filters/nocache/nocache.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 <stdbool.h>
  40 #include <assert.h>
  41
  42 #include <nbdkit-filter.h>
  43
  44 #include "minmax.h"
  45
  46 static enum CacheMode {
  47   NONE,
  48   EMULATE,
  49   NOP,
  50 } cachemode;
  51
  52 static int
  53 nocache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
  54                 const char *key, const char *value)
  55 {
  56   if (strcmp (key, "cachemode") == 0) {
  57     if (strcmp (value, "emulate") == 0)
  58       cachemode = EMULATE;
  59     else if (strcmp (value, "nop") == 0 ||
  60              strcmp (value, "no-op") == 0)
  61       cachemode = NOP;
  62     else if (strcmp (value, "none") != 0) {
  63       nbdkit_error ("unknown cachemode '%s'", value);
  64       return -1;
  65     }
  66     return 0;
  67   }
  68   return next (nxdata, key, value);
  69 }
  70
  71 #define nocache_config_help \
  72   "cachemode=<MODE>     Either 'none' (default), 'emulate', or 'nop'.\n" \
  73
  74 /* Advertise desired FLAG_SEND_CACHE mode. */
  75 static int
  76 nocache_can_cache (nbdkit_next *next,
  77                    void *handle)
  78 {
  79   switch (cachemode) {
  80   case NONE:
  81     return NBDKIT_CACHE_NONE;
  82   case EMULATE:
  83     return NBDKIT_CACHE_EMULATE;
  84   case NOP:
  85     return NBDKIT_CACHE_NATIVE;
  86   }
  87   abort ();
  88 }
  89
  90 static int
  91 nocache_cache (nbdkit_next *next,
  92                void *handle, uint32_t count, uint64_t offs, uint32_t flags,
  93                int *err)
  94 {
  95   assert (cachemode == NOP);
  96   assert (!flags);
  97
  98   return 0;
  99 }
 100
 101 static struct nbdkit_filter filter = {
 102   .name              = "nocache",
 103   .longname          = "nbdkit nocache filter",
 104   .config            = nocache_config,
 105   .config_help       = nocache_config_help,
 106   .can_cache         = nocache_can_cache,
 107   .cache             = nocache_cache,
 108 };
 109
 110 NBDKIT_REGISTER_FILTER (filter)