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.

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