nbd_get_export_description(3)

1nbd_get_export_description(3)       LIBNBD       nbd_get_export_description(3)
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NAME

6       nbd_get_export_description - return the export description, if the
7       server has one
8

SYNOPSIS

10        #include <libnbd.h>
11
12        char * nbd_get_export_description (struct nbd_handle *h);
13

DESCRIPTION

15       The NBD protocol permits a server to report an optional export
16       description.  This function reports any description returned by the
17       server.
18
19       Some servers are unlikely to report a description unless the client
20       specifically hinted about wanting it, via nbd_set_full_info(3).  For
21       qemu-nbd(8), a description is set with -D.
22

RETURN VALUE

24       This call returns a string.  The caller must free the returned string
25       to avoid a memory leak.
26

ERRORS

28       On error "NULL" is returned.
29
30       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
31       of the error.
32
33       The following parameters must not be NULL: "h".  For more information
34       see "Non-NULL parameters" in libnbd(3).
35

HANDLE STATE

37       The handle must be negotiating, or connected with the server, or shut
38       down, otherwise this call will return an error.
39

VERSION

41       This function first appeared in libnbd 1.4.
42
43       If you need to test if this function is available at compile time check
44       if the following macro is defined:
45
46        #define LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION 1
47

EXAMPLE

49       This example is also available as examples/server-flags.c in the libnbd
50       source code.
51
52        /* This example shows how to connect to an NBD
53         * server and print the export flags.
54         *
55         * You can test it with nbdkit like this:
56         *
57         * nbdkit -U - memory 1M \
58         *   --run './server-flags $unixsocket'
59         */
60
61        #include <stdio.h>
62        #include <stdlib.h>
63
64        #include <libnbd.h>
65
66        int
67        main (int argc, char *argv[])
68        {
69          struct nbd_handle *nbd;
70          char *str;
71          int flag;
72
73          if (argc != 2) {
74            fprintf (stderr, "%s socket\n", argv[0]);
75            exit (EXIT_FAILURE);
76          }
77
78          /* Create the libnbd handle. */
79          nbd = nbd_create ();
80          if (nbd == NULL) {
81            fprintf (stderr, "%s\n", nbd_get_error ());
82            exit (EXIT_FAILURE);
83          }
84
85          /* Request full information. */
86        #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
87          if (nbd_set_full_info (nbd, true) == -1) {
88            fprintf (stderr, "%s\n", nbd_get_error ());
89            exit (EXIT_FAILURE);
90          }
91        #endif
92
93          /* Connect to the NBD server over a
94           * Unix domain socket.
95           */
96          if (nbd_connect_unix (nbd, argv[1]) == -1) {
97            fprintf (stderr, "%s\n", nbd_get_error ());
98            exit (EXIT_FAILURE);
99          }
100
101          /* See if the server provided extra details,
102           * using functions added in 1.4
103           */
104        #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
105          str = nbd_get_canonical_export_name (nbd);
106          if (str)
107            printf ("canonical_name = %s\n", str);
108          free (str);
109          str = nbd_get_export_description (nbd);
110          if (str)
111            printf ("description = %s\n", str);
112          free (str);
113        #endif
114
115          /* Read and print the flags. */
116        #define PRINT_FLAG(flag_fn)                     \
117          flag = flag_fn (nbd);                         \
118          if (flag == -1) {                             \
119            fprintf (stderr, "%s\n", nbd_get_error ()); \
120            exit (EXIT_FAILURE);                        \
121          }                                             \
122          printf (#flag_fn " = %s\n",                   \
123                  flag ? "true" : "false");
124
125          PRINT_FLAG (nbd_can_cache);
126          PRINT_FLAG (nbd_can_df);
127          PRINT_FLAG (nbd_can_flush);
128          PRINT_FLAG (nbd_can_fua);
129          PRINT_FLAG (nbd_can_multi_conn);
130          PRINT_FLAG (nbd_can_trim);
131          PRINT_FLAG (nbd_can_zero);
132        #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
133          PRINT_FLAG (nbd_can_fast_zero);
134        #endif
135          PRINT_FLAG (nbd_is_read_only);
136          PRINT_FLAG (nbd_is_rotational);
137
138          /* Close the libnbd handle. */
139          nbd_close (nbd);
140
141          exit (EXIT_SUCCESS);
142        }
143

AUTHORS

148       Eric Blake
149
150       Richard W.M. Jones
151

COPYRIGHT

153       Copyright (C) 2019-2021 Red Hat Inc.
154

LICENSE

156       This library is free software; you can redistribute it and/or modify it
157       under the terms of the GNU Lesser General Public License as published
158       by the Free Software Foundation; either version 2 of the License, or
159       (at your option) any later version.
160
161       This library is distributed in the hope that it will be useful, but
162       WITHOUT ANY WARRANTY; without even the implied warranty of
163       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
164       Lesser General Public License for more details.
165
166       You should have received a copy of the GNU Lesser General Public
167       License along with this library; if not, write to the Free Software
168       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
169       02110-1301 USA
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171
172
173libnbd-1.14.2                     2023-01-03     nbd_get_export_description(3)