NAME
nbdkit-readonly-filter - switch a plugin between read-only and writable
SYNOPSIS
nbdkit
--filter=readonly PLUGIN
nbdkit --filter=readonly PLUGIN readonly-file=/tmp/ro
DESCRIPTION
"nbdkit-readonly-filter" is an nbdkit filter that has two modes:
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When the "readonly-file" parameter is not used, make the underlying plugin completely read-only. This is similar to using the nbdkit -r option on the command line. | ||
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When the "readonly-file" parameter is used, make the underlying plugin read-only when that file is present on disk, but leave it writable when the file is not present (or if the file is deleted). This way you can switch a plugin between being writable and write-protected at run time. |
Trying to write to the filter when the filter is enforcing read-only mode will cause "EPERM" ("Operation not permitted") to be returned to the client.
nbdkit-protect-filter(1) is a related filter which can write-protect parts of a plugin (eg only the boot sector). nbdkit-error-filter(1) is another filter which can be used for the same purpose as this filter but is more complicated to use. See also the -r option described in the nbdkit(1) manual.
EXAMPLE
Make a disk read-only 60 seconds after nbdkit is started:
rm -f /tmp/ro
nbdkit --filter=readonly file disk.img readonly-file=/tmp/ro
sleep 60; touch /tmp/ro
PARAMETERS
readonly-file=PATHNAME
If this parameter is used, the filter makes the underlying plugin read-only when PATHNAME exists, otherwise the plugin is writable as usual.
If this parameter is not used, the filter always makes the underlying plugin read-only.
FILES
$filterdir/nbdkit-readonly-filter.so
The filter.
Use "nbdkit --dump-config" to find the location of $filterdir.
VERSION
"nbdkit-readonly-filter" first appeared in nbdkit 1.38.
SEE ALSO
nbdkit(1), nbdkit-error-filter(1), nbdkit-file-plugin(1), nbdkit-full-plugin(1), nbdkit-protect-filter(1), nbdkit-filter(3).
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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Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. | ||
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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. | ||
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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. |
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