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.IX Title "nbdkit-openonce-filter 1"
.TH nbdkit-openonce-filter 1 2026-07-14 nbdkit-1.48.0 NBDKIT
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.SH NAME
nbdkit\-openonce\-filter \- open the underlying plugin once
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=openonce PLUGIN
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-openonce\-filter\*(C'\fR is a filter for \fBnbdkit\fR\|(1) that opens the
underlying plugin once (per export).  This can be used if the plugin
is slow to open/connect (such as \fBnbdkit\-ssh\-plugin\fR\|(1) or
\&\fBnbdkit\-vddk\-plugin\fR\|(1)).
.PP
Some disadvantages are:
.IP \(bu 4
Multiple NBD clients may be sharing one connection to the plugin which
might cause performance issues.
.IP \(bu 4
The plugin stays open until nbdkit shuts down.
.IP \(bu 4
This defeats multi\-conn.  If nbdkit advertises multi\-conn, NBD clients
may make multiple connections but will end up connecting to the same
underlying plugin instance.  (See also
\&\fBnbdkit\-multi\-conn\-filter\fR\|(1)).
.SH PARAMETERS
.IX Header "PARAMETERS"
There are no parameters specific to nbdkit\-openonce\-filter.  Any
parameters are passed through to and processed by the underlying
plugin in the normal way.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-openonce\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-openonce\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-openonce-filter.so"
The filter.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$filterdir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-openonce\-filter\*(C'\fR first appeared in nbdkit 1.44.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-cache\-filter\fR\|(1),
\&\fBnbdkit\-multi\-conn\-filter\fR\|(1),
\&\fBnbdkit\-retry\-filter\fR\|(1),
\&\fBnbdkit\-curl\-plugin\fR\|(1),
\&\fBnbdkit\-ssh\-plugin\fR\|(1),
\&\fBnbdkit\-vddk\-plugin\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
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.
.IP \(bu 4
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.
.PP
THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \*(Aq\*(AqAS IS\*(Aq\*(Aq 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.
