1nbd_pwrite(3) LIBNBD nbd_pwrite(3)
2
6 nbd_pwrite - write to the NBD server
7
9 #include <libnbd.h>
10 int nbd_pwrite (struct nbd_handle *h, const void *buf,
12 size_t count, uint64_t offset,
13 uint32_t flags);
14
16 Issue a write command to the NBD server, writing the data in "buf" to
17 the range starting at "offset" and ending at "offset" + "count" - 1.
18 NBD can only write all or nothing using this call. The call returns
19 when the command has been acknowledged by the server, or there is an
20 error.
21 The "flags" parameter may be 0 for no flags, or may contain
23 "LIBNBD_CMD_FLAG_FUA" meaning that the server should not return until
24 the data has been committed to permanent storage (if that is supported
25 - some servers cannot do this, see nbd_can_fua(3)).
26
28 If the call is successful the function returns 0.
29
31 On error "-1" is returned.
32 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
34 of the error.
35
37 The handle must be connected and finished handshaking with the server,
38 otherwise this call will return an error.
39
41 This function first appeared in libnbd 1.0.
42 If you need to test if this function is available at compile time check
44 if the following macro is defined:
45 #define LIBNBD_HAVE_NBD_PWRITE 1
47
49 This example is also available as examples/reads-and-writes.c in the
50 libnbd source code.
51 /* This example shows how to do synchronous reads
53 * and writes randomly over the first megabyte of an
54 * NBD server. Note this will destroy any existing
55 * content on the NBD server.
56 *
57 * To test it with nbdkit and a RAM disk:
58 *
59 * nbdkit -U - memory 1M \
60 * --run './simple-reads-and-writes $unixsocket'
61 */
62 #include <stdio.h>
64 #include <stdlib.h>
65 #include <inttypes.h>
66 #include <assert.h>
67 #include <time.h>
68 #include <libnbd.h>
70 int
72 main (int argc, char *argv[])
73 {
74 struct nbd_handle *nbd;
75 char buf[512];
76 size_t i;
77 int64_t exportsize;
78 uint64_t offset;
79 srand (time (NULL));
81 if (argc != 2) {
83 fprintf (stderr, "%s socket\n", argv[0]);
84 exit (EXIT_FAILURE);
85 }
86 /* Create the libnbd handle. */
88 nbd = nbd_create ();
89 if (nbd == NULL) {
90 fprintf (stderr, "%s\n", nbd_get_error ());
91 exit (EXIT_FAILURE);
92 }
93 /* 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 /* Get the size of the disk and check
103 * it's large enough.
104 */
105 exportsize = nbd_get_size (nbd);
106 if (exportsize == -1) {
107 fprintf (stderr, "%s\n", nbd_get_error ());
108 exit (EXIT_FAILURE);
109 }
110 assert (exportsize >= sizeof buf);
111 /* Check that the server is writable. */
113 if (nbd_is_read_only (nbd) == 1) {
114 fprintf (stderr, "%s: "
115 "error: this NBD export is read-only\n",
116 argv[0]);
117 exit (EXIT_FAILURE);
118 }
119 for (i = 0; i < sizeof buf; ++i)
121 buf[i] = rand ();
122 /* 1000 writes. */
124 for (i = 0; i < 1000; ++i) {
125 offset = rand () % (exportsize - sizeof buf);
126 if (nbd_pwrite (nbd, buf, sizeof buf,
128 offset, 0) == -1) {
129 fprintf (stderr, "%s\n", nbd_get_error ());
130 exit (EXIT_FAILURE);
131 }
132 }
133 /* 1000 reads and writes. */
135 for (i = 0; i < 1000; ++i) {
136 offset = rand () % (exportsize - sizeof buf);
137 if (nbd_pread (nbd, buf, sizeof buf,
138 offset, 0) == -1) {
139 fprintf (stderr, "%s\n", nbd_get_error ());
140 exit (EXIT_FAILURE);
141 }
142 offset = rand () % (exportsize - sizeof buf);
144 if (nbd_pwrite (nbd, buf, sizeof buf,
145 offset, 0) == -1) {
146 fprintf (stderr, "%s\n", nbd_get_error ());
147 exit (EXIT_FAILURE);
148 }
149 }
150 /* Sends a graceful shutdown to the server. */
152 if (nbd_shutdown (nbd, 0) == -1) {
153 fprintf (stderr, "%s\n", nbd_get_error ());
154 exit (EXIT_FAILURE);
155 }
156 nbd_close (nbd);
158 exit (EXIT_SUCCESS);
160 }
161
163 nbd_can_fua(3), nbd_can_write(3), nbd_aio_pwrite(3), nbd_create(3),
164 libnbd(3).
165
167 Eric Blake
168 Richard W.M. Jones
170
172 Copyright (C) 2019 Red Hat Inc.
173
175 This library is free software; you can redistribute it and/or modify it
176 under the terms of the GNU Lesser General Public License as published
177 by the Free Software Foundation; either version 2 of the License, or
178 (at your option) any later version.
179 This library is distributed in the hope that it will be useful, but
181 WITHOUT ANY WARRANTY; without even the implied warranty of
182 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
183 Lesser General Public License for more details.
184 You should have received a copy of the GNU Lesser General Public
186 License along with this library; if not, write to the Free Software
187 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
188 02110-1301 USA
189libnbd-1.2.1 2019-11-14 nbd_pwrite(3)