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 (struct nbd_handle *h);
12

DESCRIPTION

14       Returns true if the server supports structured reads with an ability to
15       request a non-fragmented read (see nbd_pread_structured(3),
16       nbd_aio_pread_structured(3)).  Returns false if the server either lacks
17       structured reads or if it does not support a non-fragmented read
18       request.
19
20       This call does not block, because it returns data that is saved in the
21       handle from the NBD protocol handshake.
22

RETURN VALUE

24       This call returns a boolean value.
25

ERRORS

27       On error "-1" is returned.
28
29       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
30       of the error.
31

VERSION

33       This function first appeared in libnbd 1.0.
34
35       If you need to test if this function is available at compile time check
36       if the following macro is defined:
37
38        #define LIBNBD_HAVE_NBD_CAN_DF 1
39

EXAMPLE

41       This example is also available as examples/server-flags.c in the libnbd
42       source code.
43
44        /* This example shows how to connect to an NBD
45         * server and print the export flags.
46         *
47         * You can test it with nbdkit like this:
48         *
49         * nbdkit -U - memory 1M \
50         *   --run './server-flags $unixsocket'
51         */
52
53        #include <stdio.h>
54        #include <stdlib.h>
55
56        #include <libnbd.h>
57
58        int
59        main (int argc, char *argv[])
60        {
61          struct nbd_handle *nbd;
62          int flag;
63
64          if (argc != 2) {
65            fprintf (stderr, "%s socket\n", argv[0]);
66            exit (EXIT_FAILURE);
67          }
68
69          /* Create the libnbd handle. */
70          nbd = nbd_create ();
71          if (nbd == NULL) {
72            fprintf (stderr, "%s\n", nbd_get_error ());
73            exit (EXIT_FAILURE);
74          }
75
76          /* Connect to the NBD server over a
77           * Unix domain socket.
78           */
79          if (nbd_connect_unix (nbd, argv[1]) == -1) {
80            fprintf (stderr, "%s\n", nbd_get_error ());
81            exit (EXIT_FAILURE);
82          }
83
84          /* Read and print the flags. */
85        #define PRINT_FLAG(flag_fn)                     \
86          flag = flag_fn (nbd);                         \
87          if (flag == -1) {                             \
88            fprintf (stderr, "%s\n", nbd_get_error ()); \
89            exit (EXIT_FAILURE);                        \
90          }                                             \
91          printf (#flag_fn " = %s\n",                   \
92                  flag ? "true" : "false");
93
94          PRINT_FLAG (nbd_can_cache);
95          PRINT_FLAG (nbd_can_df);
96          PRINT_FLAG (nbd_can_flush);
97          PRINT_FLAG (nbd_can_fua);
98          PRINT_FLAG (nbd_can_multi_conn);
99          PRINT_FLAG (nbd_can_trim);
100          PRINT_FLAG (nbd_can_zero);
101        #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
102          PRINT_FLAG (nbd_can_fast_zero);
103        #endif
104          PRINT_FLAG (nbd_is_read_only);
105          PRINT_FLAG (nbd_is_rotational);
106
107          /* Close the libnbd handle. */
108          nbd_close (nbd);
109
110          exit (EXIT_SUCCESS);
111        }
112

SEE ALSO

114       nbd_aio_pread_structured(3), nbd_create(3), nbd_pread_structured(3),
115       "Flag calls" in libnbd(3), libnbd(3).
116

AUTHORS

118       Eric Blake
119
120       Richard W.M. Jones
121

123       Copyright (C) 2019 Red Hat Inc.
124

LICENSE

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_can_df(3)
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