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.IX Title "nbdkit-cacheextents-filter 1"
.TH nbdkit-cacheextents-filter 1 2024-01-17 nbdkit-1.36.3 NBDKIT
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
nbdkit\-cacheextents\-filter \- cache extents
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=cacheextents plugin
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-cacheextents\-filter\*(C'\fR is a filter that caches the result of last
\&\fBextents()\fR call.
.PP
A common use for this filter is to improve performance when using a
client performing a linear pass over the entire image while asking for
only one extent at a time (such as \f(CW\*(C`qemu\-img\ convert\*(C'\fR), but where
the plugin can provide multiple extents for the same high latency as a
single extent (such as \fBnbdkit\-vddk\-plugin\fR\|(1)).  For example:
.PP
.Vb 1
\& nbdkit \-\-filter=cacheextents \-\-run \*(Aqqemu\-img map $nbd\*(Aq vddk ...
.Ve
.PP
For files with big extents (when it is unlikely for one \fBextents()\fR call
to return multiple different extents) this does not slow down the
access.
.PP
This filter only caches image metadata; to also cache image contents,
place this filter between \fBnbdkit\-cache\-filter\fR\|(1) and the plugin.
.SH PARAMETERS
.IX Header "PARAMETERS"
There are no parameters specific to nbdkit-cacheextents-filter.  Any
parameters are passed through to and processed by the underlying
plugin in the normal way.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-cacheextents\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-cacheextents\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-cacheextents-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\-cacheextents\-filter\*(C'\fR first appeared in nbdkit 1.14.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-cache\-filter\fR\|(1),
\&\fBnbdkit\-extentlist\-filter\fR\|(1),
\&\fBnbdkit\-readahead\-filter\fR\|(1),
\&\fBnbdkit\-scan\-filter\fR\|(1),
\&\fBnbdkit\-vddk\-plugin\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3),
\&\fBqemu\-img\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Martin Kletzander
.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 ''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.