nbd_can_df(3)

1nbd_can_df(3)                       LIBNBD                       nbd_can_df(3)
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NAME

6       nbd_can_df - does the server support the don't fragment flag to pread?
7

SYNOPSIS

9        #include <libnbd.h>
10
11        int nbd_can_df (
12              struct nbd_handle *h
13            );
14

DESCRIPTION

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

RETURN VALUE

26       This call returns a boolean value.
27

ERRORS

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

HANDLE STATE

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

VERSION

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

EXAMPLE

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

AUTHORS

155       Eric Blake
156
157       Richard W.M. Jones
158

COPYRIGHT

160       Copyright Red Hat
161

LICENSE

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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180libnbd-1.18.1                     2023-10-31                     nbd_can_df(3)