plugins/random/random.c

   1 /* nbdkit
   2  * Copyright (C) 2017-2019 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 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdint.h>
  38 #include <inttypes.h>
  39 #include <string.h>
  40 #include <errno.h>
  41 #include <time.h>
  42
  43 #define NBDKIT_API_VERSION 2
  44 #include <nbdkit-plugin.h>
  45
  46 #include "random.h"
  47
  48 /* The size of disk in bytes (initialized by size=<SIZE> parameter). */
  49 static int64_t size = 0;
  50
  51 /* Seed. */
  52 static uint32_t seed;
  53
  54 static void
  55 random_load (void)
  56 {
  57   /* Set the seed to a random-ish value.  This is not meant to be
  58    * cryptographically useful.  It can be overridden using the seed
  59    * parameter.
  60    */
  61   seed = time (NULL);
  62 }
  63
  64 static int
  65 random_config (const char *key, const char *value)
  66 {
  67   int64_t r;
  68
  69   if (strcmp (key, "seed") == 0) {
  70     if (nbdkit_parse_uint32_t ("seed", value, &seed) == -1)
  71       return -1;
  72   }
  73   else if (strcmp (key, "size") == 0) {
  74     r = nbdkit_parse_size (value);
  75     if (r == -1)
  76       return -1;
  77     size = r;
  78   }
  79   else {
  80     nbdkit_error ("unknown parameter '%s'", key);
  81     return -1;
  82   }
  83
  84   return 0;
  85 }
  86
  87 #define random_config_help \
  88   "size=<SIZE>  (required) Size of the backing disk\n" \
  89   "seed=<SEED>             Random number generator seed"
  90
  91 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
  92
  93 /* Create the per-connection handle. */
  94 static void *
  95 random_open (int readonly)
  96 {
  97   return NBDKIT_HANDLE_NOT_NEEDED;
  98 }
  99
 100 /* Get the disk size. */
 101 static int64_t
 102 random_get_size (void *handle)
 103 {
 104   return size;
 105 }
 106
 107 /* Serves the same data over multiple connections. */
 108 static int
 109 random_can_multi_conn (void *handle)
 110 {
 111   return 1;
 112 }
 113
 114 /* Cache. */
 115 static int
 116 random_can_cache (void *handle)
 117 {
 118   /* Everything is already in memory, returning this without
 119    * implementing .cache lets nbdkit do the correct no-op.
 120    */
 121   return NBDKIT_CACHE_NATIVE;
 122 }
 123
 124 /* Read data. */
 125 static int
 126 random_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
 127               uint32_t flags)
 128 {
 129   uint32_t i;
 130   unsigned char *b = buf;
 131   uint64_t s;
 132
 133   for (i = 0; i < count; ++i) {
 134     /* We use nbdkit common/include/random.h to make random numbers.
 135      *
 136      * However we're not quite using it in the ordinary way.  In order
 137      * to be able to read any byte of data without needing to run the
 138      * PRNG from the start, the random data is computed from the index
 139      * and seed through three rounds of PRNG:
 140      *
 141      * index i     PRNG(seed+i)   -> PRNG -> PRNG -> mod 256 -> b[i]
 142      * index i+1   PRNG(seed+i+1) -> PRNG -> PRNG -> mod 256 -> b[i+1]
 143      * etc
 144      */
 145     struct random_state state;
 146
 147     xsrandom (seed + offset + i, &state);
 148     xrandom (&state);
 149     xrandom (&state);
 150     s = xrandom (&state);
 151     s &= 255;
 152     b[i] = s;
 153   }
 154   return 0;
 155 }
 156
 157 static struct nbdkit_plugin plugin = {
 158   .name              = "random",
 159   .version           = PACKAGE_VERSION,
 160   .load              = random_load,
 161   .config            = random_config,
 162   .config_help       = random_config_help,
 163   .magic_config_key  = "size",
 164   .open              = random_open,
 165   .get_size          = random_get_size,
 166   .can_multi_conn    = random_can_multi_conn,
 167   .can_cache         = random_can_cache,
 168   .pread             = random_pread,
 169   /* In this plugin, errno is preserved properly along error return
 170    * paths from failed system calls.
 171    */
 172   .errno_is_preserved = 1,
 173 };
 174
 175 NBDKIT_REGISTER_PLUGIN(plugin)