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.\" ========================================================================
.\"
.IX Title "nbdkit-nocache-filter 1"
.TH nbdkit-nocache-filter 1 "2023-01-04" "nbdkit-1.32.5" "NBDKIT"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
nbdkit\-nocache\-filter \- nbdkit nocache filter
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=nocache plugin [cachemode=MODE] [plugin\-args...]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-nocache\-filter\*(C'\fR is a filter that intentionally disables
efficient handling of advisory client cache requests across the \s-1NBD\s0
protocol.  It is mainly useful for evaluating timing differences to
determine the impact of caching requests.
.PP
Note that the effects of this filter (in crippling handling of client
cache requests) is somewhat orthogonal from that of the
\&\fBnbdkit\-cache\-filter\fR\|(1) (adding local caching of client read/write
requests); the two filters can be run together to experiment with
timings.
.SH "PARAMETERS"
.IX Header "PARAMETERS"
.IP "\fBcachemode=none\fR" 4
.IX Item "cachemode=none"
.PD 0
.IP "\fBcachemode=emulate\fR" 4
.IX Item "cachemode=emulate"
.IP "\fBcachemode=nop\fR" 4
.IX Item "cachemode=nop"
.PD
Optional, controls which mode the filter will use.  Mode \fBnone\fR
(default) means that cache support is not advertised to the
client. Mode \fBemulate\fR means that cache support is emulated by the
filter using the plugin's \f(CW\*(C`pread\*(C'\fR callback, regardless of whether the
plugin itself implemented the \f(CW\*(C`cache\*(C'\fR callback. Mode \fBnop\fR means
that cache requests are always accepted and immediately ignored,
rather than having any actual impact.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Serve the file \fIdisk.img\fR, but prevent \f(CW\*(C`NBD_CMD_CACHE\*(C'\fR requests
altogether, to get a baseline timing of behavior when the client is
unable to make cache requests:
.PP
.Vb 1
\& nbdkit \-\-filter=nocache file disk.img
.Ve
.PP
Serve the file \fIdisk.img\fR, but with cache requests silently ignored,
rather than being forwarded on to the file plugin (which attempts to
use \fBposix_fadvise\fR\|(3)), to compare against the timings without the
filter and determine whether the file plugin caching was worthwhile:
.PP
.Vb 1
\& nbdkit \-\-filter=nocache file disk.img cachemode=nop
.Ve
.SH "FILES"
.IX Header "FILES"
.IP "\fI\f(CI$filterdir\fI/nbdkit\-nocache\-filter.so\fR" 4
.IX Item "$filterdir/nbdkit-nocache-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\-nocache\-filter\*(C'\fR first appeared in nbdkit 1.14.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-file\-plugin\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3),
\&\fBnbdkit\-cache\-filter\fR\|(1),
\&\fBnbdkit\-fua\-filter\fR\|(1),
\&\fBnbdkit\-multi\-conn\-filter\fR\|(1),
\&\fBnbdkit\-noextents\-filter\fR\|(1),
\&\fBnbdkit\-noparallel\-filter\fR\|(1),
\&\fBnbdkit\-nozero\-filter\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Eric Blake
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2019 Red Hat Inc.
.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
\&\s-1THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS\s0 ''\s-1AS IS\s0'' \s-1AND
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\s0 (\s-1INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES\s0; \s-1LOSS OF
USE, DATA, OR PROFITS\s0; \s-1OR BUSINESS INTERRUPTION\s0) \s-1HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT\s0 (\s-1INCLUDING NEGLIGENCE OR OTHERWISE\s0) \s-1ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.\s0