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

HANDLE STATE

34       The handle must be negotiating, or connected with the server, or shut
35       down, otherwise this call will return an error.
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VERSION

38       This function first appeared in libnbd 1.4.
39
40       If you need to test if this function is available at compile time check
41       if the following macro is defined:
42
43        #define LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION 1
44

EXAMPLE

46       This example is also available as examples/server-flags.c in the libnbd
47       source code.
48
49        /* This example shows how to connect to an NBD
50         * server and print the export flags.
51         *
52         * You can test it with nbdkit like this:
53         *
54         * nbdkit -U - memory 1M \
55         *   --run './server-flags $unixsocket'
56         */
57
58        #include <stdio.h>
59        #include <stdlib.h>
60
61        #include <libnbd.h>
62
63        int
64        main (int argc, char *argv[])
65        {
66          struct nbd_handle *nbd;
67          char *str;
68          int flag;
69
70          if (argc != 2) {
71            fprintf (stderr, "%s socket\n", argv[0]);
72            exit (EXIT_FAILURE);
73          }
74
75          /* Create the libnbd handle. */
76          nbd = nbd_create ();
77          if (nbd == NULL) {
78            fprintf (stderr, "%s\n", nbd_get_error ());
79            exit (EXIT_FAILURE);
80          }
81
82          /* Request full information. */
83        #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
84          if (nbd_set_full_info (nbd, true) == -1) {
85            fprintf (stderr, "%s\n", nbd_get_error ());
86            exit (EXIT_FAILURE);
87          }
88        #endif
89
90          /* Connect to the NBD server over a
91           * Unix domain socket.
92           */
93          if (nbd_connect_unix (nbd, argv[1]) == -1) {
94            fprintf (stderr, "%s\n", nbd_get_error ());
95            exit (EXIT_FAILURE);
96          }
97
98          /* See if the server provided extra details,
99           * using functions added in 1.4
100           */
101        #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
102          str = nbd_get_canonical_export_name (nbd);
103          if (str)
104            printf ("canonical_name = %s\n", str);
105          free (str);
106          str = nbd_get_export_description (nbd);
107          if (str)
108            printf ("description = %s\n", str);
109          free (str);
110        #endif
111
112          /* Read and print the flags. */
113        #define PRINT_FLAG(flag_fn)                     \
114          flag = flag_fn (nbd);                         \
115          if (flag == -1) {                             \
116            fprintf (stderr, "%s\n", nbd_get_error ()); \
117            exit (EXIT_FAILURE);                        \
118          }                                             \
119          printf (#flag_fn " = %s\n",                   \
120                  flag ? "true" : "false");
121
122          PRINT_FLAG (nbd_can_cache);
123          PRINT_FLAG (nbd_can_df);
124          PRINT_FLAG (nbd_can_flush);
125          PRINT_FLAG (nbd_can_fua);
126          PRINT_FLAG (nbd_can_multi_conn);
127          PRINT_FLAG (nbd_can_trim);
128          PRINT_FLAG (nbd_can_zero);
129        #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
130          PRINT_FLAG (nbd_can_fast_zero);
131        #endif
132          PRINT_FLAG (nbd_is_read_only);
133          PRINT_FLAG (nbd_is_rotational);
134
135          /* Close the libnbd handle. */
136          nbd_close (nbd);
137
138          exit (EXIT_SUCCESS);
139        }
140

AUTHORS

145       Eric Blake
146
147       Richard W.M. Jones
148

COPYRIGHT

150       Copyright (C) 2019-2021 Red Hat Inc.
151

LICENSE

153       This library is free software; you can redistribute it and/or modify it
154       under the terms of the GNU Lesser General Public License as published
155       by the Free Software Foundation; either version 2 of the License, or
156       (at your option) any later version.
157
158       This library is distributed in the hope that it will be useful, but
159       WITHOUT ANY WARRANTY; without even the implied warranty of
160       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
161       Lesser General Public License for more details.
162
163       You should have received a copy of the GNU Lesser General Public
164       License along with this library; if not, write to the Free Software
165       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
166       02110-1301 USA
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170libnbd-1.7.12                     2021-05-29     nbd_get_export_description(3)