examples/list-exports.c

   1 /* This example shows how to list NBD exports.
   2  *
   3  * To test this with qemu-nbd:
   4  *   $ qemu-nbd -x "hello" -t -k /tmp/sock disk.img
   5  *   $ ./run examples/list-exports /tmp/sock
   6  *   [0] hello
   7  *   Which export to connect to (-1 to quit)? 0
   8  *   Connecting to hello ...
   9  *   /tmp/sock: hello: size = 2048 bytes
  10  *
  11  * To test this with nbdkit (requires 1.22):
  12  *   $ nbdkit -U /tmp/sock sh - <<\EOF
  13  *   case $1 in
  14  *     list_exports) echo NAMES; echo foo; echo foobar ;;
  15  *     open) echo "$3" ;;
  16  *     get_size) echo "$2" | wc -c ;;
  17  *     pread) echo "$2" | dd bs=1 skip=$4 count=$3 ;;
  18  *     *) exit 2 ;;
  19  *   esac
  20  *   EOF
  21  *   $ ./run examples/list-exports /tmp/sock
  22  *   [0] foo
  23  *   [1] foobar
  24  *   Which export to connect to (-1 to quit)? 1
  25  *   Connecting to foobar ...
  26  *   /tmp/sock: foobar: size = 7 bytes
  27  */
  28
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <stdint.h>
  32 #include <string.h>
  33 #include <inttypes.h>
  34 #include <errno.h>
  35
  36 #include <libnbd.h>
  37
  38 struct export_list {
  39   int i;
  40   char **names;
  41 };
  42
  43 /* Callback function for nbd_opt_list */
  44 static int
  45 list_one (void *opaque, const char *name,
  46           const char *description)
  47 {
  48   struct export_list *l = opaque;
  49   char **names;
  50
  51   printf ("[%d] %s\n", l->i, name);
  52   if (*description)
  53     printf ("  (%s)\n", description);
  54   names = realloc (l->names,
  55                    (l->i + 1) * sizeof *names);
  56   if (!names) {
  57     perror ("realloc");
  58     exit (EXIT_FAILURE);
  59   }
  60   names[l->i] = strdup (name);
  61   if (!names[l->i]) {
  62     perror ("strdup");
  63     exit (EXIT_FAILURE);
  64   }
  65   l->names = names;
  66   l->i++;
  67   return 0;
  68 }
  69
  70 int
  71 main (int argc, char *argv[])
  72 {
  73   struct nbd_handle *nbd;
  74   int i;
  75   const char *name;
  76   int64_t size;
  77   struct export_list list = { 0 };
  78
  79   if (argc != 2) {
  80     fprintf (stderr, "%s socket\n", argv[0]);
  81     exit (EXIT_FAILURE);
  82   }
  83
  84   /* Create the libnbd handle. */
  85   nbd = nbd_create ();
  86   if (nbd == NULL) {
  87     fprintf (stderr, "%s\n", nbd_get_error ());
  88     exit (EXIT_FAILURE);
  89   }
  90
  91   /* Set opt mode. */
  92   nbd_set_opt_mode (nbd, true);
  93
  94   /* Connect to the NBD server over a
  95    * Unix domain socket.  If we did not
  96    * end up in option mode, then a
  97    * listing is not possible.
  98    */
  99   if (nbd_connect_unix (nbd, argv[1]) == -1) {
 100     fprintf (stderr, "%s\n", nbd_get_error ());
 101     exit (EXIT_FAILURE);
 102   }
 103   if (!nbd_aio_is_negotiating (nbd)) {
 104     fprintf (stderr, "Server does not support "
 105              "listing exports.\n");
 106     exit (EXIT_FAILURE);
 107   }
 108
 109   /* Print the export list. */
 110   if (nbd_opt_list (nbd,
 111                     (nbd_list_callback) {
 112                       .callback = list_one,
 113                       .user_data = &list, }) == -1) {
 114     fprintf (stderr, "%s\n", nbd_get_error ());
 115     exit (EXIT_FAILURE);
 116   }
 117
 118   /* Display the list of exports. */
 119   printf ("Which export to connect to? ");
 120   if (scanf ("%d", &i) != 1) exit (EXIT_FAILURE);
 121   if (i == -1) {
 122     if (nbd_opt_abort (nbd) == -1) {
 123       fprintf (stderr, "%s\n", nbd_get_error ());
 124       exit (EXIT_FAILURE);
 125     }
 126     nbd_close (nbd);
 127     exit (EXIT_SUCCESS);
 128   }
 129   if (i < 0 || i >= list.i) {
 130     fprintf (stderr, "index %d out of range", i);
 131     exit (EXIT_FAILURE);
 132   }
 133   name = list.names[i];
 134   printf ("Connecting to %s ...\n", name);
 135
 136   /* Resume connecting to the chosen export. */
 137   if (nbd_set_export_name (nbd, name) == -1 ||
 138       nbd_opt_go (nbd) == -1) {
 139     fprintf (stderr, "%s\n", nbd_get_error ());
 140     exit (EXIT_FAILURE);
 141   }
 142   if (!nbd_aio_is_ready (nbd)) {
 143     fprintf (stderr, "server closed early\n");
 144     exit (EXIT_FAILURE);
 145   }
 146
 147   /* Read the size in bytes and print it. */
 148   size = nbd_get_size (nbd);
 149   if (size == -1) {
 150     fprintf (stderr, "%s\n", nbd_get_error ());
 151     exit (EXIT_FAILURE);
 152   }
 153   printf ("%s: %s: size = %" PRIi64 " bytes\n",
 154           argv[1], name, size);
 155
 156   /* Close the libnbd handle. */
 157   nbd_close (nbd);
 158
 159   for (i = 0; i < list.i; i++)
 160     free (list.names[i]);
 161   free (list.names);
 162
 163   exit (EXIT_SUCCESS);
 164 }