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nbdkit-nocache-filter(1)	    NBDKIT	      nbdkit-nocache-filter(1)

NAME
       nbdkit-nocache-filter - nbdkit nocache filter

SYNOPSIS
	nbdkit --filter=nocache	plugin [cachemode=MODE]	[plugin-args...]

DESCRIPTION
       "nbdkit-nocache-filter" is a filter that	intentionally disables
       efficient handling of advisory client cache requests across the NBD
       protocol.  It is	mainly useful for evaluating timing differences	to
       determine the impact of caching requests.

       Note that the effects of	this filter (in	crippling handling of client
       cache requests) is somewhat orthogonal from that	of the
       nbdkit-cache-filter(1) (adding local caching of client read/write
       requests); the two filters can be run together to experiment with
       timings.

PARAMETERS
       cachemode=none
       cachemode=emulate
       cachemode=nop
	   Optional, controls which mode the filter will use.  Mode none
	   (default) means that	cache support is not advertised	to the client.
	   Mode	emulate	means that cache support is emulated by	the filter
	   using the plugin's "pread" callback,	regardless of whether the
	   plugin itself implemented the "cache" callback. Mode	nop means that
	   cache requests are always accepted and immediately ignored, rather
	   than	having any actual impact.

EXAMPLES
       Serve the file disk.img,	but prevent "NBD_CMD_CACHE" requests
       altogether, to get a baseline timing of behavior	when the client	is
       unable to make cache requests:

	nbdkit --filter=nocache	file disk.img

       Serve the file disk.img,	but with cache requests	silently ignored,
       rather than being forwarded on to the file plugin (which	attempts to
       use posix_fadvise(3)), to compare against the timings without the
       filter and determine whether the	file plugin caching was	worthwhile:

	nbdkit --filter=nocache	file disk.img cachemode=nop

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

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

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

SEE ALSO
       nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3),
       nbdkit-cache-filter(1), nbdkit-fua-filter(1),
       nbdkit-noextents-filter(1), nbdkit-noparallel-filter(1),
       nbdkit-nozero-filter(1).

AUTHORS
       Eric Blake

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-nocache-filter(1)

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

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