NAME
nbdkit-checkwrite-filter - check writes match contents of plugin
SYNOPSIS
nbdkit --filter=checkwrite PLUGIN
DESCRIPTION
"nbdkit-checkwrite-filter" is an nbdkit filter that turns write operations into checks that what is written matches the existing content of the plugin. If the content matches then the write operation succeeds (doing nothing). If not then the write operation fails returning EIO Input/output error.
The purpose of this filter is to test copying tools as described below.
The underlying plugin is opened read-only and is never written to. All write-like operations are covered by this filter, such as trimming and zeroing. This filter tests the logical equivalence of the writes, ignoring differences in sparseness.
Using this
filter to test copying tools
You can check that a copying tool is copying data correctly
by creating an nbdkit instance containing some test data,
overlaying this filter, and copying from and to nbdkit at
the same time:
nbdkit
--filter=checkwrite data "@32768 1" \
--run 'nbdcopy "$uri" "$uri"'
nbdkit
--filter=checkwrite file disk.img \
--run 'nbdcopy "$uri" "$uri"'
nbdkit
--filter=checkwrite linuxdisk testdir/ \
--run 'qemu-img convert -n "$uri"
"$uri"'
If the copying program is buggy then you will see EIO errors and (if the copying program also handles errors correctly) it should exit with an error.
Other
plugins for testing NBD tools
If you are doing this kind of testing you will also want to
look at nbdkit-random-plugin(1) and
nbdkit-sparse-random-plugin(1). These plugins already
have this behaviour built in to them (because it is more
efficient to build it into the plugin) — you do
not need to use this filter with those plugins. This
filter is useful for testing with arbitrary plugins.
PARAMETERS
There are no parameters specific to this filter. Parameters are passed through to the underlying plugin.
FILES
$filterdir/nbdkit-checkwrite-filter.so
The filter.
Use "nbdkit --dump-config" to find the location of $filterdir.
VERSION
"nbdkit-checkwrite-filter" first appeared in nbdkit 1.24.
SEE ALSO
nbdkit(1), nbdkit-random-plugin(1), nbdkit-sparse-random-plugin(1), nbdkit-filter(3), nbdkit-plugin(3), nbdcopy(1), qemu-img(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:
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