1nbd_get_export_description(3) LIBNBD nbd_get_export_description(3)
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3
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6 nbd_get_export_description - return the export description, if the
7 server has one
8
10 #include <libnbd.h>
11
12 char * nbd_get_export_description (
13 struct nbd_handle *h
14 );
15
17 The NBD protocol permits a server to report an optional export
18 description. This function reports any description returned by the
19 server.
20
21 Some servers are unlikely to report a description unless the client
22 specifically hinted about wanting it, via nbd_set_full_info(3). For
23 qemu-nbd(8), a description is set with -D.
24
26 This call returns a string. The caller must free the returned string
27 to avoid a memory leak.
28
30 On error "NULL" is returned.
31
32 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
33 of the error.
34
35 The following parameters must not be NULL: "h". For more information
36 see "Non-NULL parameters" in libnbd(3).
37
39 The handle must be negotiating, or connected with the server, or shut
40 down, otherwise this call will return an error.
41
43 This function first appeared in libnbd 1.4.
44
45 If you need to test if this function is available at compile time check
46 if the following macro is defined:
47
48 #define LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION 1
49
51 This example is also available as examples/server-flags.c in the libnbd
52 source code.
53
54 /* This example shows how to connect to an NBD
55 * server and print the export flags.
56 *
57 * You can test it with nbdkit like this:
58 *
59 * nbdkit -U - memory 1M \
60 * --run './server-flags $unixsocket'
61 */
62
63 #include <stdio.h>
64 #include <stdlib.h>
65
66 #include <libnbd.h>
67
68 int
69 main (int argc, char *argv[])
70 {
71 struct nbd_handle *nbd;
72 char *str;
73 int flag;
74
75 if (argc != 2) {
76 fprintf (stderr, "%s socket\n", argv[0]);
77 exit (EXIT_FAILURE);
78 }
79
80 /* Create the libnbd handle. */
81 nbd = nbd_create ();
82 if (nbd == NULL) {
83 fprintf (stderr, "%s\n", nbd_get_error ());
84 exit (EXIT_FAILURE);
85 }
86
87 /* Request full information. */
88 #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
89 if (nbd_set_full_info (nbd, true) == -1) {
90 fprintf (stderr, "%s\n", nbd_get_error ());
91 exit (EXIT_FAILURE);
92 }
93 #endif
94
95 /* Connect to the NBD server over a
96 * Unix domain socket.
97 */
98 if (nbd_connect_unix (nbd, argv[1]) == -1) {
99 fprintf (stderr, "%s\n", nbd_get_error ());
100 exit (EXIT_FAILURE);
101 }
102
103 /* See if the server provided extra details,
104 * using functions added in 1.4
105 */
106 #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
107 str = nbd_get_canonical_export_name (nbd);
108 if (str)
109 printf ("canonical_name = %s\n", str);
110 free (str);
111 str = nbd_get_export_description (nbd);
112 if (str)
113 printf ("description = %s\n", str);
114 free (str);
115 #endif
116
117 /* Read and print the flags. */
118 #define PRINT_FLAG(flag_fn) \
119 flag = flag_fn (nbd); \
120 if (flag == -1) { \
121 fprintf (stderr, "%s\n", nbd_get_error ()); \
122 exit (EXIT_FAILURE); \
123 } \
124 printf (#flag_fn " = %s\n", \
125 flag ? "true" : "false");
126
127 PRINT_FLAG (nbd_can_cache);
128 PRINT_FLAG (nbd_can_df);
129 PRINT_FLAG (nbd_can_flush);
130 PRINT_FLAG (nbd_can_fua);
131 PRINT_FLAG (nbd_can_multi_conn);
132 PRINT_FLAG (nbd_can_trim);
133 PRINT_FLAG (nbd_can_zero);
134 #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO
135 /* Added in 1.2 */
136 PRINT_FLAG (nbd_can_fast_zero);
137 #endif
138 #if LIBNBD_HAVE_NBD_CAN_BLOCK_STATUS_PAYLOAD
139 /* Added in 1.18 */
140 PRINT_FLAG (nbd_can_block_status_payload);
141 #endif
142 PRINT_FLAG (nbd_is_read_only);
143 PRINT_FLAG (nbd_is_rotational);
144
145 /* Close the libnbd handle. */
146 nbd_close (nbd);
147
148 exit (EXIT_SUCCESS);
149 }
150
152 nbd_create(3), nbd_opt_info(3), nbd_set_full_info(3), libnbd(3).
153
155 Eric Blake
156
157 Richard W.M. Jones
158
160 Copyright Red Hat
161
163 This library is free software; you can redistribute it and/or modify it
164 under the terms of the GNU Lesser General Public License as published
165 by the Free Software Foundation; either version 2 of the License, or
166 (at your option) any later version.
167
168 This library is distributed in the hope that it will be useful, but
169 WITHOUT ANY WARRANTY; without even the implied warranty of
170 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
171 Lesser General Public License for more details.
172
173 You should have received a copy of the GNU Lesser General Public
174 License along with this library; if not, write to the Free Software
175 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
176 02110-1301 USA
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178
179
180libnbd-1.18.1 2023-10-31 nbd_get_export_description(3)