1nbd_is_read_only(3) LIBNBD nbd_is_read_only(3)
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6 nbd_is_read_only - is the NBD export read-only?
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9 #include <libnbd.h>
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11 int nbd_is_read_only (struct nbd_handle *h);
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14 Returns true if the NBD export is read-only; writes and write-like
15 operations will fail.
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17 This call does not block, because it returns data that is saved in the
18 handle from the NBD protocol handshake.
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21 This call returns a boolean value.
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24 On error "-1" is returned.
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26 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
27 of the error.
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30 The handle must be connected and finished handshaking with the server,
31 or shut down, otherwise this call will return an error.
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34 This function first appeared in libnbd 1.0.
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36 If you need to test if this function is available at compile time check
37 if the following macro is defined:
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39 #define LIBNBD_HAVE_NBD_IS_READ_ONLY 1
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42 This example is also available as examples/server-flags.c in the libnbd
43 source code.
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45 /* This example shows how to connect to an NBD
46 * server and print the export flags.
47 *
48 * You can test it with nbdkit like this:
49 *
50 * nbdkit -U - memory 1M \
51 * --run './server-flags $unixsocket'
52 */
53
54 #include <stdio.h>
55 #include <stdlib.h>
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57 #include <libnbd.h>
58
59 int
60 main (int argc, char *argv[])
61 {
62 struct nbd_handle *nbd;
63 int flag;
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65 if (argc != 2) {
66 fprintf (stderr, "%s socket\n", argv[0]);
67 exit (EXIT_FAILURE);
68 }
69
70 /* Create the libnbd handle. */
71 nbd = nbd_create ();
72 if (nbd == NULL) {
73 fprintf (stderr, "%s\n", nbd_get_error ());
74 exit (EXIT_FAILURE);
75 }
76
77 /* Connect to the NBD server over a
78 * Unix domain socket.
79 */
80 if (nbd_connect_unix (nbd, argv[1]) == -1) {
81 fprintf (stderr, "%s\n", nbd_get_error ());
82 exit (EXIT_FAILURE);
83 }
84
85 /* Read and print the flags. */
86 #define PRINT_FLAG(flag_fn) \
87 flag = flag_fn (nbd); \
88 if (flag == -1) { \
89 fprintf (stderr, "%s\n", nbd_get_error ()); \
90 exit (EXIT_FAILURE); \
91 } \
92 printf (#flag_fn " = %s\n", \
93 flag ? "true" : "false");
94
95 PRINT_FLAG (nbd_can_cache);
96 PRINT_FLAG (nbd_can_df);
97 PRINT_FLAG (nbd_can_flush);
98 PRINT_FLAG (nbd_can_fua);
99 PRINT_FLAG (nbd_can_multi_conn);
100 PRINT_FLAG (nbd_can_trim);
101 PRINT_FLAG (nbd_can_zero);
102 #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
103 PRINT_FLAG (nbd_can_fast_zero);
104 #endif
105 PRINT_FLAG (nbd_is_read_only);
106 PRINT_FLAG (nbd_is_rotational);
107
108 /* Close the libnbd handle. */
109 nbd_close (nbd);
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111 exit (EXIT_SUCCESS);
112 }
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115 nbd_create(3), "Flag calls" in libnbd(3), libnbd(3).
116
118 Eric Blake
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120 Richard W.M. Jones
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123 Copyright (C) 2019 Red Hat Inc.
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126 This library is free software; you can redistribute it and/or modify it
127 under the terms of the GNU Lesser General Public License as published
128 by the Free Software Foundation; either version 2 of the License, or
129 (at your option) any later version.
130
131 This library is distributed in the hope that it will be useful, but
132 WITHOUT ANY WARRANTY; without even the implied warranty of
133 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
134 Lesser General Public License for more details.
135
136 You should have received a copy of the GNU Lesser General Public
137 License along with this library; if not, write to the Free Software
138 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
139 02110-1301 USA
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143libnbd-1.3.7 2020-04-23 nbd_is_read_only(3)