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 (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.
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RETURN VALUE

24       This call returns a boolean value.
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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

HANDLE STATE

33       The handle must be negotiating, or connected with the server, or shut
34       down, otherwise this call will return an error.
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VERSION

37       This function first appeared in libnbd 1.0.
38
39       If you need to test if this function is available at compile time check
40       if the following macro is defined:
41
42        #define LIBNBD_HAVE_NBD_CAN_DF 1
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EXAMPLE

45       This example is also available as examples/server-flags.c in the libnbd
46       source code.
47
48        /* This example shows how to connect to an NBD
49         * server and print the export flags.
50         *
51         * You can test it with nbdkit like this:
52         *
53         * nbdkit -U - memory 1M \
54         *   --run './server-flags $unixsocket'
55         */
56
57        #include <stdio.h>
58        #include <stdlib.h>
59
60        #include <libnbd.h>
61
62        int
63        main (int argc, char *argv[])
64        {
65          struct nbd_handle *nbd;
66          char *str;
67          int flag;
68
69          if (argc != 2) {
70            fprintf (stderr, "%s socket\n", argv[0]);
71            exit (EXIT_FAILURE);
72          }
73
74          /* Create the libnbd handle. */
75          nbd = nbd_create ();
76          if (nbd == NULL) {
77            fprintf (stderr, "%s\n", nbd_get_error ());
78            exit (EXIT_FAILURE);
79          }
80
81          /* Request full information. */
82        #if LIBNBD_HAVE_NBD_SET_FULL_INFO /* Added in 1.4 */
83          if (nbd_set_full_info (nbd, true) == -1) {
84            fprintf (stderr, "%s\n", nbd_get_error ());
85            exit (EXIT_FAILURE);
86          }
87        #endif
88
89          /* Connect to the NBD server over a
90           * Unix domain socket.
91           */
92          if (nbd_connect_unix (nbd, argv[1]) == -1) {
93            fprintf (stderr, "%s\n", nbd_get_error ());
94            exit (EXIT_FAILURE);
95          }
96
97          /* See if the server provided extra details,
98           * using functions added in 1.4
99           */
100        #if LIBNBD_HAVE_NBD_GET_EXPORT_DESCRIPTION
101          str = nbd_get_canonical_export_name (nbd);
102          if (str)
103            printf ("canonical_name = %s\n", str);
104          free (str);
105          str = nbd_get_export_description (nbd);
106          if (str)
107            printf ("description = %s\n", str);
108          free (str);
109        #endif
110
111          /* Read and print the flags. */
112        #define PRINT_FLAG(flag_fn)                     \
113          flag = flag_fn (nbd);                         \
114          if (flag == -1) {                             \
115            fprintf (stderr, "%s\n", nbd_get_error ()); \
116            exit (EXIT_FAILURE);                        \
117          }                                             \
118          printf (#flag_fn " = %s\n",                   \
119                  flag ? "true" : "false");
120
121          PRINT_FLAG (nbd_can_cache);
122          PRINT_FLAG (nbd_can_df);
123          PRINT_FLAG (nbd_can_flush);
124          PRINT_FLAG (nbd_can_fua);
125          PRINT_FLAG (nbd_can_multi_conn);
126          PRINT_FLAG (nbd_can_trim);
127          PRINT_FLAG (nbd_can_zero);
128        #if LIBNBD_HAVE_NBD_CAN_FAST_ZERO /* Added in 1.2 */
129          PRINT_FLAG (nbd_can_fast_zero);
130        #endif
131          PRINT_FLAG (nbd_is_read_only);
132          PRINT_FLAG (nbd_is_rotational);
133
134          /* Close the libnbd handle. */
135          nbd_close (nbd);
136
137          exit (EXIT_SUCCESS);
138        }
139

AUTHORS

145       Eric Blake
146
147       Richard W.M. Jones
148

COPYRIGHT

150       Copyright (C) 2019-2021 Red Hat Inc.
151

LICENSE

153       This library is free software; you can redistribute it and/or modify it
154       under the terms of the GNU Lesser General Public License as published
155       by the Free Software Foundation; either version 2 of the License, or
156       (at your option) any later version.
157
158       This library is distributed in the hope that it will be useful, but
159       WITHOUT ANY WARRANTY; without even the implied warranty of
160       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
161       Lesser General Public License for more details.
162
163       You should have received a copy of the GNU Lesser General Public
164       License along with this library; if not, write to the Free Software
165       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
166       02110-1301 USA
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170libnbd-1.7.12                     2021-05-29                     nbd_can_df(3)