plugins/full/full.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 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdint.h>
  38 #include <string.h>
  39 #include <errno.h>
  40
  41 #define NBDKIT_API_VERSION 2
  42
  43 #include <nbdkit-plugin.h>
  44
  45 /* The size of disk in bytes (initialized by size=<SIZE> parameter). */
  46 static int64_t size = -1;
  47
  48 static int
  49 full_config (const char *key, const char *value)
  50 {
  51   int64_t r;
  52
  53   if (strcmp (key, "size") == 0) {
  54     r = nbdkit_parse_size (value);
  55     if (r == -1)
  56       return -1;
  57     size = r;
  58   }
  59   else {
  60     nbdkit_error ("unknown parameter '%s'", key);
  61     return -1;
  62   }
  63
  64   return 0;
  65 }
  66
  67 static int
  68 full_config_complete (void)
  69 {
  70   if (size == -1) {
  71     nbdkit_error ("size parameter is required");
  72     return -1;
  73   }
  74
  75   return 0;
  76 }
  77
  78 #define full_config_help \
  79   "size=<SIZE>  (required) Size of the backing disk"
  80
  81 /* Create the per-connection handle. */
  82 static void *
  83 full_open (int readonly)
  84 {
  85   return NBDKIT_HANDLE_NOT_NEEDED;
  86 }
  87
  88 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
  89
  90 /* Get the disk size. */
  91 static int64_t
  92 full_get_size (void *handle)
  93 {
  94   return size;
  95 }
  96
  97 /* Serves the same data over multiple connections. */
  98 static int
  99 full_can_multi_conn (void *handle)
 100 {
 101   return 1;
 102 }
 103
 104 /* Cache. */
 105 static int
 106 full_can_cache (void *handle)
 107 {
 108   /* Everything is already in memory, returning this without
 109    * implementing .cache lets nbdkit do the correct no-op.
 110    */
 111   return NBDKIT_CACHE_NATIVE;
 112 }
 113
 114 /* Read data. */
 115 static int
 116 full_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
 117             uint32_t flags)
 118 {
 119   memset (buf, 0, count);
 120   return 0;
 121 }
 122
 123 /* Write data. */
 124 static int
 125 full_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
 126              uint32_t flags)
 127 {
 128   errno = ENOSPC;
 129   return -1;
 130 }
 131
 132 /* Omitting full_zero is intentional: that way, nbdkit defaults to
 133  * permitting fast zeroes which respond with ENOTSUP, while normal
 134  * zeroes fall back to pwrite and respond with ENOSPC.
 135  */
 136
 137 /* Trim. */
 138 static int
 139 full_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
 140 {
 141   errno = ENOSPC;
 142   return -1;
 143 }
 144
 145 /* Extents. */
 146 static int
 147 full_extents (void *handle, uint32_t count, uint64_t offset, uint32_t flags,
 148               struct nbdkit_extents *extents)
 149 {
 150   return nbdkit_add_extent (extents, 0, size,
 151                             NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO);
 152 }
 153
 154 /* Note that we don't need to handle flush: If there has been previous
 155  * write then we have already returned an error.  If there have been
 156  * no previous writes then flush can be ignored.
 157  */
 158
 159 static struct nbdkit_plugin plugin = {
 160   .name              = "full",
 161   .version           = PACKAGE_VERSION,
 162   .config            = full_config,
 163   .config_complete   = full_config_complete,
 164   .config_help       = full_config_help,
 165   .magic_config_key  = "size",
 166   .open              = full_open,
 167   .get_size          = full_get_size,
 168   .can_multi_conn    = full_can_multi_conn,
 169   .can_cache         = full_can_cache,
 170   .pread             = full_pread,
 171   .pwrite            = full_pwrite,
 172   .trim              = full_trim,
 173   .extents           = full_extents,
 174   /* In this plugin, errno is preserved properly along error return
 175    * paths from failed system calls.
 176    */
 177   .errno_is_preserved = 1,
 178 };
 179
 180 NBDKIT_REGISTER_PLUGIN (plugin)