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NAME

nbd_aio_in_flight - check how many aio commands are still in flight

SYNOPSIS

#include <libnbd.h>
int nbd_aio_in_flight (
struct nbd_handle *h
);

Return the number of in-flight aio commands that are still awaiting a response from the server before they can be retired. If this returns a non-zero value when requesting a disconnect from the server (see nbd_aio_disconnect(3) and nbd_shutdown(3)), libnbd does not try to wait for those commands to complete gracefully; if the server strands commands while shutting down, nbd_aio_command_completed(3) will report those commands as failed with a status of "ENOTCONN".

RETURN VALUE

This call returns an integer ≥ 0.

ERRORS

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". For more information see "Non-NULL parameters" in libnbd(3).

HANDLE STATE

nbd_aio_in_flight can be called when the handle is in the following states:

┌─────────────────────────────────────┬─────────────────────────┐
│ Handle created, before connecting │ ❌ error │
│ Connecting │ ❌ error │
│ Connecting & handshaking (opt_mode) │ ❌ error │
│ Connected to the server │ ✅ allowed │
│ Connection shut down │ ✅ allowed │
│ Handle dead │ ✅ allowed │
└─────────────────────────────────────┴─────────────────────────┘

VERSION

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_IN_FLIGHT 1

EXAMPLE

This 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);
}

AUTHORS

Eric Blake

Richard W.M. Jones

COPYRIGHT

LICENSE

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

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