nbd_can_fast_zero(3)

1nbd_can_fast_zero(3)                LIBNBD                nbd_can_fast_zero(3)
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NAME

6       nbd_can_fast_zero - does the server support the fast zero flag?
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SYNOPSIS

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

DESCRIPTION

14       Returns true if the server supports the use of the
15       "LIBNBD_CMD_FLAG_FAST_ZERO" flag to the zero command (see nbd_zero(3),
16       nbd_aio_zero(3)).  Returns false if the server does not.
17
18       This call does not block, because it returns data that is saved in the
19       handle from the NBD protocol handshake.
20

RETURN VALUE

22       This call returns a boolean value.
23

ERRORS

25       On error "-1" is returned.
26
27       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
28       of the error.
29

HANDLE STATE

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

35       This function first appeared in libnbd 1.2.
36
37       If you need to test if this function is available at compile time check
38       if the following macro is defined:
39
40        #define LIBNBD_HAVE_NBD_CAN_FAST_ZERO 1
41

EXAMPLE

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

AUTHORS

143       Eric Blake
144
145       Richard W.M. Jones
146

COPYRIGHT

148       Copyright (C) 2019-2021 Red Hat Inc.
149

LICENSE

151       This library is free software; you can redistribute it and/or modify it
152       under the terms of the GNU Lesser General Public License as published
153       by the Free Software Foundation; either version 2 of the License, or
154       (at your option) any later version.
155
156       This library is distributed in the hope that it will be useful, but
157       WITHOUT ANY WARRANTY; without even the implied warranty of
158       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
159       Lesser General Public License for more details.
160
161       You should have received a copy of the GNU Lesser General Public
162       License along with this library; if not, write to the Free Software
163       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
164       02110-1301 USA
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168libnbd-1.10.1                     2021-10-25              nbd_can_fast_zero(3)