plugins/null/null.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 = 0;
  47
  48 static int
  49 null_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 #define null_config_help \
  68   "size=<SIZE>             Size of the backing disk"
  69
  70 /* Create the per-connection handle. */
  71 static void *
  72 null_open (int readonly)
  73 {
  74   return NBDKIT_HANDLE_NOT_NEEDED;
  75 }
  76
  77 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
  78
  79 /* Get the disk size. */
  80 static int64_t
  81 null_get_size (void *handle)
  82 {
  83   return size;
  84 }
  85
  86 /* Serves the same data over multiple connections. */
  87 static int
  88 null_can_multi_conn (void *handle)
  89 {
  90   return 1;
  91 }
  92
  93 /* Cache. */
  94 static int
  95 null_can_cache (void *handle)
  96 {
  97   /* Everything is already in memory, returning this without
  98    * implementing .cache lets nbdkit do the correct no-op.
  99    */
 100   return NBDKIT_CACHE_NATIVE;
 101 }
 102
 103 /* Fast zero. */
 104 static int
 105 null_can_fast_zero (void *handle)
 106 {
 107   return 1;
 108 }
 109
 110 /* Read data. */
 111 static int
 112 null_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
 113             uint32_t flags)
 114 {
 115   memset (buf, 0, count);
 116   return 0;
 117 }
 118
 119 /* Write data. */
 120 static int
 121 null_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
 122              uint32_t flags)
 123 {
 124   /* nothing */
 125   return 0;
 126 }
 127
 128 /* Write zeroes. */
 129 static int
 130 null_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
 131 {
 132   /* nothing */
 133   return 0;
 134 }
 135
 136 /* Flush is a no-op, so advertise native FUA support */
 137 static int
 138 null_can_fua (void *handle)
 139 {
 140   return NBDKIT_FUA_NATIVE;
 141 }
 142
 143 /* Trim. */
 144 static int
 145 null_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
 146 {
 147   /* nothing */
 148   return 0;
 149 }
 150
 151 /* Nothing is persistent, so flush is trivially supported */
 152 static int
 153 null_flush (void *handle, uint32_t flags)
 154 {
 155   return 0;
 156 }
 157
 158 /* Extents. */
 159 static int
 160 null_extents (void *handle, uint32_t count, uint64_t offset, uint32_t flags,
 161               struct nbdkit_extents *extents)
 162 {
 163   return nbdkit_add_extent (extents, 0, size,
 164                             NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO);
 165 }
 166
 167 static struct nbdkit_plugin plugin = {
 168   .name              = "null",
 169   .version           = PACKAGE_VERSION,
 170   .config            = null_config,
 171   .config_help       = null_config_help,
 172   .magic_config_key  = "size",
 173   .open              = null_open,
 174   .get_size          = null_get_size,
 175   .can_multi_conn    = null_can_multi_conn,
 176   .can_cache         = null_can_cache,
 177   .can_fast_zero     = null_can_fast_zero,
 178   .pread             = null_pread,
 179   .pwrite            = null_pwrite,
 180   .zero              = null_zero,
 181   .trim              = null_trim,
 182   .can_fua           = null_can_fua,
 183   .flush             = null_flush,
 184   .extents           = null_extents,
 185   /* In this plugin, errno is preserved properly along error return
 186    * paths from failed system calls.
 187    */
 188   .errno_is_preserved = 1,
 189 };
 190
 191 NBDKIT_REGISTER_PLUGIN (plugin)