1nbdkit-nozero-filter(1) NBDKIT nbdkit-nozero-filter(1)
2
6 nbdkit-nozero-filter - nbdkit nozero filter
7
9 nbdkit --filter=nozero plugin [plugin-args...] \
10 [zeromode=MODE] [fastzeromode=MODE]
11
13 "nbdkit-nozero-filter" is a filter that intentionally disables
14 efficient handling of sparse file holes (ranges of all-zero bytes)
15 across the NBD protocol. It is mainly useful for evaluating timing
16 differences between naive vs. sparse-aware connections, and for testing
17 client or server fallbacks.
18
20 zeromode=none
21 zeromode=emulate
22 zeromode=notrim
23 zeromode=plugin
24 Optional, controls which mode the filter will use. Mode none
25 (default) means that zero support is not advertised to the client.
26 Mode emulate means that zero support is emulated by the filter
27 using the plugin's "pwrite" callback, regardless of whether the
28 plugin itself implemented the "zero" callback with a more efficient
29 way to write zeros. Since nbdkit ≥ 1.13.4, mode notrim means that
30 zero requests are forwarded on to the plugin, except that the
31 plugin will never see the NBDKIT_MAY_TRIM flag, to determine if the
32 client permitting trimming during zero operations makes a
33 difference. Since nbdkit ≥ 1.15.0, mode plugin leaves normal zero
34 requests up to the plugin, useful when combined with "fastzeromode"
35 for experimenting with the effects of fast zero requests. It is an
36 error to request notrim or plugin if the plugin does not support
37 the "zero" callback.
38 fastzeromode=none
40 fastzeromode=slow
41 fastzeromode=ignore
42 fastzeromode=default
43 Optional since nbdkit ≥ 1.15.0, controls whether fast zeroes are
44 advertised to the client, and if so, how the filter will react to a
45 client fast zero request. Mode none avoids advertising fast zero
46 support. Mode slow advertises fast zero support unconditionally,
47 but treats all fast zero requests as an immediate "ENOTSUP" failure
48 rather than performing a fallback. Mode ignore advertises fast
49 zero support, but treats all client fast zero requests as if the
50 flag had not been used (this behavior is typically contrary to the
51 NBD specification, but can be useful for comparison against the
52 actual fast zero implementation to see if fast zeroes make a
53 difference). Mode default is selected by default; when paired with
54 "zeromode=emulate", fast zeroes are advertised but fast zero
55 requests always fail (similar to "slow"); when paired with
56 "zeromode=notrim" or "zeromode=plugin", fast zero support is left
57 to the plugin (although in the latter case, the nozero filter could
58 be omitted for the same behavior).
59
61 Serve the file disk.img, but force the client to write zeroes
62 explicitly rather than with "NBD_CMD_WRITE_ZEROES":
63 nbdkit --filter=nozero file disk.img
65 Serve the file disk.img, allowing the client to take advantage of less
67 network traffic via "NBD_CMD_WRITE_ZEROES", but fail any fast zero
68 requests up front and force all other zero requests to write data
69 explicitly rather than punching any holes:
70 nbdkit --filter=nozero file zeromode=emulate disk.img
72 Serve the file disk.img, but do not advertise fast zero support to the
74 client even if the plugin supports it:
75 nbdkit --filter=nozero file zeromode=plugin fastzeromode=none disk.img
77
79 $filterdir/nbdkit-nozero-filter.so
80 The filter.
81 Use "nbdkit --dump-config" to find the location of $filterdir.
83
85 "nbdkit-nozero-filter" first appeared in nbdkit 1.2.
86
88 nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3),
89 nbdkit-fua-filter(1), nbdkit-nocache-filter(1),
90 nbdkit-noparallel-filter(1), nbdkit-noextents-filter(1).
91
93 Eric Blake
94
96 Copyright (C) 2018-2019 Red Hat Inc.
97
99 Redistribution and use in source and binary forms, with or without
100 modification, are permitted provided that the following conditions are
101 met:
102 · Redistributions of source code must retain the above copyright
104 notice, this list of conditions and the following disclaimer.
105 · Redistributions in binary form must reproduce the above copyright
107 notice, this list of conditions and the following disclaimer in the
108 documentation and/or other materials provided with the
109 distribution.
110 · Neither the name of Red Hat nor the names of its contributors may
112 be used to endorse or promote products derived from this software
113 without specific prior written permission.
114 THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
116 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
117 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
118 PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
119 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
120 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
121 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
122 BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
123 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
124 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
125 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
126nbdkit-1.18.4 2020-04-16 nbdkit-nozero-filter(1)