1nbd_poll(3) LIBNBD nbd_poll(3)
2
6 nbd_poll - poll the handle once
7
9 #include <libnbd.h>
10 int nbd_poll (
12 struct nbd_handle *h, int timeout
13 );
14
16 This is a simple implementation of poll(2) which is used internally by
17 synchronous API calls. On success, it returns 0 if the "timeout" (in
18 milliseconds) occurs, or 1 if the poll completed and the state machine
19 progressed. Set "timeout" to -1 to block indefinitely (but be careful
20 that eventual action is actually expected - for example, if the
21 connection is established but there are no commands in flight, using an
22 infinite timeout will permanently block).
23 This function is mainly useful as an example of how you might integrate
25 libnbd with your own main loop, rather than being intended as something
26 you would use.
27
29 This call returns an integer ≥ 0.
30
32 On error -1 is returned.
33 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
35 of the error.
36 The following parameters must not be NULL: "h". For more information
38 see "Non-NULL parameters" in libnbd(3).
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_POLL 1
47
49 This example is also available as examples/aio-connect-read.c in the
50 libnbd source code.
51 /* This example shows how to use the AIO (asynchronous) low
53 * level API to connect to a server and read the disk.
54 *
55 * Here are a few ways to try this example:
56 *
57 * nbdkit -U - linuxdisk . \
58 * --run './aio-connect-read $unixsocket'
59 *
60 * nbdkit -U - floppy . \
61 * --run './aio-connect-read $unixsocket'
62 *
63 * nbdkit -U - pattern size=1M \
64 * --run './aio-connect-read $unixsocket'
65 */
66 #include <stdio.h>
68 #include <stdlib.h>
69 #include <stdint.h>
70 #include <inttypes.h>
71 #include <errno.h>
72 #include <assert.h>
73 #include <libnbd.h>
75 #define NR_SECTORS 32
77 #define SECTOR_SIZE 512
78 struct data {
80 uint64_t offset;
81 char sector[SECTOR_SIZE];
82 };
83 static int
85 hexdump (void *user_data, int *error)
86 {
87 struct data *data = user_data;
88 FILE *pp;
89 if (*error) {
91 errno = *error;
92 perror ("failed to read");
93 exit (EXIT_FAILURE);
94 }
95 printf ("sector at offset 0x%" PRIx64 ":\n",
97 data->offset);
98 pp = popen ("hexdump -C", "w");
99 if (pp == NULL) {
100 perror ("popen: hexdump");
101 exit (EXIT_FAILURE);
102 }
103 fwrite (data->sector, SECTOR_SIZE, 1, pp);
104 pclose (pp);
105 printf ("\n");
106 /* Returning 1 from the callback automatically retires
108 * the command.
109 */
110 return 1;
111 }
112 static struct data data[NR_SECTORS];
114 int
116 main (int argc, char *argv[])
117 {
118 struct nbd_handle *nbd;
119 size_t i;
120 if (argc != 2) {
122 fprintf (stderr, "%s socket\n", argv[0]);
123 exit (EXIT_FAILURE);
124 }
125 /* Create the libnbd handle. */
127 nbd = nbd_create ();
128 if (nbd == NULL) {
129 fprintf (stderr, "%s\n", nbd_get_error ());
130 exit (EXIT_FAILURE);
131 }
132 /* Connect to the NBD server over a Unix domain socket.
134 * This only starts the connection.
135 */
136 if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
137 fprintf (stderr, "%s\n", nbd_get_error ());
138 exit (EXIT_FAILURE);
139 }
140 /* Wait for the connection to complete. The use of
142 * nbd_poll here is only as an example. You could also
143 * integrate this with poll(2), glib or another main
144 * loop. Read libnbd(3) and the source file lib/poll.c.
145 */
146 while (!nbd_aio_is_ready (nbd)) {
147 if (nbd_poll (nbd, -1) == -1) {
148 fprintf (stderr, "%s\n", nbd_get_error ());
149 exit (EXIT_FAILURE);
150 }
151 }
152 assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
154 /* Issue read commands for the first NR sectors. */
156 for (i = 0; i < NR_SECTORS; ++i) {
157 data[i].offset = i * SECTOR_SIZE;
158 /* The callback (hexdump) is called when the command
160 * completes. The buffer must continue to exist while
161 * the command is running.
162 */
163 if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
164 data[i].offset,
165 (nbd_completion_callback) {
166 .callback = hexdump,
167 .user_data = &data[i],
168 }, 0) == -1) {
169 fprintf (stderr, "%s\n", nbd_get_error ());
170 exit (EXIT_FAILURE);
171 }
172 }
173 /* Run the main loop until all the commands have
175 * completed and retired. Again the use of nbd_poll
176 * here is only as an example.
177 */
178 while (nbd_aio_in_flight (nbd) > 0) {
179 if (nbd_poll (nbd, -1) == -1) {
180 fprintf (stderr, "%s\n", nbd_get_error ());
181 exit (EXIT_FAILURE);
182 }
183 }
184 /* Close the libnbd handle. */
186 nbd_close (nbd);
187 exit (EXIT_SUCCESS);
189 }
190
192 nbd_create(3), nbd_poll2(3), libnbd(3), poll(2).
193
195 Eric Blake
196 Richard W.M. Jones
198
200 Copyright Red Hat
201
203 This library is free software; you can redistribute it and/or modify it
204 under the terms of the GNU Lesser General Public License as published
205 by the Free Software Foundation; either version 2 of the License, or
206 (at your option) any later version.
207 This library is distributed in the hope that it will be useful, but
209 WITHOUT ANY WARRANTY; without even the implied warranty of
210 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
211 Lesser General Public License for more details.
212 You should have received a copy of the GNU Lesser General Public
214 License along with this library; if not, write to the Free Software
215 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
216 02110-1301 USA
217libnbd-1.18.1 2023-10-31 nbd_poll(3)