nbd_connect_systemd_socket_activation(3)

1nbd_connect_systemd_socket_activationL(I3Bn)NbBdD_connect_systemd_socket_activation(3)
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NAME

6       nbd_connect_systemd_socket_activation - connect using systemd socket
7       activation
8

SYNOPSIS

10        #include <libnbd.h>
11
12        int nbd_connect_systemd_socket_activation (struct nbd_handle *h,
13                                                   char **argv);
14

DESCRIPTION

16       Run the command as a subprocess and connect to it using systemd socket
17       activation.
18
19       This is especially useful for running qemu-nbd(1) as a subprocess of
20       libnbd, for example to use it to open qcow2 files.  To run nbdkit as a
21       subprocess it is usually better to use nbd_connect_command(3).
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23   Socket activation
24       Libnbd will fork the "argv" command and pass an NBD socket to it using
25       special "LISTEN_*" environment variables (as defined by the systemd
26       socket activation protocol).
27
28        ┌─────────┬─────────┐    ┌───────────────┐
29        │ program │ libnbd  │    │  qemu-nbd or  │
30        │         │         │    │  other server │
31        │         │ socket ╍╍╍╍╍╍╍╍▶             │
32        └─────────┴─────────┘    └───────────────┘
33
34       When the NBD handle is closed the server subprocess is killed.
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RETURN VALUE

37       If the call is successful the function returns 0.
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ERRORS

40       On error "-1" is returned.
41
42       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
43       of the error.
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HANDLE STATE

46       The handle must be newly created, otherwise this call will return an
47       error.
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VERSION

50       This function first appeared in libnbd 1.2.
51
52       If you need to test if this function is available at compile time check
53       if the following macro is defined:
54
55        #define LIBNBD_HAVE_NBD_CONNECT_SYSTEMD_SOCKET_ACTIVATION 1
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EXAMPLE

58       This example is also available as examples/open-qcow2.c in the libnbd
59       source code.
60
61        /* This example shows how to use qemu-nbd
62         * to open a local qcow2 file.
63         */
64
65        #include <stdio.h>
66        #include <stdlib.h>
67        #include <string.h>
68
69        #include <libnbd.h>
70
71        int
72        main (int argc, char *argv[])
73        {
74          const char *filename;
75          struct nbd_handle *nbd;
76          char buf[512];
77          FILE *fp;
78
79          if (argc != 2) {
80            fprintf (stderr, "open-qcow2 file.qcow2\n");
81            exit (EXIT_FAILURE);
82          }
83          filename = argv[1];
84
85          /* Create the libnbd handle. */
86          nbd = nbd_create ();
87          if (nbd == NULL) {
88            fprintf (stderr, "%s\n", nbd_get_error ());
89            exit (EXIT_FAILURE);
90          }
91
92          /* Run qemu-nbd as a subprocess using
93           * systemd socket activation.
94           */
95          char *args[] = {
96            "qemu-nbd", "-f", "qcow2",
97            (char *) filename,
98            NULL
99          };
100          if (nbd_connect_systemd_socket_activation (nbd,
101                                                     args) == -1) {
102            fprintf (stderr, "%s\n", nbd_get_error ());
103            exit (EXIT_FAILURE);
104          }
105
106          /* Read the first sector and print it. */
107          if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
108            fprintf (stderr, "%s\n", nbd_get_error ());
109            exit (EXIT_FAILURE);
110          }
111
112          fp = popen ("hexdump -C", "w");
113          if (fp == NULL) {
114            perror ("popen: hexdump");
115            exit (EXIT_FAILURE);
116          }
117          fwrite (buf, sizeof buf, 1, fp);
118          pclose (fp);
119
120          /* Close the libnbd handle. */
121          nbd_close (nbd);
122
123          exit (EXIT_SUCCESS);
124        }
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AUTHORS

132       Eric Blake
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134       Richard W.M. Jones
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COPYRIGHT

137       Copyright (C) 2019-2020 Red Hat Inc.
138

LICENSE

140       This library is free software; you can redistribute it and/or modify it
141       under the terms of the GNU Lesser General Public License as published
142       by the Free Software Foundation; either version 2 of the License, or
143       (at your option) any later version.
144
145       This library is distributed in the hope that it will be useful, but
146       WITHOUT ANY WARRANTY; without even the implied warranty of
147       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
148       Lesser General Public License for more details.
149
150       You should have received a copy of the GNU Lesser General Public
151       License along with this library; if not, write to the Free Software
152       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
153       02110-1301 USA
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157libnbd-1.6.2                      2021-n0b3d-_0c2onnect_systemd_socket_activation(3)