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-img 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:

       •   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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       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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