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.

nbdkit-1.42.2                                      2025-04-02                          nbdkit-readonly-filter(1)