1nbd_add_meta_context(3) LIBNBD nbd_add_meta_context(3)
2
3
4
6 nbd_add_meta_context - ask server to negotiate metadata context
7
9 #include <libnbd.h>
10
11 int nbd_add_meta_context (struct nbd_handle *h,
12 const char *name);
13
15 During connection libnbd can negotiate zero or more metadata contexts
16 with the server. Metadata contexts are features (such as
17 "base:allocation") which describe information returned by the
18 nbd_block_status(3) command (for "base:allocation" this is whether
19 blocks of data are allocated, zero or sparse).
20
21 This call adds one metadata context to the list to be negotiated. You
22 can call it as many times as needed. The list is initially empty when
23 the handle is created; you can check the contents of the list with
24 nbd_get_nr_meta_contexts(3) and nbd_get_meta_context(3), or clear it
25 with nbd_clear_meta_contexts(3).
26
27 The NBD protocol limits meta context names to 4096 bytes, but servers
28 may not support the full length. The encoding of meta context names is
29 always UTF-8.
30
31 Not all servers support all metadata contexts. To learn if a context
32 was actually negotiated, call nbd_can_meta_context(3) after connecting.
33
34 The single parameter is the name of the metadata context, for example
35 "LIBNBD_CONTEXT_BASE_ALLOCATION". <libnbd.h> includes defined
36 constants beginning with "LIBNBD_CONTEXT_" for some well-known
37 contexts, but you are free to pass in other contexts.
38
39 Other metadata contexts are server-specific, but include
40 "qemu:dirty-bitmap:..." and "qemu:allocation-depth" for qemu-nbd (see
41 qemu-nbd -B and -A options).
42
44 If the call is successful the function returns 0.
45
47 On error "-1" is returned.
48
49 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
50 of the error.
51
52 The following parameters must not be NULL: "h", "name". For more
53 information see "Non-NULL parameters" in libnbd(3).
54
56 The handle must be newly created, or negotiating, otherwise this call
57 will return an error.
58
60 This function first appeared in libnbd 1.0.
61
62 If you need to test if this function is available at compile time check
63 if the following macro is defined:
64
65 #define LIBNBD_HAVE_NBD_ADD_META_CONTEXT 1
66
68 nbd_block_status(3), nbd_can_meta_context(3),
69 nbd_clear_meta_contexts(3), nbd_create(3), nbd_get_meta_context(3),
70 nbd_get_nr_meta_contexts(3), libnbd(3).
71
73 Eric Blake
74
75 Richard W.M. Jones
76
78 Copyright (C) 2019-2021 Red Hat Inc.
79
81 This library is free software; you can redistribute it and/or modify it
82 under the terms of the GNU Lesser General Public License as published
83 by the Free Software Foundation; either version 2 of the License, or
84 (at your option) any later version.
85
86 This library is distributed in the hope that it will be useful, but
87 WITHOUT ANY WARRANTY; without even the implied warranty of
88 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
89 Lesser General Public License for more details.
90
91 You should have received a copy of the GNU Lesser General Public
92 License along with this library; if not, write to the Free Software
93 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
94 02110-1301 USA
95
96
97
98libnbd-1.14.2 2023-01-03 nbd_add_meta_context(3)