nbd_can_multi_conn(3)

1nbd_can_multi_conn(3)               LIBNBD               nbd_can_multi_conn(3)
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NAME

6       nbd_can_multi_conn - does the server support multi-conn?
7

SYNOPSIS

9        #include <libnbd.h>
10
11        int nbd_can_multi_conn (struct nbd_handle *h);
12

DESCRIPTION

14       Returns true if the server supports multi-conn.  Returns false if the
15       server does not.
16
17       It is not safe to open multiple handles connecting to the same server
18       if you will write to the server and the server does not advertise
19       multi-conn support.  The safe way to check for this is to open one
20       connection, check this flag is true, then open further connections as
21       required.
22
23       This call does not block, because it returns data that is saved in the
24       handle from the NBD protocol handshake.
25

RETURN VALUE

27       This call returns a boolean value.
28

ERRORS

30       On error "-1" 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

HANDLE STATE

39       The handle must be negotiating, or connected with the server, or shut
40       down, otherwise this call will return an error.
41

VERSION

43       This function first appeared in libnbd 1.0.
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_CAN_MULTI_CONN 1
49

EXAMPLE

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 /* Added in 1.2 */
135          PRINT_FLAG (nbd_can_fast_zero);
136        #endif
137          PRINT_FLAG (nbd_is_read_only);
138          PRINT_FLAG (nbd_is_rotational);
139
140          /* Close the libnbd handle. */
141          nbd_close (nbd);
142
143          exit (EXIT_SUCCESS);
144        }
145

AUTHORS

151       Eric Blake
152
153       Richard W.M. Jones
154

COPYRIGHT

156       Copyright (C) 2019-2021 Red Hat Inc.
157

LICENSE

159       This library is free software; you can redistribute it and/or modify it
160       under the terms of the GNU Lesser General Public License as published
161       by the Free Software Foundation; either version 2 of the License, or
162       (at your option) any later version.
163
164       This library is distributed in the hope that it will be useful, but
165       WITHOUT ANY WARRANTY; without even the implied warranty of
166       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
167       Lesser General Public License for more details.
168
169       You should have received a copy of the GNU Lesser General Public
170       License along with this library; if not, write to the Free Software
171       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
172       02110-1301 USA
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176libnbd-1.14.2                     2023-01-03             nbd_can_multi_conn(3)