1nbd_can_multi_conn(3) LIBNBD nbd_can_multi_conn(3)
2
6 nbd_can_multi_conn - does the server support multi-conn?
7
9 #include <libnbd.h>
10 int nbd_can_multi_conn (struct nbd_handle *h);
12
14 Returns true if the server supports multi-conn. Returns false if the
15 server does not.
16 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 This call does not block, because it returns data that is saved in the
24 handle from the NBD protocol handshake.
25
27 This call returns a boolean value.
28
30 On error "-1" is returned.
31 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
33 of the error.
34
36 The handle must be connected and finished handshaking with the server,
37 or shut down, otherwise this call will return an error.
38
40 This function first appeared in libnbd 1.0.
41 If you need to test if this function is available at compile time check
43 if the following macro is defined:
44 #define LIBNBD_HAVE_NBD_CAN_MULTI_CONN 1
46
48 This example is also available as examples/server-flags.c in the libnbd
49 source code.
50 /* This example shows how to connect to an NBD
52 * server and print the export flags.
53 *
54 * You can test it with nbdkit like this:
55 *
56 * nbdkit -U - memory 1M \
57 * --run './server-flags $unixsocket'
58 */
59 #include <stdio.h>
61 #include <stdlib.h>
62 #include <libnbd.h>
64 int
66 main (int argc, char *argv[])
67 {
68 struct nbd_handle *nbd;
69 int flag;
70 if (argc != 2) {
72 fprintf (stderr, "%s socket\n", argv[0]);
73 exit (EXIT_FAILURE);
74 }
75 /* Create the libnbd handle. */
77 nbd = nbd_create ();
78 if (nbd == NULL) {
79 fprintf (stderr, "%s\n", nbd_get_error ());
80 exit (EXIT_FAILURE);
81 }
82 /* Connect to the NBD server over a
84 * Unix domain socket.
85 */
86 if (nbd_connect_unix (nbd, argv[1]) == -1) {
87 fprintf (stderr, "%s\n", nbd_get_error ());
88 exit (EXIT_FAILURE);
89 }
90 /* Read and print the flags. */
92 #define PRINT_FLAG(flag_fn) \
93 flag = flag_fn (nbd); \
94 if (flag == -1) { \
95 fprintf (stderr, "%s\n", nbd_get_error ()); \
96 exit (EXIT_FAILURE); \
97 } \
98 printf (#flag_fn " = %s\n", \
99 flag ? "true" : "false");
100 PRINT_FLAG (nbd_can_cache);
102 PRINT_FLAG (nbd_can_df);
103 PRINT_FLAG (nbd_can_flush);
104 PRINT_FLAG (nbd_can_fua);
105 PRINT_FLAG (nbd_can_multi_conn);
106 PRINT_FLAG (nbd_can_trim);
107 PRINT_FLAG (nbd_can_zero);
108 #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
109 PRINT_FLAG (nbd_can_fast_zero);
110 #endif
111 PRINT_FLAG (nbd_is_read_only);
112 PRINT_FLAG (nbd_is_rotational);
113 /* Close the libnbd handle. */
115 nbd_close (nbd);
116 exit (EXIT_SUCCESS);
118 }
119
121 nbd_create(3), "Multi-conn" in libnbd(3), libnbd(3).
122
124 Eric Blake
125 Richard W.M. Jones
127
129 Copyright (C) 2019 Red Hat Inc.
130
132 This library is free software; you can redistribute it and/or modify it
133 under the terms of the GNU Lesser General Public License as published
134 by the Free Software Foundation; either version 2 of the License, or
135 (at your option) any later version.
136 This library is distributed in the hope that it will be useful, but
138 WITHOUT ANY WARRANTY; without even the implied warranty of
139 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
140 Lesser General Public License for more details.
141 You should have received a copy of the GNU Lesser General Public
143 License along with this library; if not, write to the Free Software
144 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
145 02110-1301 USA
146libnbd-1.3.7 2020-04-23 nbd_can_multi_conn(3)