1nbdkit-blocksize-filter(1) NBDKIT nbdkit-blocksize-filter(1)
2
6 nbdkit-blocksize-filter - nbdkit blocksize filter
7
9 nbdkit --filter=blocksize plugin [minblock=SIZE] [maxdata=SIZE] \
10 [maxlen=SIZE] [plugin-args...]
11
13 "nbdkit-blocksize-filter" is a filter that ensures various block size
14 limits are met on transactions presented to the plugin. The NBD
15 protocol permits clients to send requests with a granularity as small
16 as 1 byte or as large as nearly 4 gigabytes, although it suggests that
17 portable clients should align requests to 512 bytes and not exceed 32
18 megabytes without prior coordination with the server.
19 Meanwhile, some plugins require requests to be aligned to 512-byte
21 multiples, or may enforce a maximum transaction size to bound the time
22 or memory resources spent by any one command (note that nbdkit itself
23 refuses a read or write larger than 64 megabytes, while many other NBD
24 servers limit things to 32 megabytes). The blocksize filter can be
25 used to modify the client requests to meet the plugin restrictions.
26
28 The nbdkit-blocksize-filter accepts the following parameters.
29 minblock=SIZE
31 The minimum block size and alignment to pass to the plugin. This
32 must be a power of two, and no larger than 64k. If omitted, this
33 defaults to 1 (that is, no minimum size restrictions). The filter
34 rounds up read requests to alignment boundaries, performs read-
35 modify-write cycles for any unaligned head or tail of a write or
36 zero request, and silently ignores any unaligned head or tail of a
37 trim request. The filter also truncates the plugin size down to an
38 aligned value (as it cannot safely operate on the unaligned tail);
39 it is an error if this would result in a size of 0.
40 This parameter understands the suffix 'k' for 1024.
42 maxdata=SIZE
44 The maximum block size for any single transaction with data (read
45 and write). If omitted, this defaults to 64 megabytes (that is,
46 the nbdkit maximum). This need not be a power of two, but must be
47 an integer multiple of "minblock". The filter fragments any larger
48 client request into multiple plugin requests.
49 This parameter understands the suffixes 'k', 'M', and 'G' for
51 powers of 1024.
52 maxlen=SIZE
54 The maximum length for any single transaction without data (trim,
55 zero or extents). If omitted, this defaults to 0xffffffff rounded
56 down to "minsize" alignment (that is, the inherent 32-bit limit of
57 the NBD protocol). This need not be a power of two, but must be an
58 integer multiple of "minblock", and should be at least as large as
59 "maxdata". The filter fragments any larger client request into
60 multiple plugin requests.
61 This parameter understands the suffixes 'k', 'M', and 'G' for
63 powers of 1024.
64
66 Allow an arbitrary client to use the VDDK plugin (which is limited to
67 512-byte blocks), without having to fix the client to avoid sending
68 unaligned requests:
69 nbdkit --filter=blocksize vddk minblock=512 file=/absolute/path/to/file.vmdk
71 Allow an arbitrary client tuned to nbdkit's 64 megabyte sizing to
73 connect to a remote server that insists on 32 megabyte sizing, via the
74 nbd plugin:
75 nbdkit --filter=blocksize nbd maxdata=32M socket=/path/to/socket
77
79 nbdkit(1), nbdkit-nbd-plugin(1), nbdkit-vddk-plugin(1),
80 nbdkit-filter(3).
81
83 Eric Blake
84
86 Copyright (C) 2018 Red Hat Inc.
87
89 Redistribution and use in source and binary forms, with or without
90 modification, are permitted provided that the following conditions are
91 met:
92 · Redistributions of source code must retain the above copyright
94 notice, this list of conditions and the following disclaimer.
95 · Redistributions in binary form must reproduce the above copyright
97 notice, this list of conditions and the following disclaimer in the
98 documentation and/or other materials provided with the
99 distribution.
100 · Neither the name of Red Hat nor the names of its contributors may
102 be used to endorse or promote products derived from this software
103 without specific prior written permission.
104 THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
106 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
107 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
108 PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
109 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
110 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
111 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
112 BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
113 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
114 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
115 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
116nbdkit-1.12.3 2019-05-22 nbdkit-blocksize-filter(1)