plugins/example3/example3.c

   1 /* nbdkit
   2  * Copyright Red Hat
   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 #define NBDKIT_API_VERSION 2
  49 #include <nbdkit-plugin.h>
  50
  51 #ifndef HAVE_FDATASYNC
  52 #define fdatasync fsync
  53 #endif
  54
  55 /* The size of disk in bytes (initialized by size=<SIZE> parameter).
  56  * If size parameter is not specified, it defaults to 100M.
  57  */
  58 static uint64_t size = 100 * 1024 * 1024;
  59
  60 /* If you want to display extra information about the plugin when
  61  * the user does ‘nbdkit example3 --dump-plugin’ then you can print
  62  * ‘key=value’ lines here.
  63  */
  64 static void
  65 example3_dump_plugin (void)
  66 {
  67   printf ("example3_extra=hello\n");
  68 }
  69
  70 /* Called for each key=value passed on the command line.  This plugin
  71  * only accepts optional size=<SIZE> parameter.
  72  */
  73 static int
  74 example3_config (const char *key, const char *value)
  75 {
  76   int64_t r;
  77
  78   if (strcmp (key, "size") == 0) {
  79     r = nbdkit_parse_size (value);
  80     if (r == -1)
  81       return -1;
  82     size = (uint64_t) r;
  83   }
  84   else {
  85     nbdkit_error ("unknown parameter '%s'", key);
  86     return -1;
  87   }
  88
  89   return 0;
  90 }
  91
  92 #define example3_config_help \
  93   "size=<SIZE>  (optional) Size of the backing disk (default: 100M)"
  94
  95 /* The per-connection handle. */
  96 struct example3_handle {
  97   int fd;
  98 };
  99
 100 /* Create the per-connection handle.
 101  *
 102  * Note we ignore the 'readonly' parameter.  In effect this means that
 103  * we ignore the -r option on the nbdkit command line, which sort of
 104  * makes sense for this particular plugin.
 105  */
 106 static void *
 107 example3_open (int readonly)
 108 {
 109   struct example3_handle *h;
 110   char template[] = LARGE_TMPDIR "/diskXXXXXX";
 111
 112   h = malloc (sizeof *h);
 113   if (h == NULL) {
 114     nbdkit_error ("malloc: %m");
 115     return NULL;
 116   }
 117
 118   h->fd = mkstemp (template);
 119   if (h->fd == -1) {
 120     nbdkit_error ("mkstemp: %s: %m", template);
 121     free (h);
 122     return NULL;
 123   }
 124
 125   unlink (template);
 126
 127   /* This creates a raw-format sparse file of the required size. */
 128   if (ftruncate (h->fd, size) == -1) {
 129     nbdkit_error ("ftruncate: %m");
 130     close (h->fd);
 131     free (h);
 132     return NULL;
 133   }
 134
 135   return h;
 136 }
 137
 138 /* Free up the per-connection handle. */
 139 static void
 140 example3_close (void *handle)
 141 {
 142   struct example3_handle *h = handle;
 143
 144   close (h->fd);
 145   free (h);
 146 }
 147
 148 /* In fact NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS would work here.
 149  * However for the benefit of people who blindly cut and paste code
 150  * without bothering to read any documentation, leave this at a safe
 151  * default.
 152  */
 153 #define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS
 154
 155 /* Get the file size. */
 156 static int64_t
 157 example3_get_size (void *handle)
 158 {
 159   return (int64_t) size;
 160 }
 161
 162 /* Read data from the file. */
 163 static int
 164 example3_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
 165                 uint32_t flags)
 166 {
 167   struct example3_handle *h = handle;
 168
 169   while (count > 0) {
 170     ssize_t r = pread (h->fd, buf, count, offset);
 171     if (r == -1) {
 172       nbdkit_error ("pead: %m");
 173       return -1;
 174     }
 175     if (r == 0) {
 176       nbdkit_error ("pread: unexpected end of file");
 177       return -1;
 178     }
 179     buf += r;
 180     count -= r;
 181     offset += r;
 182   }
 183
 184   return 0;
 185 }
 186
 187 /* Write data to the file. */
 188 static int
 189 example3_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
 190                  uint32_t flags)
 191 {
 192   struct example3_handle *h = handle;
 193
 194   while (count > 0) {
 195     ssize_t r = pwrite (h->fd, buf, count, offset);
 196     if (r == -1) {
 197       nbdkit_error ("pwrite: %m");
 198       return -1;
 199     }
 200     buf += r;
 201     count -= r;
 202     offset += r;
 203   }
 204
 205   return 0;
 206 }
 207
 208 /* Flush the file to disk. */
 209 static int
 210 example3_flush (void *handle, uint32_t flags)
 211 {
 212   struct example3_handle *h = handle;
 213
 214   if (fdatasync (h->fd) == -1) {
 215     nbdkit_error ("fdatasync: %m");
 216     return -1;
 217   }
 218
 219   return 0;
 220 }
 221
 222 static struct nbdkit_plugin plugin = {
 223   .name              = "example3",
 224   .version           = PACKAGE_VERSION,
 225   .dump_plugin       = example3_dump_plugin,
 226   .config            = example3_config,
 227   .config_help       = example3_config_help,
 228   .open              = example3_open,
 229   .close             = example3_close,
 230   .get_size          = example3_get_size,
 231   .pread             = example3_pread,
 232   .pwrite            = example3_pwrite,
 233   .flush             = example3_flush,
 234   /* In this plugin, errno is preserved properly along error return
 235    * paths from failed system calls.
 236    */
 237   .errno_is_preserved = 1,
 238 };
 239
 240 NBDKIT_REGISTER_PLUGIN (plugin)