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 it is usually better to use nbd_connect_command(3).

 ┌─────────┬─────────┐    ┌───────────────┐
 │ program │ libnbd  │    │  qemu-nbd or  │
 │         │         │    │  other server │
 │         │ socket ╍╍╍╍╍╍╍╍▶             │
 └─────────┴─────────┘    └───────────────┘

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 1.2.

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, 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_connect_command(3), nbd_create(3), nbd_kill_subprocess(3), libnbd(3), qemu-nbd(1), http://0pointer.de/blog/projects/socket-activation.html.

AUTHORS¶

Eric Blake

Richard W.M. Jones

COPYRIGHT¶

Copyright (C) 2019-2020 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