1nbd_can_df(3) LIBNBD nbd_can_df(3)
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6 nbd_can_df - does the server support the don't fragment flag to pread?
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9 #include <libnbd.h>
10
11 int nbd_can_df (
12 struct nbd_handle *h
13 );
14
16 Returns true if the server supports structured reads with an ability to
17 request a non-fragmented read (see nbd_pread_structured(3),
18 nbd_aio_pread_structured(3)). Returns false if the server either lacks
19 structured reads or if it does not support a non-fragmented read
20 request.
21
22 This call does not block, because it returns data that is saved in the
23 handle from the NBD protocol handshake.
24
26 This call returns a boolean value.
27
29 On error -1 is returned.
30
31 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
32 of the error.
33
34 The following parameters must not be NULL: "h". For more information
35 see "Non-NULL parameters" in libnbd(3).
36
38 The handle must be negotiating, or connected with the server, or shut
39 down, otherwise this call will return an error.
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42 This function first appeared in libnbd 1.0.
43
44 If you need to test if this function is available at compile time check
45 if the following macro is defined:
46
47 #define LIBNBD_HAVE_NBD_CAN_DF 1
48
50 This example is also available as examples/server-flags.c in the libnbd
51 source code.
52
53 /* This example shows how to connect to an NBD
54 * server and print the export flags.
55 *
56 * You can test it with nbdkit like this:
57 *
58 * nbdkit -U - memory 1M \
59 * --run './server-flags $unixsocket'
60 */
61
62 #include <stdio.h>
63 #include <stdlib.h>
64
65 #include <libnbd.h>
66
67 int
68 main (int argc, char *argv[])
69 {
70 struct nbd_handle *nbd;
71 char *str;
72 int flag;
73
74 if (argc != 2) {
75 fprintf (stderr, "%s socket\n", argv[0]);
76 exit (EXIT_FAILURE);
77 }
78
79 /* Create the libnbd handle. */
80 nbd = nbd_create ();
81 if (nbd == NULL) {
82 fprintf (stderr, "%s\n", nbd_get_error ());
83 exit (EXIT_FAILURE);
84 }
85
86 /* Request full information. */
87 #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
88 if (nbd_set_full_info (nbd, true) == -1) {
89 fprintf (stderr, "%s\n", nbd_get_error ());
90 exit (EXIT_FAILURE);
91 }
92 #endif
93
94 /* Connect to the NBD server over a
95 * Unix domain socket.
96 */
97 if (nbd_connect_unix (nbd, argv[1]) == -1) {
98 fprintf (stderr, "%s\n", nbd_get_error ());
99 exit (EXIT_FAILURE);
100 }
101
102 /* See if the server provided extra details,
103 * using functions added in 1.4
104 */
105 #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
106 str = nbd_get_canonical_export_name (nbd);
107 if (str)
108 printf ("canonical_name = %s\n", str);
109 free (str);
110 str = nbd_get_export_description (nbd);
111 if (str)
112 printf ("description = %s\n", str);
113 free (str);
114 #endif
115
116 /* Read and print the flags. */
117 #define PRINT_FLAG(flag_fn) \
118 flag = flag_fn (nbd); \
119 if (flag == -1) { \
120 fprintf (stderr, "%s\n", nbd_get_error ()); \
121 exit (EXIT_FAILURE); \
122 } \
123 printf (#flag_fn " = %s\n", \
124 flag ? "true" : "false");
125
126 PRINT_FLAG (nbd_can_cache);
127 PRINT_FLAG (nbd_can_df);
128 PRINT_FLAG (nbd_can_flush);
129 PRINT_FLAG (nbd_can_fua);
130 PRINT_FLAG (nbd_can_multi_conn);
131 PRINT_FLAG (nbd_can_trim);
132 PRINT_FLAG (nbd_can_zero);
133 #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO
134 /* Added in 1.2 */
135 PRINT_FLAG (nbd_can_fast_zero);
136 #endif
137 #if LIBNBD_HAVE_NBD_CAN_BLOCK_STATUS_PAYLOAD
138 /* Added in 1.18 */
139 PRINT_FLAG (nbd_can_block_status_payload);
140 #endif
141 PRINT_FLAG (nbd_is_read_only);
142 PRINT_FLAG (nbd_is_rotational);
143
144 /* Close the libnbd handle. */
145 nbd_close (nbd);
146
147 exit (EXIT_SUCCESS);
148 }
149
151 nbd_aio_pread_structured(3), nbd_create(3), nbd_opt_info(3),
152 nbd_pread_structured(3), "Flag calls" in libnbd(3), libnbd(3).
153
155 Eric Blake
156
157 Richard W.M. Jones
158
160 Copyright Red Hat
161
163 This library is free software; you can redistribute it and/or modify it
164 under the terms of the GNU Lesser General Public License as published
165 by the Free Software Foundation; either version 2 of the License, or
166 (at your option) any later version.
167
168 This library is distributed in the hope that it will be useful, but
169 WITHOUT ANY WARRANTY; without even the implied warranty of
170 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
171 Lesser General Public License for more details.
172
173 You should have received a copy of the GNU Lesser General Public
174 License along with this library; if not, write to the Free Software
175 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
176 02110-1301 USA
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179
180libnbd-1.18.1 2023-10-31 nbd_can_df(3)