plugins/zero/zero.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 <string.h>
  39 #include <errno.h>
  40
  41 #define NBDKIT_API_VERSION 2
  42 #include <nbdkit-plugin.h>
  43
  44 /* Create the per-connection handle. */
  45 static void *
  46 zero_open (int readonly)
  47 {
  48   return NBDKIT_HANDLE_NOT_NEEDED;
  49 }
  50
  51 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
  52
  53 /* Get the disk size. */
  54 static int64_t
  55 zero_get_size (void *handle)
  56 {
  57   return 0;
  58 }
  59
  60 /* Serves the same data over multiple connections. */
  61 static int
  62 zero_can_multi_conn (void *handle)
  63 {
  64   return 1;
  65 }
  66
  67 /* Cache. */
  68 static int
  69 zero_can_cache (void *handle)
  70 {
  71   /* Everything is already in memory, returning this without
  72    * implementing .cache lets nbdkit do the correct no-op.
  73    */
  74   return NBDKIT_CACHE_NATIVE;
  75 }
  76
  77 /* Ideally the read plugin would be optional. */
  78 static int
  79 zero_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
  80             uint32_t flags)
  81 {
  82   nbdkit_error ("unexpected call to pread");
  83   return -1;
  84 }
  85
  86 static struct nbdkit_plugin plugin = {
  87   .name              = "zero",
  88   .version           = PACKAGE_VERSION,
  89   .open              = zero_open,
  90   .get_size          = zero_get_size,
  91   .can_multi_conn    = zero_can_multi_conn,
  92   .can_cache         = zero_can_cache,
  93   .pread             = zero_pread,
  94   /* In this plugin, errno is preserved properly along error return
  95    * paths from failed system calls.
  96    */
  97   .errno_is_preserved = 1,
  98 };
  99
 100 NBDKIT_REGISTER_PLUGIN(plugin)