it creates a nested scope like "( ... )"
305           expressions.  These are all equivalent:
306
307            nbdkit data '$pattern*16' pattern='0x55 0xAA'
308
309            export pattern='0x55 0xAA'
310            nbdkit data '$pattern*16'
311
312            nbdkit data '( 0x55 0xAA )*16'
313
314       # COMMENT
315           (nbdkit ≥ 1.24)
316
317           "#" begins a comment stretching to the end of the current line.
318
319   disk2data.pl script
320       This script can convert from small disk images into the data format
321       described above.
322
323       It is provided in the nbdkit sources.  See
324       https://gitlab.com/nbdkit/nbdkit/blob/master/plugins/data/disk2data.pl
325

FILES

327       $plugindir/nbdkit-data-plugin.so
328           The plugin.
329
330           Use "nbdkit --dump-config" to find the location of $plugindir.
331

VERSION

333       "nbdkit-data-plugin" first appeared in nbdkit 1.6.
334

SEE ALSO

336       nbdkit(1), nbdkit-captive(1), nbdkit-plugin(3), nbdkit-info-plugin(1),
337       nbdkit-memory-plugin(1), nbdkit-null-plugin(1),
338       nbdkit-partitioning-plugin(1), nbdkit-pattern-plugin(1),
339       nbdkit-random-plugin(1), nbdkit-sparse-random-plugin(1),
340       nbdkit-tmpdisk-plugin(1), nbdkit-zero-plugin(1),
341       https://gitlab.com/nbdkit/nbdkit/blob/master/plugins/data/disk2data.pl,
342       https://en.wikipedia.org/wiki/Base64.
343

AUTHORS

345       Richard W.M. Jones
346
348       Copyright (C) 2018-2020 Red Hat Inc.
349

LICENSE

351       Redistribution and use in source and binary forms, with or without
352       modification, are permitted provided that the following conditions are
353       met:
354
355       •   Redistributions of source code must retain the above copyright
356           notice, this list of conditions and the following disclaimer.
357
358       •   Redistributions in binary form must reproduce the above copyright
359           notice, this list of conditions and the following disclaimer in the
360           documentation and/or other materials provided with the
361           distribution.
362
363       •   Neither the name of Red Hat nor the names of its contributors may
364           be used to endorse or promote products derived from this software
365           without specific prior written permission.
366
367       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
368       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
369       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
370       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
371       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
372       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
373       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
374       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
375       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
376       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
377       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
378
379
380
381nbdkit-1.28.2                     2021-11-09             nbdkit-data-plugin(1)
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