1nbdkit-exportname-filter(1) NBDKIT nbdkit-exportname-filter(1)
2
6 nbdkit-exportname-filter - adjust export names between client and
7 plugin
8
10 nbdkit --filter=exportname plugin [default-export=NAME]
11 [exportname-list=MODE] [exportname-strict=true] [exportname=NAME]...
12 [exportdesc=DESC]
13
15 Some plugins (such as "nbdkit-file-plugin(1)" and filters (such as
16 "nbdkit-ext2-filter(1)" are able to serve different content based on
17 the export name requested by the client. The NBD protocol allows a
18 server to advertise the set of export names it is serving. However,
19 the list advertised (or absent) from the plugin may not always match
20 what you want an actual client to see. This filter can be used to
21 alter the advertised list, as well as configuring which export should
22 be treated as the default when the client requests the empty string
23 ("") as an export name.
24
26 default-export=NAME
27 When the client requests the default export name (""), request the
28 export "NAME" from the underlying plugin instead of relying on the
29 plugin's choice of default export. Setting NAME to the empty
30 string has the same effect as omitting this parameter.
31 exportname-list=keep
33 exportname-list=error
34 exportname-list=empty
35 exportname-list=defaultonly
36 exportname-list=explicit
37 This parameter determines which exports are advertised to a guest
38 that requests a listing via "NBD_OPT_LIST". The default mode is
39 "keep" to advertise whatever the underlying plugin reports. Mode
40 "error" causes clients to see an error rather than an export list.
41 Mode "empty" returns an empty list. Mode "defaultonly" returns a
42 list that contains only the canonical name of the default export.
43 Mode "explicit" returns only the exports set by "exportname=".
44 Note that the list of advertised exports need not reflect reality:
45 an advertised name may be rejected, or a client may connect to an
46 export name that was not advertised, but learned through other
47 means.
48 exportname-strict=false
50 exportname-strict=true
51 Normally, a client can pass whatever export name it wants,
52 regardless of whether that name is advertised. But setting this
53 parameter to true will cause the connection to fail if a client
54 requests an export name that was not included via an exportname=
55 parameter. At this time, it is not possible to restrict a client
56 to exports advertised by the plugin without repeating that list via
57 exportname; this technical limitation may be lifted in the future.
58 exportname=NAME
60 This parameter adds "NAME" to the list of advertised exports; it
61 may be set multiple times.
62 exportdesc=keep
64 exportdesc=none
65 exportdesc=fixed:STRING
66 exportdesc=script:SCRIPT
67 The "exportdesc" parameter controls what optional descriptions are
68 sent alongside an export name. If set to "keep" (the default),
69 descriptions are determined by the plugin. If set to "none",
70 descriptions from the plugin are ignored (useful if you are worried
71 about a potential information leak). If set to "fixed:STRING", the
72 same fixed string description is offered for every export. If set
73 to "script:SCRIPT", this filter executes script with $name set to
74 the export to be described, and uses the output of that command as
75 the description.
76
78 Suppose that the directory /path/to/dir contains permanent files named
79 file1, file2, and file3. The following commands show various ways to
80 alter the use of export names while serving that directory:
81 Allow a client requesting "" to get the contents of file2, rather than
83 an error:
84 nbdkit --filter=exportname file dir=/path/to/dir default-export=file2
86 Do not advertise any exports; a client must know in advance what export
88 names to try:
89 nbdkit --filter=exportname file dir=/path/to/dir exportname-list=empty
91 Allow clients to connect to file1 and file3, but not file2:
93 nbdkit --filter=exportname file dir=/path/to/dir \
95 exportname-list=explicit exportname-strict=true \
96 exportname=file1 exportname=file3
97 Offer ls(3) long descriptions alongside each export name:
99 nbdkit --filter=exportname file dir=/path/to/dir \
101 exportdesc=script:'ls -l /path/to/dir/"$name"'
102
104 $filterdir/nbdkit-exportname-filter.so
105 The filter.
106 Use "nbdkit --dump-config" to find the location of $filterdir.
108
110 "nbdkit-exportname-filter" first appeared in nbdkit 1.24.
111
113 nbdkit(1), nbdkit-filter(3), nbdkit-ext2-filter(1),
114 nbdkit-extentlist-filter(1), nbdkit-fua-filter(1),
115 nbdkit-nocache-filter(1), nbdkit-noparallel-filter(1),
116 nbdkit-nozero-filter(1), nbdkit-file-plugin(1), nbdkit-info-plugin(1).
117
119 Eric Blake
120
122 Copyright (C) 2020 Red Hat Inc.
123
125 Redistribution and use in source and binary forms, with or without
126 modification, are permitted provided that the following conditions are
127 met:
128 · Redistributions of source code must retain the above copyright
130 notice, this list of conditions and the following disclaimer.
131 · Redistributions in binary form must reproduce the above copyright
133 notice, this list of conditions and the following disclaimer in the
134 documentation and/or other materials provided with the
135 distribution.
136 · Neither the name of Red Hat nor the names of its contributors may
138 be used to endorse or promote products derived from this software
139 without specific prior written permission.
140 THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
142 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
143 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
144 PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
145 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
146 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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149 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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151 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
152nbdkit-1.24.2 2021-03-02 nbdkit-exportname-filter(1)