nbd_aio_connect_unix - connect to the NBD server over a Unix domain socket
#include <libnbd.h>
int nbd_aio_connect_unix (
struct nbd_handle *h, const char *unixsocket
);Begin connecting to the NBD server over Unix domain socket (unixsocket). Parameters behave as documented in nbd_connect_unix(3).
You can check if the connection attempt is still underway by calling nbd_aio_is_connecting(3). If nbd_set_opt_mode(3) is enabled, the connection is ready for manual option negotiation once nbd_aio_is_negotiating(3) returns true; otherwise, the connection attempt will include the NBD handshake, and is ready for use once nbd_aio_is_ready(3) returns true.
If the call is successful the function returns 0.
On error -1 is returned.
Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.
The following parameters must not be NULL: h, unixsocket. For more information see "Non-NULL parameters" in libnbd(3).
nbd_aio_connect_unix can be called when the handle is in the following state:
┌─────────────────────────────────────┬─────────────────────────┐
│ Handle created, before connecting │ ✅ allowed │
│ Connecting │ ❌ error │
│ Connecting & handshaking (opt_mode) │ ❌ error │
│ Connected to the server │ ❌ error │
│ Connection shut down │ ❌ error │
│ Handle dead │ ❌ error │
└─────────────────────────────────────┴─────────────────────────┘This function first appeared in libnbd 1.0.
If you need to test if this function is available at compile time check if the following macro is defined:
#define LIBNBD_HAVE_NBD_AIO_CONNECT_UNIX 1This example is also available as examples/aio-connect-read.c in the libnbd source code.
/* This example shows how to use the AIO (asynchronous) low
* level API to connect to a server and read the disk.
*
* Here are a few ways to try this example:
*
* nbdkit -U - linuxdisk . \
* --run './aio-connect-read $unixsocket'
*
* nbdkit -U - floppy . \
* --run './aio-connect-read $unixsocket'
*
* nbdkit -U - pattern size=1M \
* --run './aio-connect-read $unixsocket'
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>
#include <errno.h>
#include <assert.h>
#include <libnbd.h>
#define NR_SECTORS 32
#define SECTOR_SIZE 512
struct data {
uint64_t offset;
char sector[SECTOR_SIZE];
};
static int
hexdump (void *user_data, int *error)
{
struct data *data = user_data;
FILE *pp;
if (*error) {
errno = *error;
perror ("failed to read");
exit (EXIT_FAILURE);
}
printf ("sector at offset 0x%" PRIx64 ":\n",
data->offset);
pp = popen ("hexdump -C", "w");
if (pp == NULL) {
perror ("popen: hexdump");
exit (EXIT_FAILURE);
}
fwrite (data->sector, SECTOR_SIZE, 1, pp);
pclose (pp);
printf ("\n");
/* Returning 1 from the callback automatically retires
* the command.
*/
return 1;
}
static struct data data[NR_SECTORS];
int
main (int argc, char *argv[])
{
struct nbd_handle *nbd;
size_t i;
if (argc != 2) {
fprintf (stderr, "%s socket\n", argv[0]);
exit (EXIT_FAILURE);
}
/* Create the libnbd handle. */
nbd = nbd_create ();
if (nbd == NULL) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Connect to the NBD server over a Unix domain socket.
* This only starts the connection.
*/
if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Wait for the connection to complete. The use of
* nbd_poll here is only as an example. You could also
* integrate this with poll(2), glib or another main
* loop. Read libnbd(3) and the source file lib/poll.c.
*/
while (!nbd_aio_is_ready (nbd)) {
if (nbd_poll (nbd, -1) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
/* Issue read commands for the first NR sectors. */
for (i = 0; i < NR_SECTORS; ++i) {
data[i].offset = i * SECTOR_SIZE;
/* The callback (hexdump) is called when the command
* completes. The buffer must continue to exist while
* the command is running.
*/
if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
data[i].offset,
(nbd_completion_callback) {
.callback = hexdump,
.user_data = &data[i],
}, 0) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
/* Run the main loop until all the commands have
* completed and retired. Again the use of nbd_poll
* here is only as an example.
*/
while (nbd_aio_in_flight (nbd) > 0) {
if (nbd_poll (nbd, -1) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
/* Close the libnbd handle. */
nbd_close (nbd);
exit (EXIT_SUCCESS);
}nbd_aio_is_connecting(3), nbd_aio_is_negotiating(3), nbd_aio_is_ready(3), nbd_connect_unix(3), nbd_create(3), nbd_set_opt_mode(3), libnbd(3).
Eric Blake
Richard W.M. Jones
Copyright Red Hat
This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA