1nbd_poll(3) LIBNBD nbd_poll(3)
2
6 nbd_poll - poll the handle once
7
9 #include <libnbd.h>
10 int nbd_poll (struct nbd_handle *h, int timeout);
12
14 This is a simple implementation of poll(2) which is used internally by
15 synchronous API calls. On success, it returns 0 if the "timeout" (in
16 milliseconds) occurs, or 1 if the poll completed and the state machine
17 progressed. Set "timeout" to "-1" to block indefinitely (but be careful
18 that eventual action is actually expected - for example, if the
19 connection is established but there are no commands in flight, using an
20 infinite timeout will permanently block).
21 This function is mainly useful as an example of how you might integrate
23 libnbd with your own main loop, rather than being intended as something
24 you would use.
25
27 This call returns an integer ≥ 0.
28
30 On error "-1" is returned.
31 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
33 of the error.
34 The following parameters must not be NULL: "h". For more information
36 see "Non-NULL parameters" in libnbd(3).
37
39 This function first appeared in libnbd 1.0.
40 If you need to test if this function is available at compile time check
42 if the following macro is defined:
43 #define LIBNBD_HAVE_NBD_POLL 1
45
47 This example is also available as examples/aio-connect-read.c in the
48 libnbd source code.
49 /* This example shows how to use the AIO (asynchronous) low
51 * level API to connect to a server and read the disk.
52 *
53 * Here are a few ways to try this example:
54 *
55 * nbdkit -U - linuxdisk . \
56 * --run './aio-connect-read $unixsocket'
57 *
58 * nbdkit -U - floppy . \
59 * --run './aio-connect-read $unixsocket'
60 *
61 * nbdkit -U - pattern size=1M \
62 * --run './aio-connect-read $unixsocket'
63 */
64 #include <stdio.h>
66 #include <stdlib.h>
67 #include <stdint.h>
68 #include <inttypes.h>
69 #include <errno.h>
70 #include <assert.h>
71 #include <libnbd.h>
73 #define NR_SECTORS 32
75 #define SECTOR_SIZE 512
76 struct data {
78 uint64_t offset;
79 char sector[SECTOR_SIZE];
80 };
81 static int
83 hexdump (void *user_data, int *error)
84 {
85 struct data *data = user_data;
86 FILE *pp;
87 if (*error) {
89 errno = *error;
90 perror ("failed to read");
91 exit (EXIT_FAILURE);
92 }
93 printf ("sector at offset 0x%" PRIx64 ":\n",
95 data->offset);
96 pp = popen ("hexdump -C", "w");
97 if (pp == NULL) {
98 perror ("popen: hexdump");
99 exit (EXIT_FAILURE);
100 }
101 fwrite (data->sector, SECTOR_SIZE, 1, pp);
102 pclose (pp);
103 printf ("\n");
104 /* Returning 1 from the callback automatically retires
106 * the command.
107 */
108 return 1;
109 }
110 static struct data data[NR_SECTORS];
112 int
114 main (int argc, char *argv[])
115 {
116 struct nbd_handle *nbd;
117 size_t i;
118 if (argc != 2) {
120 fprintf (stderr, "%s socket\n", argv[0]);
121 exit (EXIT_FAILURE);
122 }
123 /* Create the libnbd handle. */
125 nbd = nbd_create ();
126 if (nbd == NULL) {
127 fprintf (stderr, "%s\n", nbd_get_error ());
128 exit (EXIT_FAILURE);
129 }
130 /* Connect to the NBD server over a Unix domain socket.
132 * This only starts the connection.
133 */
134 if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
135 fprintf (stderr, "%s\n", nbd_get_error ());
136 exit (EXIT_FAILURE);
137 }
138 /* Wait for the connection to complete. The use of
140 * nbd_poll here is only as an example. You could also
141 * integrate this with poll(2), glib or another main
142 * loop. Read libnbd(3) and the source file lib/poll.c.
143 */
144 while (!nbd_aio_is_ready (nbd)) {
145 if (nbd_poll (nbd, -1) == -1) {
146 fprintf (stderr, "%s\n", nbd_get_error ());
147 exit (EXIT_FAILURE);
148 }
149 }
150 assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
152 /* Issue read commands for the first NR sectors. */
154 for (i = 0; i < NR_SECTORS; ++i) {
155 data[i].offset = i * SECTOR_SIZE;
156 /* The callback (hexdump) is called when the command
158 * completes. The buffer must continue to exist while
159 * the command is running.
160 */
161 if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
162 data[i].offset,
163 (nbd_completion_callback) {
164 .callback = hexdump,
165 .user_data = &data[i],
166 }, 0) == -1) {
167 fprintf (stderr, "%s\n", nbd_get_error ());
168 exit (EXIT_FAILURE);
169 }
170 }
171 /* Run the main loop until all the commands have
173 * completed and retired. Again the use of nbd_poll
174 * here is only as an example.
175 */
176 while (nbd_aio_in_flight (nbd) > 0) {
177 if (nbd_poll (nbd, -1) == -1) {
178 fprintf (stderr, "%s\n", nbd_get_error ());
179 exit (EXIT_FAILURE);
180 }
181 }
182 /* Close the libnbd handle. */
184 nbd_close (nbd);
185 exit (EXIT_SUCCESS);
187 }
188
190 nbd_create(3), libnbd(3), poll(2).
191
193 Eric Blake
194 Richard W.M. Jones
196
198 Copyright (C) 2019-2021 Red Hat Inc.
199
201 This library is free software; you can redistribute it and/or modify it
202 under the terms of the GNU Lesser General Public License as published
203 by the Free Software Foundation; either version 2 of the License, or
204 (at your option) any later version.
205 This library is distributed in the hope that it will be useful, but
207 WITHOUT ANY WARRANTY; without even the implied warranty of
208 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
209 Lesser General Public License for more details.
210 You should have received a copy of the GNU Lesser General Public
212 License along with this library; if not, write to the Free Software
213 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
214 02110-1301 USA
215libnbd-1.14.2 2023-01-03 nbd_poll(3)