1nbd_aio_in_flight(3) LIBNBD nbd_aio_in_flight(3)
2
6 nbd_aio_in_flight - check how many aio commands are still in flight
7
9 #include <libnbd.h>
10 int nbd_aio_in_flight (struct nbd_handle *h);
12
14 Return the number of in-flight aio commands that are still awaiting a
15 response from the server before they can be retired. If this returns a
16 non-zero value when requesting a disconnect from the server (see
17 nbd_aio_disconnect(3) and nbd_shutdown(3)), libnbd does not try to wait
18 for those commands to complete gracefully; if the server strands
19 commands while shutting down, nbd_aio_command_completed(3) will report
20 those commands as failed with a status of "ENOTCONN".
21
23 This call returns an integer ≥ 0.
24
26 On error "-1" is returned.
27 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
29 of the error.
30
32 The handle must be connected with the server, or shut down, or dead,
33 otherwise this call will return an error.
34
36 This function first appeared in libnbd 1.0.
37 If you need to test if this function is available at compile time check
39 if the following macro is defined:
40 #define LIBNBD_HAVE_NBD_AIO_IN_FLIGHT 1
42
44 This example is also available as examples/aio-connect-read.c in the
45 libnbd source code.
46 /* This example shows how to use the AIO (asynchronous) low
48 * level API to connect to a server and read the disk.
49 *
50 * Here are a few ways to try this example:
51 *
52 * nbdkit -U - linuxdisk . \
53 * --run './aio-connect-read $unixsocket'
54 *
55 * nbdkit -U - floppy . \
56 * --run './aio-connect-read $unixsocket'
57 *
58 * nbdkit -U - pattern size=1M \
59 * --run './aio-connect-read $unixsocket'
60 */
61 #include <stdio.h>
63 #include <stdlib.h>
64 #include <stdint.h>
65 #include <inttypes.h>
66 #include <assert.h>
67 #include <libnbd.h>
69 #define NR_SECTORS 32
71 #define SECTOR_SIZE 512
72 struct data {
74 uint64_t offset;
75 char sector[SECTOR_SIZE];
76 };
77 static int
79 hexdump (void *user_data, int *error)
80 {
81 struct data *data = user_data;
82 FILE *pp;
83 printf ("sector at offset 0x%" PRIx64 ":\n",
85 data->offset);
86 pp = popen ("hexdump -C", "w");
87 if (pp == NULL) {
88 perror ("popen: hexdump");
89 exit (EXIT_FAILURE);
90 }
91 fwrite (data->sector, SECTOR_SIZE, 1, pp);
92 pclose (pp);
93 printf ("\n");
94 /* Returning 1 from the callback automatically retires
96 * the command.
97 */
98 return 1;
99 }
100 static struct data data[NR_SECTORS];
102 int
104 main (int argc, char *argv[])
105 {
106 struct nbd_handle *nbd;
107 size_t i;
108 if (argc != 2) {
110 fprintf (stderr, "%s socket\n", argv[0]);
111 exit (EXIT_FAILURE);
112 }
113 /* Create the libnbd handle. */
115 nbd = nbd_create ();
116 if (nbd == NULL) {
117 fprintf (stderr, "%s\n", nbd_get_error ());
118 exit (EXIT_FAILURE);
119 }
120 /* Connect to the NBD server over a Unix domain socket.
122 * This only starts the connection.
123 */
124 if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
125 fprintf (stderr, "%s\n", nbd_get_error ());
126 exit (EXIT_FAILURE);
127 }
128 /* Wait for the connection to complete. The use of
130 * nbd_poll here is only as an example. You could also
131 * integrate this with poll(2), glib or another main
132 * loop. Read libnbd(3) and the source file lib/poll.c.
133 */
134 while (!nbd_aio_is_ready (nbd)) {
135 if (nbd_poll (nbd, -1) == -1) {
136 fprintf (stderr, "%s\n", nbd_get_error ());
137 exit (EXIT_FAILURE);
138 }
139 }
140 assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
142 /* Issue read commands for the first NR sectors. */
144 for (i = 0; i < NR_SECTORS; ++i) {
145 data[i].offset = i * SECTOR_SIZE;
146 /* The callback (hexdump) is called when the command
148 * completes. The buffer must continue to exist while
149 * the command is running.
150 */
151 if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
152 data[i].offset,
153 (nbd_completion_callback) {
154 .callback = hexdump,
155 .user_data = &data[i],
156 }, 0) == -1) {
157 fprintf (stderr, "%s\n", nbd_get_error ());
158 exit (EXIT_FAILURE);
159 }
160 }
161 /* Run the main loop until all the commands have
163 * completed and retired. Again the use of nbd_poll
164 * here is only as an example.
165 */
166 while (nbd_aio_in_flight (nbd) > 0) {
167 if (nbd_poll (nbd, -1) == -1) {
168 fprintf (stderr, "%s\n", nbd_get_error ());
169 exit (EXIT_FAILURE);
170 }
171 }
172 /* Close the libnbd handle. */
174 nbd_close (nbd);
175 exit (EXIT_SUCCESS);
177 }
178
180 nbd_aio_command_completed(3), nbd_aio_disconnect(3), nbd_create(3),
181 nbd_shutdown(3), libnbd(3).
182
184 Eric Blake
185 Richard W.M. Jones
187
189 Copyright (C) 2019-2021 Red Hat Inc.
190
192 This library is free software; you can redistribute it and/or modify it
193 under the terms of the GNU Lesser General Public License as published
194 by the Free Software Foundation; either version 2 of the License, or
195 (at your option) any later version.
196 This library is distributed in the hope that it will be useful, but
198 WITHOUT ANY WARRANTY; without even the implied warranty of
199 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
200 Lesser General Public License for more details.
201 You should have received a copy of the GNU Lesser General Public
203 License along with this library; if not, write to the Free Software
204 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
205 02110-1301 USA
206libnbd-1.10.1 2021-10-25 nbd_aio_in_flight(3)