1nbd_aio_connect_unix(3) LIBNBD nbd_aio_connect_unix(3)
2
6 nbd_aio_connect_unix - connect to the NBD server over a Unix domain
7 socket
8
10 #include <libnbd.h>
11 int nbd_aio_connect_unix (struct nbd_handle *h,
13 const char *unixsocket);
14
16 Begin connecting to the NBD server over Unix domain socket
17 ("unixsocket"). Parameters behave as documented in
18 nbd_connect_unix(3).
19 You can check if the connection is still connecting by calling
21 nbd_aio_is_connecting(3), or if it has connected to the server and
22 completed the NBD handshake by calling nbd_aio_is_ready(3), on the
23 connection.
24
26 If the call is successful the function returns 0.
27
29 On error "-1" is returned.
30 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
32 of the error.
33
35 The handle must be newly created, otherwise this call will return an
36 error.
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_AIO_CONNECT_UNIX 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 <assert.h>
70 #include <libnbd.h>
72 #define NR_SECTORS 32
74 #define SECTOR_SIZE 512
75 struct data {
77 uint64_t offset;
78 char sector[SECTOR_SIZE];
79 };
80 static int
82 hexdump (void *user_data, int *error)
83 {
84 struct data *data = user_data;
85 FILE *pp;
86 printf ("sector at offset 0x%" PRIx64 ":\n",
88 data->offset);
89 pp = popen ("hexdump -C", "w");
90 if (pp == NULL) {
91 perror ("popen: hexdump");
92 exit (EXIT_FAILURE);
93 }
94 fwrite (data->sector, SECTOR_SIZE, 1, pp);
95 pclose (pp);
96 printf ("\n");
97 /* Returning 1 from the callback automatically retires
99 * the command.
100 */
101 return 1;
102 }
103 static struct data data[NR_SECTORS];
105 int
107 main (int argc, char *argv[])
108 {
109 struct nbd_handle *nbd;
110 size_t i;
111 if (argc != 2) {
113 fprintf (stderr, "%s socket\n", argv[0]);
114 exit (EXIT_FAILURE);
115 }
116 /* Create the libnbd handle. */
118 nbd = nbd_create ();
119 if (nbd == NULL) {
120 fprintf (stderr, "%s\n", nbd_get_error ());
121 exit (EXIT_FAILURE);
122 }
123 /* Connect to the NBD server over a Unix domain socket.
125 * This only starts the connection.
126 */
127 if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
128 fprintf (stderr, "%s\n", nbd_get_error ());
129 exit (EXIT_FAILURE);
130 }
131 /* Wait for the connection to complete. The use of
133 * nbd_poll here is only as an example. You could also
134 * integrate this with poll(2), glib or another main
135 * loop. Read libnbd(3) and the source file lib/poll.c.
136 */
137 while (!nbd_aio_is_ready (nbd)) {
138 if (nbd_poll (nbd, -1) == -1) {
139 fprintf (stderr, "%s\n", nbd_get_error ());
140 exit (EXIT_FAILURE);
141 }
142 }
143 assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
145 /* Issue read commands for the first NR sectors. */
147 for (i = 0; i < NR_SECTORS; ++i) {
148 data[i].offset = i * SECTOR_SIZE;
149 /* The callback (hexdump) is called when the command
151 * completes. The buffer must continue to exist while
152 * the command is running.
153 */
154 if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
155 data[i].offset,
156 (nbd_completion_callback) {
157 .callback = hexdump,
158 .user_data = &data[i],
159 }, 0) == -1) {
160 fprintf (stderr, "%s\n", nbd_get_error ());
161 exit (EXIT_FAILURE);
162 }
163 }
164 /* Run the main loop until all the commands have
166 * completed and retired. Again the use of nbd_poll
167 * here is only as an example.
168 */
169 while (nbd_aio_in_flight (nbd) > 0) {
170 if (nbd_poll (nbd, -1) == -1) {
171 fprintf (stderr, "%s\n", nbd_get_error ());
172 exit (EXIT_FAILURE);
173 }
174 }
175 /* Close the libnbd handle. */
177 nbd_close (nbd);
178 exit (EXIT_SUCCESS);
180 }
181
183 nbd_aio_is_connecting(3), nbd_aio_is_ready(3), nbd_connect_unix(3),
184 nbd_create(3), libnbd(3).
185
187 Eric Blake
188 Richard W.M. Jones
190
192 Copyright (C) 2019-2021 Red Hat Inc.
193
195 This library is free software; you can redistribute it and/or modify it
196 under the terms of the GNU Lesser General Public License as published
197 by the Free Software Foundation; either version 2 of the License, or
198 (at your option) any later version.
199 This library is distributed in the hope that it will be useful, but
201 WITHOUT ANY WARRANTY; without even the implied warranty of
202 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
203 Lesser General Public License for more details.
204 You should have received a copy of the GNU Lesser General Public
206 License along with this library; if not, write to the Free Software
207 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
208 02110-1301 USA
209libnbd-1.10.1 2021-10-25 nbd_aio_connect_unix(3)