1nbdkit-checkwrite-filter(1)         NBDKIT         nbdkit-checkwrite-filter(1)
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NAME

6       nbdkit-checkwrite-filter - check writes match contents of plugin
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SYNOPSIS

9        nbdkit --filter=checkwrite PLUGIN
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DESCRIPTION

12       "nbdkit-checkwrite-filter" is an nbdkit filter that turns write
13       operations into checks that what is written matches the existing
14       content of the plugin.  If the content matches then the write operation
15       succeeds (doing nothing).  If not then the write operation fails
16       returning EIO Input/output error.
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18       The purpose of this filter is to test copying tools as described below.
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20       The underlying plugin is opened read-only and is never written to.  All
21       write-like operations are covered by this filter, such as trimming and
22       zeroing.  This filter tests the logical equivalence of the writes,
23       ignoring differences in sparseness.
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25   Using this filter to test copying tools
26       You can check that a copying tool is copying data correctly by creating
27       an nbdkit instance containing some test data, overlaying this filter,
28       and copying from and to nbdkit at the same time:
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30        nbdkit -U - --filter=checkwrite data "@32768 1" \
31               --run 'nbdcopy "$uri" "$uri"'
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33        nbdkit -U - --filter=checkwrite file disk.img \
34               --run 'nbdcopy "$uri" "$uri"'
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36        nbdkit -U - --filter=checkwrite linuxdisk testdir/ \
37               --run 'qemu-img convert -n "$uri" "$uri"'
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39       If the copying program is buggy then you will see EIO errors and (if
40       the copying program also handles errors correctly) it should exit with
41       an error.
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43   Other plugins for testing NBD tools
44       If you are doing this kind of testing you will also want to look at
45       nbdkit-random-plugin(1) and nbdkit-sparse-random-plugin(1).  These
46       plugins already have this behaviour built in to them (because it is
47       more efficient to build it into the plugin) — you do not need to use
48       this filter with those plugins.  This filter is useful for testing with
49       arbitrary plugins.
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PARAMETERS

52       There are no parameters specific to this filter.  Parameters are passed
53       through to the underlying plugin.
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FILES

56       $filterdir/nbdkit-checkwrite-filter.so
57           The filter.
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59           Use "nbdkit --dump-config" to find the location of $filterdir.
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VERSION

62       "nbdkit-checkwrite-filter" first appeared in nbdkit 1.24.
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SEE ALSO

65       nbdkit(1), nbdkit-random-plugin(1), nbdkit-sparse-random-plugin(1),
66       nbdkit-filter(3), nbdkit-plugin(3), nbdcopy(1), qemu-img(1).
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AUTHORS

69       Richard W.M. Jones
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72       Copyright Red Hat
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LICENSE

75       Redistribution and use in source and binary forms, with or without
76       modification, are permitted provided that the following conditions are
77       met:
78
79       •   Redistributions of source code must retain the above copyright
80           notice, this list of conditions and the following disclaimer.
81
82       •   Redistributions in binary form must reproduce the above copyright
83           notice, this list of conditions and the following disclaimer in the
84           documentation and/or other materials provided with the
85           distribution.
86
87       •   Neither the name of Red Hat nor the names of its contributors may
88           be used to endorse or promote products derived from this software
89           without specific prior written permission.
90
91       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
92       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
93       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
94       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
95       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
96       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
97       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
98       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
99       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
100       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
101       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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105nbdkit-1.34.4                     2023-09-26       nbdkit-checkwrite-filter(1)
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