Provided by: libnbd-dev_1.14.1-1_amd64 
NAME
nbd_set_opt_mode - control option mode, for pausing during option negotiation
SYNOPSIS
#include <libnbd.h>
int nbd_set_opt_mode (struct nbd_handle *h, bool enable);
DESCRIPTION
Set this flag to true in order to request that a connection command "nbd_connect_*" will
pause for negotiation options rather than proceeding all the way to the ready state, when
communicating with a newstyle server. This setting has no effect when connecting to an
oldstyle server.
When option mode is enabled, you have fine-grained control over which options are
negotiated, compared to the default of the server negotiating everything on your behalf
using settings made before starting the connection. To leave the mode and proceed on to
the ready state, you must use nbd_opt_go(3) successfully; a failed nbd_opt_go(3) returns
to the negotiating state to allow a change of export name before trying again. You may
also use nbd_opt_abort(3) to end the connection without finishing negotiation.
RETURN VALUE
If the call is successful the function returns 0.
ERRORS
On error "-1" is returned.
Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.
HANDLE STATE
The handle must be newly created, otherwise this call will return an error.
VERSION
This function first appeared in libnbd 1.4.
If you need to test if this function is available at compile time check if the following
macro is defined:
#define LIBNBD_HAVE_NBD_SET_OPT_MODE 1
EXAMPLE
This example is also available as examples/list-exports.c in the libnbd source code.
/* This example shows how to list NBD exports.
*
* To test this with qemu-nbd:
* $ qemu-nbd -x "hello" -t -k /tmp/sock disk.img
* $ ./run examples/list-exports /tmp/sock
* [0] hello
* Which export to connect to (-1 to quit)? 0
* Connecting to hello ...
* /tmp/sock: hello: size = 2048 bytes
*
* To test this with nbdkit (requires 1.22):
* $ nbdkit -U /tmp/sock sh - <<\EOF
* case $1 in
* list_exports) echo NAMES; echo foo; echo foobar ;;
* open) echo "$3" ;;
* get_size) echo "$2" | wc -c ;;
* pread) echo "$2" | dd bs=1 skip=$4 count=$3 ;;
* *) exit 2 ;;
* esac
* EOF
* $ ./run examples/list-exports /tmp/sock
* [0] foo
* [1] foobar
* Which export to connect to (-1 to quit)? 1
* Connecting to foobar ...
* /tmp/sock: foobar: size = 7 bytes
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <inttypes.h>
#include <errno.h>
#include <libnbd.h>
struct export_list {
int i;
char **names;
};
/* Callback function for nbd_opt_list */
static int
list_one (void *opaque, const char *name,
const char *description)
{
struct export_list *l = opaque;
char **names;
printf ("[%d] %s\n", l->i, name);
if (*description)
printf(" (%s)\n", description);
names = realloc (l->names,
(l->i + 1) * sizeof *names);
if (!names) {
perror ("realloc");
exit (EXIT_FAILURE);
}
names[l->i] = strdup (name);
if (!names[l->i]) {
perror ("strdup");
exit (EXIT_FAILURE);
}
l->names = names;
l->i++;
return 0;
}
int
main (int argc, char *argv[])
{
struct nbd_handle *nbd;
int i;
const char *name;
int64_t size;
struct export_list list = { 0 };
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);
}
/* Set opt mode. */
nbd_set_opt_mode (nbd, true);
/* Connect to the NBD server over a
* Unix domain socket. If we did not
* end up in option mode, then a
* listing is not possible.
*/
if (nbd_connect_unix (nbd, argv[1]) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
if (!nbd_aio_is_negotiating (nbd)) {
fprintf (stderr, "Server does not support "
"listing exports.\n");
exit (EXIT_FAILURE);
}
/* Print the export list. */
if (nbd_opt_list (nbd,
(nbd_list_callback) {
.callback = list_one,
.user_data = &list, }) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Display the list of exports. */
printf ("Which export to connect to? ");
if (scanf ("%d", &i) != 1) exit (EXIT_FAILURE);
if (i == -1) {
if (nbd_opt_abort (nbd) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
nbd_close (nbd);
exit (EXIT_SUCCESS);
}
if (i < 0 || i >= list.i) {
fprintf (stderr, "index %d out of range", i);
exit (EXIT_FAILURE);
}
name = list.names[i];
printf ("Connecting to %s ...\n", name);
/* Resume connecting to the chosen export. */
if (nbd_set_export_name (nbd, name) == -1 ||
nbd_opt_go (nbd) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
if (!nbd_aio_is_ready (nbd)) {
fprintf (stderr, "server closed early\n");
exit (EXIT_FAILURE);
}
/* Read the size in bytes and print it. */
size = nbd_get_size (nbd);
if (size == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
printf ("%s: %s: size = %" PRIi64 " bytes\n",
argv[1], name, size);
/* Close the libnbd handle. */
nbd_close (nbd);
for (i = 0; i < list.i; i++)
free (list.names[i]);
free (list.names);
exit (EXIT_SUCCESS);
}
SEE ALSO
nbd_aio_is_negotiating(3), nbd_create(3), nbd_get_opt_mode(3), nbd_opt_abort(3),
nbd_opt_go(3), nbd_opt_info(3), nbd_opt_list(3), nbd_opt_list_meta_context(3), libnbd(3).
AUTHORS
Eric Blake
Richard W.M. Jones
COPYRIGHT
Copyright (C) 2019-2021 Red Hat Inc.
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