plugins/example3/example3.c

   1 /* nbdkit
   2  * Copyright (C) 2013 Red Hat Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 /* example3:
  34  *
  35  * A simple read-write filesystem which stores all changes in
  36  * a temporary file that is thrown away after each connection.
  37  */
  38
  39 #include <config.h>
  40
  41 #include <stdio.h>
  42 #include <stdlib.h>
  43 #include <stdint.h>
  44 #include <string.h>
  45 #include <fcntl.h>
  46 #include <unistd.h>
  47
  48 #include <nbdkit-plugin.h>
  49
  50 #ifndef HAVE_FDATASYNC
  51 #define fdatasync fsync
  52 #endif
  53
  54 /* The size of disk in bytes (initialized by size=<SIZE> parameter).
  55  * If size parameter is not specified, it defaults to 100M.
  56  */
  57 static uint64_t size = 100 * 1024 * 1024;
  58
  59 /* If you want to display extra information about the plugin when
  60  * the user does ‘nbdkit example3 --dump-plugin’ then you can print
  61  * ‘key=value’ lines here.
  62  */
  63 static void
  64 example3_dump_plugin (void)
  65 {
  66   printf ("example3_extra=hello\n");
  67 }
  68
  69 /* Called for each key=value passed on the command line.  This plugin
  70  * only accepts optional size=<SIZE> parameter.
  71  */
  72 static int
  73 example3_config (const char *key, const char *value)
  74 {
  75   int64_t r;
  76
  77   if (strcmp (key, "size") == 0) {
  78     r = nbdkit_parse_size (value);
  79     if (r == -1)
  80       return -1;
  81     size = (uint64_t) r;
  82   }
  83   else {
  84     nbdkit_error ("unknown parameter '%s'", key);
  85     return -1;
  86   }
  87
  88   return 0;
  89 }
  90
  91 #define example3_config_help \
  92   "size=<SIZE>  (optional) Size of the backing disk (default: 100M)"
  93
  94 /* The per-connection handle. */
  95 struct example3_handle {
  96   int fd;
  97 };
  98
  99 /* Create the per-connection handle.
 100  *
 101  * Note we ignore the 'readonly' parameter.  In effect this means that
 102  * we ignore the -r option on the nbdkit command line, which sort of
 103  * makes sense for this particular plugin.
 104  */
 105 static void *
 106 example3_open (int readonly)
 107 {
 108   struct example3_handle *h;
 109   char template[] = LARGE_TMPDIR "/diskXXXXXX";
 110
 111   h = malloc (sizeof *h);
 112   if (h == NULL) {
 113     nbdkit_error ("malloc: %m");
 114     return NULL;
 115   }
 116
 117   h->fd = mkstemp (template);
 118   if (h->fd == -1) {
 119     nbdkit_error ("mkstemp: %s: %m", template);
 120     free (h);
 121     return NULL;
 122   }
 123
 124   unlink (template);
 125
 126   /* This creates a raw-format sparse file of the required size. */
 127   if (ftruncate (h->fd, size) == -1) {
 128     nbdkit_error ("ftruncate: %m");
 129     close (h->fd);
 130     free (h);
 131     return NULL;
 132   }
 133
 134   return h;
 135 }
 136
 137 /* Free up the per-connection handle. */
 138 static void
 139 example3_close (void *handle)
 140 {
 141   struct example3_handle *h = handle;
 142
 143   close (h->fd);
 144   free (h);
 145 }
 146
 147 /* In fact NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS would work here.
 148  * However for the benefit of people who blindly cut and paste code
 149  * without bothering to read any documentation, leave this at a safe
 150  * default.
 151  */
 152 #define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS
 153
 154 /* Get the file size. */
 155 static int64_t
 156 example3_get_size (void *handle)
 157 {
 158   return (int64_t) size;
 159 }
 160
 161 /* Read data from the file. */
 162 static int
 163 example3_pread (void *handle, void *buf, uint32_t count, uint64_t offset)
 164 {
 165   struct example3_handle *h = handle;
 166
 167   while (count > 0) {
 168     ssize_t r = pread (h->fd, buf, count, offset);
 169     if (r == -1) {
 170       nbdkit_error ("pead: %m");
 171       return -1;
 172     }
 173     if (r == 0) {
 174       nbdkit_error ("pread: unexpected end of file");
 175       return -1;
 176     }
 177     buf += r;
 178     count -= r;
 179     offset += r;
 180   }
 181
 182   return 0;
 183 }
 184
 185 /* Write data to the file. */
 186 static int
 187 example3_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset)
 188 {
 189   struct example3_handle *h = handle;
 190
 191   while (count > 0) {
 192     ssize_t r = pwrite (h->fd, buf, count, offset);
 193     if (r == -1) {
 194       nbdkit_error ("pwrite: %m");
 195       return -1;
 196     }
 197     buf += r;
 198     count -= r;
 199     offset += r;
 200   }
 201
 202   return 0;
 203 }
 204
 205 /* Flush the file to disk. */
 206 static int
 207 example3_flush (void *handle)
 208 {
 209   struct example3_handle *h = handle;
 210
 211   if (fdatasync (h->fd) == -1) {
 212     nbdkit_error ("fdatasync: %m");
 213     return -1;
 214   }
 215
 216   return 0;
 217 }
 218
 219 static struct nbdkit_plugin plugin = {
 220   .name              = "example3",
 221   .version           = PACKAGE_VERSION,
 222   .dump_plugin       = example3_dump_plugin,
 223   .config            = example3_config,
 224   .config_help       = example3_config_help,
 225   .open              = example3_open,
 226   .close             = example3_close,
 227   .get_size          = example3_get_size,
 228   .pread             = example3_pread,
 229   .pwrite            = example3_pwrite,
 230   .flush             = example3_flush,
 231   /* In this plugin, errno is preserved properly along error return
 232    * paths from failed system calls.
 233    */
 234   .errno_is_preserved = 1,
 235 };
 236
 237 NBDKIT_REGISTER_PLUGIN(plugin)