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

6       nbdkit-nocache-filter - nbdkit nocache filter
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SYNOPSIS

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

12       "nbdkit-nocache-filter" is a filter that intentionally disables
13       efficient handling of advisory client cache requests across the NBD
14       protocol.  It is mainly useful for evaluating timing differences to
15       determine the impact of caching requests.
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17       Note that the effects of this filter (in crippling handling of client
18       cache requests) is somewhat orthogonal from that of the
19       nbdkit-cache-filter(1) (adding local caching of client read/write
20       requests); the two filters can be run together to experiment with
21       timings.
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PARAMETERS

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

36       Serve the file disk.img, but prevent "NBD_CMD_CACHE" requests
37       altogether, to get a baseline timing of behavior when the client is
38       unable to make cache requests:
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40        nbdkit --filter=nocache file disk.img
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42       Serve the file disk.img, but with cache requests silently ignored,
43       rather than being forwarded on to the file plugin (which attempts to
44       use posix_fadvise(3)), to compare against the timings without the
45       filter and determine whether the file plugin caching was worthwhile:
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47        nbdkit --filter=nocache file disk.img cachemode=nop
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FILES

50       $filterdir/nbdkit-nocache-filter.so
51           The filter.
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53           Use "nbdkit --dump-config" to find the location of $filterdir.
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VERSION

56       "nbdkit-nocache-filter" first appeared in nbdkit 1.14.
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SEE ALSO

59       nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3),
60       nbdkit-cache-filter(1), nbdkit-fua-filter(1),
61       nbdkit-noextents-filter(1), nbdkit-noparallel-filter(1),
62       nbdkit-nozero-filter(1).
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AUTHORS

65       Eric Blake
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68       Copyright (C) 2019 Red Hat Inc.
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LICENSE

71       Redistribution and use in source and binary forms, with or without
72       modification, are permitted provided that the following conditions are
73       met:
74
75       ·   Redistributions of source code must retain the above copyright
76           notice, this list of conditions and the following disclaimer.
77
78       ·   Redistributions in binary form must reproduce the above copyright
79           notice, this list of conditions and the following disclaimer in the
80           documentation and/or other materials provided with the
81           distribution.
82
83       ·   Neither the name of Red Hat nor the names of its contributors may
84           be used to endorse or promote products derived from this software
85           without specific prior written permission.
86
87       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
88       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
89       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
90       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
91       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
92       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
93       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
94       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
95       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
96       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
97       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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101nbdkit-1.16.1                     2019-12-03          nbdkit-nocache-filter(1)
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