1nbd_aio_in_flight(3)                LIBNBD                nbd_aio_in_flight(3)
2
3
4

NAME

6       nbd_aio_in_flight - check how many aio commands are still in flight
7

SYNOPSIS

9        #include <libnbd.h>
10
11        int nbd_aio_in_flight (struct nbd_handle *h);
12

DESCRIPTION

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

RETURN VALUE

23       This call returns an integer ≥ 0.
24

ERRORS

26       On error "-1" is returned.
27
28       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
29       of the error.
30

HANDLE STATE

32       The handle must be connected with the server, or shut down, or dead,
33       otherwise this call will return an error.
34

VERSION

36       This function first appeared in libnbd 1.0.
37
38       If you need to test if this function is available at compile time check
39       if the following macro is defined:
40
41        #define LIBNBD_HAVE_NBD_AIO_IN_FLIGHT 1
42

EXAMPLE

44       This example is also available as examples/aio-connect-read.c in the
45       libnbd source code.
46
47        /* 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
62        #include <stdio.h>
63        #include <stdlib.h>
64        #include <stdint.h>
65        #include <inttypes.h>
66        #include <assert.h>
67
68        #include <libnbd.h>
69
70        #define NR_SECTORS 32
71        #define SECTOR_SIZE 512
72
73        struct data {
74          uint64_t offset;
75          char sector[SECTOR_SIZE];
76        };
77
78        static int
79        hexdump (void *user_data, int *error)
80        {
81          struct data *data = user_data;
82          FILE *pp;
83
84          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
95          /* Returning 1 from the callback automatically retires
96           * the command.
97           */
98          return 1;
99        }
100
101        int
102        main (int argc, char *argv[])
103        {
104          struct nbd_handle *nbd;
105          struct data data[NR_SECTORS];
106          size_t i;
107
108          if (argc != 2) {
109            fprintf (stderr, "%s socket\n", argv[0]);
110            exit (EXIT_FAILURE);
111          }
112
113          /* Create the libnbd handle. */
114          nbd = nbd_create ();
115          if (nbd == NULL) {
116            fprintf (stderr, "%s\n", nbd_get_error ());
117            exit (EXIT_FAILURE);
118          }
119
120          /* Connect to the NBD server over a Unix domain socket.
121           * This only starts the connection.
122           */
123          if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
124            fprintf (stderr, "%s\n", nbd_get_error ());
125            exit (EXIT_FAILURE);
126          }
127
128          /* Wait for the connection to complete.  The use of
129           * nbd_poll here is only as an example.  You could also
130           * integrate this with poll(2), glib or another main
131           * loop.  Read libnbd(3) and the source file lib/poll.c.
132           */
133          while (!nbd_aio_is_ready (nbd)) {
134            if (nbd_poll (nbd, -1) == -1) {
135              fprintf (stderr, "%s\n", nbd_get_error ());
136              exit (EXIT_FAILURE);
137            }
138          }
139
140          assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
141
142          /* Issue read commands for the first NR sectors. */
143          for (i = 0; i < NR_SECTORS; ++i) {
144            data[i].offset = i * SECTOR_SIZE;
145
146            /* The callback (hexdump) is called when the command
147             * completes.  The buffer must continue to exist while
148             * the command is running.
149             */
150            if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
151                               data[i].offset,
152                               (nbd_completion_callback) {
153                                 .callback = hexdump,
154                                 .user_data = &data[i],
155                               }, 0) == -1) {
156              fprintf (stderr, "%s\n", nbd_get_error ());
157              exit (EXIT_FAILURE);
158            }
159          }
160
161          /* Run the main loop until all the commands have
162           * completed and retired.  Again the use of nbd_poll
163           * here is only as an example.
164           */
165          while (nbd_aio_in_flight (nbd) > 0) {
166            if (nbd_poll (nbd, -1) == -1) {
167              fprintf (stderr, "%s\n", nbd_get_error ());
168              exit (EXIT_FAILURE);
169            }
170          }
171
172          /* Close the libnbd handle. */
173          nbd_close (nbd);
174
175          exit (EXIT_SUCCESS);
176        }
177

SEE ALSO

179       nbd_aio_command_completed(3), nbd_aio_disconnect(3), nbd_create(3),
180       nbd_shutdown(3), libnbd(3).
181

AUTHORS

183       Eric Blake
184
185       Richard W.M. Jones
186
188       Copyright (C) 2019-2021 Red Hat Inc.
189

LICENSE

191       This library is free software; you can redistribute it and/or modify it
192       under the terms of the GNU Lesser General Public License as published
193       by the Free Software Foundation; either version 2 of the License, or
194       (at your option) any later version.
195
196       This library is distributed in the hope that it will be useful, but
197       WITHOUT ANY WARRANTY; without even the implied warranty of
198       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
199       Lesser General Public License for more details.
200
201       You should have received a copy of the GNU Lesser General Public
202       License along with this library; if not, write to the Free Software
203       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
204       02110-1301 USA
205
206
207
208libnbd-1.7.12                     2021-05-29              nbd_aio_in_flight(3)
Impressum