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:

• 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.
• 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:

• 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.