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nbdkit-cacheextents-filter(1)	    NBDKIT	 nbdkit-cacheextents-filter(1)

NAME
       nbdkit-cacheextents-filter - cache extents

SYNOPSIS
	nbdkit --filter=cacheextents plugin

DESCRIPTION
       "nbdkit-cacheextents-filter" is a filter	that caches the	result of last
       extents() call.

       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 "qemu-imgA convert"),	but where the
       plugin can provide multiple extents for the same	high latency as	a
       single extent (such as nbdkit-vddk-plugin(1)).  For example:

	nbdkit -U - --filter=cacheextents --run	'qemu-img map $nbd' vddk ...

       For files with big extents (when	it is unlikely for one extents() call
       to return multiple different extents) this does not slow	down the
       access.

       This filter only	caches image metadata; to also cache image contents,
       place this filter between nbdkit-cache-filter(1)	and the	plugin.

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.

FILES
       $filterdir/nbdkit-cacheextents-filter.so
	   The filter.

	   Use "nbdkit --dump-config" to find the location of $filterdir.

VERSION
       "nbdkit-cacheextents-filter" first appeared in nbdkit 1.14.

SEE ALSO
       nbdkit(1), nbdkit-cache-filter(1), nbdkit-extentlist-filter(1),
       nbdkit-readahead-filter(1), nbdkit-vddk-plugin(1), nbdkit-filter(3),
       qemu-img(1).

AUTHORS
       Martin Kletzander

COPYRIGHT
       Copyright (C) 2019 Red Hat Inc.

LICENSE
       Redistribution and use in source	and binary forms, with or without
       modification, are permitted provided that the following conditions are
       met:

       o   Redistributions of source code must retain the above	copyright
	   notice, this	list of	conditions and the following disclaimer.

       o   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.

       o   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-1.20.4			  2021-09-21	 nbdkit-cacheextents-filter(1)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | FILES | VERSION | SEE ALSO | AUTHORS | COPYRIGHT | LICENSE

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