nbd_connect_systemd_socket_activation - connect using systemd socket activation

NAME  SYNOPSIS  DESCRIPTION  Socket activation  RETURN VALUE  ERRORS  HANDLE STATE  VERSION  EXAMPLE  SEE ALSO  AUTHORS  COPYRIGHT  LICENSE 

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NAME

nbd_connect_systemd_socket_activation − connect using systemd socket activation

SYNOPSIS

#include <libnbd.h>
int nbd_connect_systemd_socket_activation (
struct nbd_handle *h, char **argv
);

DESCRIPTION

Run the command as a subprocess and connect to it using systemd socket activation.

This is especially useful for running qemu−nbd(1) as a subprocess of libnbd, for example to use it to open qcow2 files.

To run nbdkit as a subprocess, this function can be used, or nbd_connect_command(3).

To run nbd−server(1) as a subprocess, this function cannot be used, you must use nbd_connect_command(3).

Socket activation

Libnbd will fork the "argv" command and pass an NBD socket to it using special "LISTEN_*" environment variables (as defined by the systemd socket activation protocol).

âââââââââââ¬ââââââââââ âââââââââââââââââ
â program â libnbd â â qemu−nbd or â
â â â â other server â
â â socket ââââââââⶠâ
âââââââââââ´ââââââââââ âââââââââââââââââ

When the NBD handle is closed the server subprocess is killed.

Socket name

The socket activation protocol lets you optionally give the socket a name. If used, the name is passed to the NBD server using the "LISTEN_FDNAMES" environment variable. To provide a socket name, call nbd_set_socket_activation_name(3) before calling the connect function.

This call returns when the connection has been made. By default, this proceeds all the way to transmission phase, but nbd_set_opt_mode(3) can be used for manual control over option negotiation performed before transmission phase.

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.

The following parameters must not be NULL: "h", "argv". For more information see "Non−NULL parameters" in libnbd(3).

HANDLE STATE

nbd_connect_systemd_socket_activation can be called when the handle is in the following state:

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â Handle created, before connecting â â allowed â
â Connecting â â error â
â Connecting & handshaking (opt_mode) â â error â
â Connected to the server â â error â
â Connection shut down â â error â
â Handle dead â â error â
âââââââââââââââââââââââââââââââââââââââ´ââââââââââââââââââââââââââ

VERSION

This function first appeared in libnbd 1.2.

If you need to test if this function is available at compile time check if the following macro is defined:

#define LIBNBD_HAVE_NBD_CONNECT_SYSTEMD_SOCKET_ACTIVATION 1

EXAMPLE

This example is also available as examples/open−qcow2.c in the libnbd source code.

/* This example shows how to use qemu−nbd
* to open a local qcow2 file.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libnbd.h>
int
main (int argc, const char *argv[])
{
const char *filename;
struct nbd_handle *nbd;
char buf[512];
FILE *fp;
if (argc != 2) {
fprintf (stderr, "open−qcow2 file.qcow2\n");
exit (EXIT_FAILURE);
}
filename = argv[1];
/* Create the libnbd handle. */
nbd = nbd_create ();
if (nbd == NULL) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Run qemu−nbd as a subprocess using
* systemd socket activation.
*/
char *args[] = {
"qemu−nbd", "−f", "qcow2",
(char *)filename,
NULL
};
if (nbd_connect_systemd_socket_activation (nbd,
args) == −1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Read the first sector and print it. */
if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == −1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
fp = popen ("hexdump −C", "w");
if (fp == NULL) {
perror ("popen: hexdump");
exit (EXIT_FAILURE);
}
fwrite (buf, sizeof buf, 1, fp);
pclose (fp);
/* Close the libnbd handle. */
nbd_close (nbd);
exit (EXIT_SUCCESS);
}

SEE ALSO

nbd_aio_connect_systemd_socket_activation(3), nbd_connect_command(3), nbd_create(3), nbd_get_socket_activation_name(3), nbd_get_subprocess_pid(3), nbd_kill_subprocess(3), nbd_set_opt_mode(3), nbd_set_socket_activation_name(3), libnbd(3), qemu−nbd(1), http://0pointer.de/blog/projects/socket−activation.html.

AUTHORS

Eric Blake

Richard W.M. Jones

COPYRIGHT

Copyright Red Hat

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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